// SPDX-License-Identifier: GPL-2.0
#include <linux/ceph/ceph_debug.h>

#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/writeback.h>
#include <linux/iversion.h>

#include "super.h"
#include "mds_client.h"
#include "cache.h"
#include <linux/ceph/decode.h>
#include <linux/ceph/messenger.h>

/*
 * Capability management
 *
 * The Ceph metadata servers control client access to inode metadata
 * and file data by issuing capabilities, granting clients permission
 * to read and/or write both inode field and file data to OSDs
 * (storage nodes).  Each capability consists of a set of bits
 * indicating which operations are allowed.
 *
 * If the client holds a *_SHARED cap, the client has a coherent value
 * that can be safely read from the cached inode.
 *
 * In the case of a *_EXCL (exclusive) or FILE_WR capabilities, the
 * client is allowed to change inode attributes (e.g., file size,
 * mtime), note its dirty state in the ceph_cap, and asynchronously
 * flush that metadata change to the MDS.
 *
 * In the event of a conflicting operation (perhaps by another
 * client), the MDS will revoke the conflicting client capabilities.
 *
 * In order for a client to cache an inode, it must hold a capability
 * with at least one MDS server.  When inodes are released, release
 * notifications are batched and periodically sent en masse to the MDS
 * cluster to release server state.
 */

static u64 __get_oldest_flush_tid(struct ceph_mds_client *mdsc);
static void __kick_flushing_caps(struct ceph_mds_client *mdsc,
                                 struct ceph_mds_session *session,
                                 struct ceph_inode_info *ci,
                                 u64 oldest_flush_tid);

/*
 * Generate readable cap strings for debugging output.
 */
#define MAX_CAP_STR 20
static char cap_str[MAX_CAP_STR][40];
static DEFINE_SPINLOCK(cap_str_lock);
static int last_cap_str;

static char *gcap_string(char *s, int c)
{
        if (c & CEPH_CAP_GSHARED)
                *s++ = 's';
        if (c & CEPH_CAP_GEXCL)
                *s++ = 'x';
        if (c & CEPH_CAP_GCACHE)
                *s++ = 'c';
        if (c & CEPH_CAP_GRD)
                *s++ = 'r';
        if (c & CEPH_CAP_GWR)
                *s++ = 'w';
        if (c & CEPH_CAP_GBUFFER)
                *s++ = 'b';
        if (c & CEPH_CAP_GWREXTEND)
                *s++ = 'a';
        if (c & CEPH_CAP_GLAZYIO)
                *s++ = 'l';
        return s;
}

const char *ceph_cap_string(int caps)
{
        int i;
        char *s;
        int c;

        spin_lock(&cap_str_lock);
        i = last_cap_str++;
        if (last_cap_str == MAX_CAP_STR)
                last_cap_str = 0;
        spin_unlock(&cap_str_lock);

        s = cap_str[i];

        if (caps & CEPH_CAP_PIN)
                *s++ = 'p';

        c = (caps >> CEPH_CAP_SAUTH) & 3;
        if (c) {
                *s++ = 'A';
                s = gcap_string(s, c);
        }

        c = (caps >> CEPH_CAP_SLINK) & 3;
        if (c) {
                *s++ = 'L';
                s = gcap_string(s, c);
        }

        c = (caps >> CEPH_CAP_SXATTR) & 3;
        if (c) {
                *s++ = 'X';
                s = gcap_string(s, c);
        }

        c = caps >> CEPH_CAP_SFILE;
        if (c) {
                *s++ = 'F';
                s = gcap_string(s, c);
        }

        if (s == cap_str[i])
                *s++ = '-';
        *s = 0;
        return cap_str[i];
}

void ceph_caps_init(struct ceph_mds_client *mdsc)
{
        INIT_LIST_HEAD(&mdsc->caps_list);
        spin_lock_init(&mdsc->caps_list_lock);
}

void ceph_caps_finalize(struct ceph_mds_client *mdsc)
{
        struct ceph_cap *cap;

        spin_lock(&mdsc->caps_list_lock);
        while (!list_empty(&mdsc->caps_list)) {
                cap = list_first_entry(&mdsc->caps_list,
                                       struct ceph_cap, caps_item);
                list_del(&cap->caps_item);
                kmem_cache_free(ceph_cap_cachep, cap);
        }
        mdsc->caps_total_count = 0;
        mdsc->caps_avail_count = 0;
        mdsc->caps_use_count = 0;
        mdsc->caps_reserve_count = 0;
        mdsc->caps_min_count = 0;
        spin_unlock(&mdsc->caps_list_lock);
}

void ceph_adjust_caps_max_min(struct ceph_mds_client *mdsc,
                              struct ceph_mount_options *fsopt)
{
        spin_lock(&mdsc->caps_list_lock);
        mdsc->caps_min_count = fsopt->max_readdir;
        if (mdsc->caps_min_count < 1024)
                mdsc->caps_min_count = 1024;
        mdsc->caps_use_max = fsopt->caps_max;
        if (mdsc->caps_use_max > 0 &&
            mdsc->caps_use_max < mdsc->caps_min_count)
                mdsc->caps_use_max = mdsc->caps_min_count;
        spin_unlock(&mdsc->caps_list_lock);
}

static void __ceph_unreserve_caps(struct ceph_mds_client *mdsc, int nr_caps)
{
        struct ceph_cap *cap;
        int i;

        if (nr_caps) {
                BUG_ON(mdsc->caps_reserve_count < nr_caps);
                mdsc->caps_reserve_count -= nr_caps;
                if (mdsc->caps_avail_count >=
                    mdsc->caps_reserve_count + mdsc->caps_min_count) {
                        mdsc->caps_total_count -= nr_caps;
                        for (i = 0; i < nr_caps; i++) {
                                cap = list_first_entry(&mdsc->caps_list,
                                        struct ceph_cap, caps_item);
                                list_del(&cap->caps_item);
                                kmem_cache_free(ceph_cap_cachep, cap);
                        }
                } else {
                        mdsc->caps_avail_count += nr_caps;
                }

                dout("%s: caps %d = %d used + %d resv + %d avail\n",
                     __func__,
                     mdsc->caps_total_count, mdsc->caps_use_count,
                     mdsc->caps_reserve_count, mdsc->caps_avail_count);
                BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
                                                 mdsc->caps_reserve_count +
                                                 mdsc->caps_avail_count);
        }
}

/*
 * Called under mdsc->mutex.
 */
int ceph_reserve_caps(struct ceph_mds_client *mdsc,
                      struct ceph_cap_reservation *ctx, int need)
{
        int i, j;
        struct ceph_cap *cap;
        int have;
        int alloc = 0;
        int max_caps;
        int err = 0;
        bool trimmed = false;
        struct ceph_mds_session *s;
        LIST_HEAD(newcaps);

        dout("reserve caps ctx=%p need=%d\n", ctx, need);

        /* first reserve any caps that are already allocated */
        spin_lock(&mdsc->caps_list_lock);
        if (mdsc->caps_avail_count >= need)
                have = need;
        else
                have = mdsc->caps_avail_count;
        mdsc->caps_avail_count -= have;
        mdsc->caps_reserve_count += have;
        BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
                                         mdsc->caps_reserve_count +
                                         mdsc->caps_avail_count);
        spin_unlock(&mdsc->caps_list_lock);

        for (i = have; i < need; ) {
                cap = kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);
                if (cap) {
                        list_add(&cap->caps_item, &newcaps);
                        alloc++;
                        i++;
                        continue;
                }

                if (!trimmed) {
                        for (j = 0; j < mdsc->max_sessions; j++) {
                                s = __ceph_lookup_mds_session(mdsc, j);
                                if (!s)
                                        continue;
                                mutex_unlock(&mdsc->mutex);

                                mutex_lock(&s->s_mutex);
                                max_caps = s->s_nr_caps - (need - i);
                                ceph_trim_caps(mdsc, s, max_caps);
                                mutex_unlock(&s->s_mutex);

                                ceph_put_mds_session(s);
                                mutex_lock(&mdsc->mutex);
                        }
                        trimmed = true;

                        spin_lock(&mdsc->caps_list_lock);
                        if (mdsc->caps_avail_count) {
                                int more_have;
                                if (mdsc->caps_avail_count >= need - i)
                                        more_have = need - i;
                                else
                                        more_have = mdsc->caps_avail_count;

                                i += more_have;
                                have += more_have;
                                mdsc->caps_avail_count -= more_have;
                                mdsc->caps_reserve_count += more_have;

                        }
                        spin_unlock(&mdsc->caps_list_lock);

                        continue;
                }

                pr_warn("reserve caps ctx=%p ENOMEM need=%d got=%d\n",
                        ctx, need, have + alloc);
                err = -ENOMEM;
                break;
        }

        if (!err) {
                BUG_ON(have + alloc != need);
                ctx->count = need;
                ctx->used = 0;
        }

        spin_lock(&mdsc->caps_list_lock);
        mdsc->caps_total_count += alloc;
        mdsc->caps_reserve_count += alloc;
        list_splice(&newcaps, &mdsc->caps_list);

        BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
                                         mdsc->caps_reserve_count +
                                         mdsc->caps_avail_count);

        if (err)
                __ceph_unreserve_caps(mdsc, have + alloc);

        spin_unlock(&mdsc->caps_list_lock);

        dout("reserve caps ctx=%p %d = %d used + %d resv + %d avail\n",
             ctx, mdsc->caps_total_count, mdsc->caps_use_count,
             mdsc->caps_reserve_count, mdsc->caps_avail_count);
        return err;
}

void ceph_unreserve_caps(struct ceph_mds_client *mdsc,
                         struct ceph_cap_reservation *ctx)
{
        bool reclaim = false;
        if (!ctx->count)
                return;

        dout("unreserve caps ctx=%p count=%d\n", ctx, ctx->count);
        spin_lock(&mdsc->caps_list_lock);
        __ceph_unreserve_caps(mdsc, ctx->count);
        ctx->count = 0;

        if (mdsc->caps_use_max > 0 &&
            mdsc->caps_use_count > mdsc->caps_use_max)
                reclaim = true;
        spin_unlock(&mdsc->caps_list_lock);

        if (reclaim)
                ceph_reclaim_caps_nr(mdsc, ctx->used);
}

struct ceph_cap *ceph_get_cap(struct ceph_mds_client *mdsc,
                              struct ceph_cap_reservation *ctx)
{
        struct ceph_cap *cap = NULL;

        /* temporary, until we do something about cap import/export */
        if (!ctx) {
                cap = kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);
                if (cap) {
                        spin_lock(&mdsc->caps_list_lock);
                        mdsc->caps_use_count++;
                        mdsc->caps_total_count++;
                        spin_unlock(&mdsc->caps_list_lock);
                } else {
                        spin_lock(&mdsc->caps_list_lock);
                        if (mdsc->caps_avail_count) {
                                BUG_ON(list_empty(&mdsc->caps_list));

                                mdsc->caps_avail_count--;
                                mdsc->caps_use_count++;
                                cap = list_first_entry(&mdsc->caps_list,
                                                struct ceph_cap, caps_item);
                                list_del(&cap->caps_item);

                                BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
                                       mdsc->caps_reserve_count + mdsc->caps_avail_count);
                        }
                        spin_unlock(&mdsc->caps_list_lock);
                }

                return cap;
        }

        spin_lock(&mdsc->caps_list_lock);
        dout("get_cap ctx=%p (%d) %d = %d used + %d resv + %d avail\n",
             ctx, ctx->count, mdsc->caps_total_count, mdsc->caps_use_count,
             mdsc->caps_reserve_count, mdsc->caps_avail_count);
        BUG_ON(!ctx->count);
        BUG_ON(ctx->count > mdsc->caps_reserve_count);
        BUG_ON(list_empty(&mdsc->caps_list));

        ctx->count--;
        ctx->used++;
        mdsc->caps_reserve_count--;
        mdsc->caps_use_count++;

        cap = list_first_entry(&mdsc->caps_list, struct ceph_cap, caps_item);
        list_del(&cap->caps_item);

        BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
               mdsc->caps_reserve_count + mdsc->caps_avail_count);
        spin_unlock(&mdsc->caps_list_lock);
        return cap;
}

void ceph_put_cap(struct ceph_mds_client *mdsc, struct ceph_cap *cap)
{
        spin_lock(&mdsc->caps_list_lock);
        dout("put_cap %p %d = %d used + %d resv + %d avail\n",
             cap, mdsc->caps_total_count, mdsc->caps_use_count,
             mdsc->caps_reserve_count, mdsc->caps_avail_count);
        mdsc->caps_use_count--;
        /*
         * Keep some preallocated caps around (ceph_min_count), to
         * avoid lots of free/alloc churn.
         */
        if (mdsc->caps_avail_count >= mdsc->caps_reserve_count +
                                      mdsc->caps_min_count) {
                mdsc->caps_total_count--;
                kmem_cache_free(ceph_cap_cachep, cap);
        } else {
                mdsc->caps_avail_count++;
                list_add(&cap->caps_item, &mdsc->caps_list);
        }

        BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
               mdsc->caps_reserve_count + mdsc->caps_avail_count);
        spin_unlock(&mdsc->caps_list_lock);
}

void ceph_reservation_status(struct ceph_fs_client *fsc,
                             int *total, int *avail, int *used, int *reserved,
                             int *min)
{
        struct ceph_mds_client *mdsc = fsc->mdsc;

        spin_lock(&mdsc->caps_list_lock);

        if (total)
                *total = mdsc->caps_total_count;
        if (avail)
                *avail = mdsc->caps_avail_count;
        if (used)
                *used = mdsc->caps_use_count;
        if (reserved)
                *reserved = mdsc->caps_reserve_count;
        if (min)
                *min = mdsc->caps_min_count;

        spin_unlock(&mdsc->caps_list_lock);
}

/*
 * Find ceph_cap for given mds, if any.
 *
 * Called with i_ceph_lock held.
 */
static struct ceph_cap *__get_cap_for_mds(struct ceph_inode_info *ci, int mds)
{
        struct ceph_cap *cap;
        struct rb_node *n = ci->i_caps.rb_node;

        while (n) {
                cap = rb_entry(n, struct ceph_cap, ci_node);
                if (mds < cap->mds)
                        n = n->rb_left;
                else if (mds > cap->mds)
                        n = n->rb_right;
                else
                        return cap;
        }
        return NULL;
}

struct ceph_cap *ceph_get_cap_for_mds(struct ceph_inode_info *ci, int mds)
{
        struct ceph_cap *cap;

        spin_lock(&ci->i_ceph_lock);
        cap = __get_cap_for_mds(ci, mds);
        spin_unlock(&ci->i_ceph_lock);
        return cap;
}

/*
 * Called under i_ceph_lock.
 */
static void __insert_cap_node(struct ceph_inode_info *ci,
                              struct ceph_cap *new)
{
        struct rb_node **p = &ci->i_caps.rb_node;
        struct rb_node *parent = NULL;
        struct ceph_cap *cap = NULL;

        while (*p) {
                parent = *p;
                cap = rb_entry(parent, struct ceph_cap, ci_node);
                if (new->mds < cap->mds)
                        p = &(*p)->rb_left;
                else if (new->mds > cap->mds)
                        p = &(*p)->rb_right;
                else
                        BUG();
        }

        rb_link_node(&new->ci_node, parent, p);
        rb_insert_color(&new->ci_node, &ci->i_caps);
}

/*
 * (re)set cap hold timeouts, which control the delayed release
 * of unused caps back to the MDS.  Should be called on cap use.
 */
static void __cap_set_timeouts(struct ceph_mds_client *mdsc,
                               struct ceph_inode_info *ci)
{
        struct ceph_mount_options *opt = mdsc->fsc->mount_options;
        ci->i_hold_caps_max = round_jiffies(jiffies +
                                            opt->caps_wanted_delay_max * HZ);
        dout("__cap_set_timeouts %p %lu\n", &ci->vfs_inode,
             ci->i_hold_caps_max - jiffies);
}

/*
 * (Re)queue cap at the end of the delayed cap release list.
 *
 * If I_FLUSH is set, leave the inode at the front of the list.
 *
 * Caller holds i_ceph_lock
 *    -> we take mdsc->cap_delay_lock
 */
static void __cap_delay_requeue(struct ceph_mds_client *mdsc,
                                struct ceph_inode_info *ci)
{
        dout("__cap_delay_requeue %p flags 0x%lx at %lu\n", &ci->vfs_inode,
             ci->i_ceph_flags, ci->i_hold_caps_max);
        if (!mdsc->stopping) {
                spin_lock(&mdsc->cap_delay_lock);
                if (!list_empty(&ci->i_cap_delay_list)) {
                        if (ci->i_ceph_flags & CEPH_I_FLUSH)
                                goto no_change;
                        list_del_init(&ci->i_cap_delay_list);
                }
                __cap_set_timeouts(mdsc, ci);
                list_add_tail(&ci->i_cap_delay_list, &mdsc->cap_delay_list);
no_change:
                spin_unlock(&mdsc->cap_delay_lock);
        }
}

/*
 * Queue an inode for immediate writeback.  Mark inode with I_FLUSH,
 * indicating we should send a cap message to flush dirty metadata
 * asap, and move to the front of the delayed cap list.
 */
static void __cap_delay_requeue_front(struct ceph_mds_client *mdsc,
                                      struct ceph_inode_info *ci)
{
        dout("__cap_delay_requeue_front %p\n", &ci->vfs_inode);
        spin_lock(&mdsc->cap_delay_lock);
        ci->i_ceph_flags |= CEPH_I_FLUSH;
        if (!list_empty(&ci->i_cap_delay_list))
                list_del_init(&ci->i_cap_delay_list);
        list_add(&ci->i_cap_delay_list, &mdsc->cap_delay_list);
        spin_unlock(&mdsc->cap_delay_lock);
}

/*
 * Cancel delayed work on cap.
 *
 * Caller must hold i_ceph_lock.
 */
static void __cap_delay_cancel(struct ceph_mds_client *mdsc,
                               struct ceph_inode_info *ci)
{
        dout("__cap_delay_cancel %p\n", &ci->vfs_inode);
        if (list_empty(&ci->i_cap_delay_list))
                return;
        spin_lock(&mdsc->cap_delay_lock);
        list_del_init(&ci->i_cap_delay_list);
        spin_unlock(&mdsc->cap_delay_lock);
}

/* Common issue checks for add_cap, handle_cap_grant. */
static void __check_cap_issue(struct ceph_inode_info *ci, struct ceph_cap *cap,
                              unsigned issued)
{
        unsigned had = __ceph_caps_issued(ci, NULL);

        lockdep_assert_held(&ci->i_ceph_lock);

        /*
         * Each time we receive FILE_CACHE anew, we increment
         * i_rdcache_gen.
         */
        if (S_ISREG(ci->vfs_inode.i_mode) &&
            (issued & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) &&
            (had & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) == 0) {
                ci->i_rdcache_gen++;
        }

        /*
         * If FILE_SHARED is newly issued, mark dir not complete. We don't
         * know what happened to this directory while we didn't have the cap.
         * If FILE_SHARED is being revoked, also mark dir not complete. It
         * stops on-going cached readdir.
         */
        if ((issued & CEPH_CAP_FILE_SHARED) != (had & CEPH_CAP_FILE_SHARED)) {
                if (issued & CEPH_CAP_FILE_SHARED)
                        atomic_inc(&ci->i_shared_gen);
                if (S_ISDIR(ci->vfs_inode.i_mode)) {
                        dout(" marking %p NOT complete\n", &ci->vfs_inode);
                        __ceph_dir_clear_complete(ci);
                }
        }

        /* Wipe saved layout if we're losing DIR_CREATE caps */
        if (S_ISDIR(ci->vfs_inode.i_mode) && (had & CEPH_CAP_DIR_CREATE) &&
                !(issued & CEPH_CAP_DIR_CREATE)) {
             ceph_put_string(rcu_dereference_raw(ci->i_cached_layout.pool_ns));
             memset(&ci->i_cached_layout, 0, sizeof(ci->i_cached_layout));
        }
}

/**
 * change_auth_cap_ses - move inode to appropriate lists when auth caps change
 * @ci: inode to be moved
 * @session: new auth caps session
 */
static void change_auth_cap_ses(struct ceph_inode_info *ci,
                                struct ceph_mds_session *session)
{
        lockdep_assert_held(&ci->i_ceph_lock);

        if (list_empty(&ci->i_dirty_item) && list_empty(&ci->i_flushing_item))
                return;

        spin_lock(&session->s_mdsc->cap_dirty_lock);
        if (!list_empty(&ci->i_dirty_item))
                list_move(&ci->i_dirty_item, &session->s_cap_dirty);
        if (!list_empty(&ci->i_flushing_item))
                list_move_tail(&ci->i_flushing_item, &session->s_cap_flushing);
        spin_unlock(&session->s_mdsc->cap_dirty_lock);
}

/*
 * Add a capability under the given MDS session.
 *
 * Caller should hold session snap_rwsem (read) and ci->i_ceph_lock
 *
 * @fmode is the open file mode, if we are opening a file, otherwise
 * it is < 0.  (This is so we can atomically add the cap and add an
 * open file reference to it.)
 */
void ceph_add_cap(struct inode *inode,
                  struct ceph_mds_session *session, u64 cap_id,
                  unsigned issued, unsigned wanted,
                  unsigned seq, unsigned mseq, u64 realmino, int flags,
                  struct ceph_cap **new_cap)
{
        struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_cap *cap;
        int mds = session->s_mds;
        int actual_wanted;
        u32 gen;

        lockdep_assert_held(&ci->i_ceph_lock);

        dout("add_cap %p mds%d cap %llx %s seq %d\n", inode,
             session->s_mds, cap_id, ceph_cap_string(issued), seq);

        gen = atomic_read(&session->s_cap_gen);

        cap = __get_cap_for_mds(ci, mds);
        if (!cap) {
                cap = *new_cap;
                *new_cap = NULL;

                cap->issued = 0;
                cap->implemented = 0;
                cap->mds = mds;
                cap->mds_wanted = 0;
                cap->mseq = 0;

                cap->ci = ci;
                __insert_cap_node(ci, cap);

                /* add to session cap list */
                cap->session = session;
                spin_lock(&session->s_cap_lock);
                list_add_tail(&cap->session_caps, &session->s_caps);
                session->s_nr_caps++;
                atomic64_inc(&mdsc->metric.total_caps);
                spin_unlock(&session->s_cap_lock);
        } else {
                spin_lock(&session->s_cap_lock);
                list_move_tail(&cap->session_caps, &session->s_caps);
                spin_unlock(&session->s_cap_lock);

                if (cap->cap_gen < gen)
                        cap->issued = cap->implemented = CEPH_CAP_PIN;

                /*
                 * auth mds of the inode changed. we received the cap export
                 * message, but still haven't received the cap import message.
                 * handle_cap_export() updated the new auth MDS' cap.
                 *
                 * "ceph_seq_cmp(seq, cap->seq) <= 0" means we are processing
                 * a message that was send before the cap import message. So
                 * don't remove caps.
                 */
                if (ceph_seq_cmp(seq, cap->seq) <= 0) {
                        WARN_ON(cap != ci->i_auth_cap);
                        WARN_ON(cap->cap_id != cap_id);
                        seq = cap->seq;
                        mseq = cap->mseq;
                        issued |= cap->issued;
                        flags |= CEPH_CAP_FLAG_AUTH;
                }
        }

        if (!ci->i_snap_realm ||
            ((flags & CEPH_CAP_FLAG_AUTH) &&
             realmino != (u64)-1 && ci->i_snap_realm->ino != realmino)) {
                /*
                 * add this inode to the appropriate snap realm
                 */
                struct ceph_snap_realm *realm = ceph_lookup_snap_realm(mdsc,
                                                               realmino);
                if (realm) {
                        struct ceph_snap_realm *oldrealm = ci->i_snap_realm;
                        if (oldrealm) {
                                spin_lock(&oldrealm->inodes_with_caps_lock);
                                list_del_init(&ci->i_snap_realm_item);
                                spin_unlock(&oldrealm->inodes_with_caps_lock);
                        }

                        spin_lock(&realm->inodes_with_caps_lock);
                        list_add(&ci->i_snap_realm_item,
                                 &realm->inodes_with_caps);
                        ci->i_snap_realm = realm;
                        if (realm->ino == ci->i_vino.ino)
                                realm->inode = inode;
                        spin_unlock(&realm->inodes_with_caps_lock);

                        if (oldrealm)
                                ceph_put_snap_realm(mdsc, oldrealm);
                } else {
                        pr_err("ceph_add_cap: couldn't find snap realm %llx\n",
                               realmino);
                        WARN_ON(!realm);
                }
        }

        __check_cap_issue(ci, cap, issued);

        /*
         * If we are issued caps we don't want, or the mds' wanted
         * value appears to be off, queue a check so we'll release
         * later and/or update the mds wanted value.
         */
        actual_wanted = __ceph_caps_wanted(ci);
        if ((wanted & ~actual_wanted) ||
            (issued & ~actual_wanted & CEPH_CAP_ANY_WR)) {
                dout(" issued %s, mds wanted %s, actual %s, queueing\n",
                     ceph_cap_string(issued), ceph_cap_string(wanted),
                     ceph_cap_string(actual_wanted));
                __cap_delay_requeue(mdsc, ci);
        }

        if (flags & CEPH_CAP_FLAG_AUTH) {
                if (!ci->i_auth_cap ||
                    ceph_seq_cmp(ci->i_auth_cap->mseq, mseq) < 0) {
                        if (ci->i_auth_cap &&
                            ci->i_auth_cap->session != cap->session)
                                change_auth_cap_ses(ci, cap->session);
                        ci->i_auth_cap = cap;
                        cap->mds_wanted = wanted;
                }
        } else {
                WARN_ON(ci->i_auth_cap == cap);
        }

        dout("add_cap inode %p (%llx.%llx) cap %p %s now %s seq %d mds%d\n",
             inode, ceph_vinop(inode), cap, ceph_cap_string(issued),
             ceph_cap_string(issued|cap->issued), seq, mds);
        cap->cap_id = cap_id;
        cap->issued = issued;
        cap->implemented |= issued;
        if (ceph_seq_cmp(mseq, cap->mseq) > 0)
                cap->mds_wanted = wanted;
        else
                cap->mds_wanted |= wanted;
        cap->seq = seq;
        cap->issue_seq = seq;
        cap->mseq = mseq;
        cap->cap_gen = gen;
}

/*
 * Return true if cap has not timed out and belongs to the current
 * generation of the MDS session (i.e. has not gone 'stale' due to
 * us losing touch with the mds).
 */
static int __cap_is_valid(struct ceph_cap *cap)
{
        unsigned long ttl;
        u32 gen;

        gen = atomic_read(&cap->session->s_cap_gen);
        ttl = cap->session->s_cap_ttl;

        if (cap->cap_gen < gen || time_after_eq(jiffies, ttl)) {
                dout("__cap_is_valid %p cap %p issued %s "
                     "but STALE (gen %u vs %u)\n", &cap->ci->vfs_inode,
                     cap, ceph_cap_string(cap->issued), cap->cap_gen, gen);
                return 0;
        }

        return 1;
}

/*
 * Return set of valid cap bits issued to us.  Note that caps time
 * out, and may be invalidated in bulk if the client session times out
 * and session->s_cap_gen is bumped.
 */
int __ceph_caps_issued(struct ceph_inode_info *ci, int *implemented)
{
        int have = ci->i_snap_caps;
        struct ceph_cap *cap;
        struct rb_node *p;

        if (implemented)
                *implemented = 0;
        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (!__cap_is_valid(cap))
                        continue;
                dout("__ceph_caps_issued %p cap %p issued %s\n",
                     &ci->vfs_inode, cap, ceph_cap_string(cap->issued));
                have |= cap->issued;
                if (implemented)
                        *implemented |= cap->implemented;
        }
        /*
         * exclude caps issued by non-auth MDS, but are been revoking
         * by the auth MDS. The non-auth MDS should be revoking/exporting
         * these caps, but the message is delayed.
         */
        if (ci->i_auth_cap) {
                cap = ci->i_auth_cap;
                have &= ~cap->implemented | cap->issued;
        }
        return have;
}

/*
 * Get cap bits issued by caps other than @ocap
 */
int __ceph_caps_issued_other(struct ceph_inode_info *ci, struct ceph_cap *ocap)
{
        int have = ci->i_snap_caps;
        struct ceph_cap *cap;
        struct rb_node *p;

        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (cap == ocap)
                        continue;
                if (!__cap_is_valid(cap))
                        continue;
                have |= cap->issued;
        }
        return have;
}

/*
 * Move a cap to the end of the LRU (oldest caps at list head, newest
 * at list tail).
 */
static void __touch_cap(struct ceph_cap *cap)
{
        struct ceph_mds_session *s = cap->session;

        spin_lock(&s->s_cap_lock);
        if (!s->s_cap_iterator) {
                dout("__touch_cap %p cap %p mds%d\n", &cap->ci->vfs_inode, cap,
                     s->s_mds);
                list_move_tail(&cap->session_caps, &s->s_caps);
        } else {
                dout("__touch_cap %p cap %p mds%d NOP, iterating over caps\n",
                     &cap->ci->vfs_inode, cap, s->s_mds);
        }
        spin_unlock(&s->s_cap_lock);
}

/*
 * Check if we hold the given mask.  If so, move the cap(s) to the
 * front of their respective LRUs.  (This is the preferred way for
 * callers to check for caps they want.)
 */
int __ceph_caps_issued_mask(struct ceph_inode_info *ci, int mask, int touch)
{
        struct ceph_cap *cap;
        struct rb_node *p;
        int have = ci->i_snap_caps;

        if ((have & mask) == mask) {
                dout("__ceph_caps_issued_mask ino 0x%llx snap issued %s"
                     " (mask %s)\n", ceph_ino(&ci->vfs_inode),
                     ceph_cap_string(have),
                     ceph_cap_string(mask));
                return 1;
        }

        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (!__cap_is_valid(cap))
                        continue;
                if ((cap->issued & mask) == mask) {
                        dout("__ceph_caps_issued_mask ino 0x%llx cap %p issued %s"
                             " (mask %s)\n", ceph_ino(&ci->vfs_inode), cap,
                             ceph_cap_string(cap->issued),
                             ceph_cap_string(mask));
                        if (touch)
                                __touch_cap(cap);
                        return 1;
                }

                /* does a combination of caps satisfy mask? */
                have |= cap->issued;
                if ((have & mask) == mask) {
                        dout("__ceph_caps_issued_mask ino 0x%llx combo issued %s"
                             " (mask %s)\n", ceph_ino(&ci->vfs_inode),
                             ceph_cap_string(cap->issued),
                             ceph_cap_string(mask));
                        if (touch) {
                                struct rb_node *q;

                                /* touch this + preceding caps */
                                __touch_cap(cap);
                                for (q = rb_first(&ci->i_caps); q != p;
                                     q = rb_next(q)) {
                                        cap = rb_entry(q, struct ceph_cap,
                                                       ci_node);
                                        if (!__cap_is_valid(cap))
                                                continue;
                                        if (cap->issued & mask)
                                                __touch_cap(cap);
                                }
                        }
                        return 1;
                }
        }

        return 0;
}

int __ceph_caps_issued_mask_metric(struct ceph_inode_info *ci, int mask,
                                   int touch)
{
        struct ceph_fs_client *fsc = ceph_sb_to_client(ci->vfs_inode.i_sb);
        int r;

        r = __ceph_caps_issued_mask(ci, mask, touch);
        if (r)
                ceph_update_cap_hit(&fsc->mdsc->metric);
        else
                ceph_update_cap_mis(&fsc->mdsc->metric);
        return r;
}

/*
 * Return true if mask caps are currently being revoked by an MDS.
 */
int __ceph_caps_revoking_other(struct ceph_inode_info *ci,
                               struct ceph_cap *ocap, int mask)
{
        struct ceph_cap *cap;
        struct rb_node *p;

        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (cap != ocap &&
                    (cap->implemented & ~cap->issued & mask))
                        return 1;
        }
        return 0;
}

int ceph_caps_revoking(struct ceph_inode_info *ci, int mask)
{
        struct inode *inode = &ci->vfs_inode;
        int ret;

        spin_lock(&ci->i_ceph_lock);
        ret = __ceph_caps_revoking_other(ci, NULL, mask);
        spin_unlock(&ci->i_ceph_lock);
        dout("ceph_caps_revoking %p %s = %d\n", inode,
             ceph_cap_string(mask), ret);
        return ret;
}

int __ceph_caps_used(struct ceph_inode_info *ci)
{
        int used = 0;
        if (ci->i_pin_ref)
                used |= CEPH_CAP_PIN;
        if (ci->i_rd_ref)
                used |= CEPH_CAP_FILE_RD;
        if (ci->i_rdcache_ref ||
            (S_ISREG(ci->vfs_inode.i_mode) &&
             ci->vfs_inode.i_data.nrpages))
                used |= CEPH_CAP_FILE_CACHE;
        if (ci->i_wr_ref)
                used |= CEPH_CAP_FILE_WR;
        if (ci->i_wb_ref || ci->i_wrbuffer_ref)
                used |= CEPH_CAP_FILE_BUFFER;
        if (ci->i_fx_ref)
                used |= CEPH_CAP_FILE_EXCL;
        return used;
}

#define FMODE_WAIT_BIAS 1000

/*
 * wanted, by virtue of open file modes
 */
int __ceph_caps_file_wanted(struct ceph_inode_info *ci)
{
        const int PIN_SHIFT = ffs(CEPH_FILE_MODE_PIN);
        const int RD_SHIFT = ffs(CEPH_FILE_MODE_RD);
        const int WR_SHIFT = ffs(CEPH_FILE_MODE_WR);
        const int LAZY_SHIFT = ffs(CEPH_FILE_MODE_LAZY);
        struct ceph_mount_options *opt =
                ceph_inode_to_client(&ci->vfs_inode)->mount_options;
        unsigned long used_cutoff = jiffies - opt->caps_wanted_delay_max * HZ;
        unsigned long idle_cutoff = jiffies - opt->caps_wanted_delay_min * HZ;

        if (S_ISDIR(ci->vfs_inode.i_mode)) {
                int want = 0;

                /* use used_cutoff here, to keep dir's wanted caps longer */
                if (ci->i_nr_by_mode[RD_SHIFT] > 0 ||
                    time_after(ci->i_last_rd, used_cutoff))
                        want |= CEPH_CAP_ANY_SHARED;

                if (ci->i_nr_by_mode[WR_SHIFT] > 0 ||
                    time_after(ci->i_last_wr, used_cutoff)) {
                        want |= CEPH_CAP_ANY_SHARED | CEPH_CAP_FILE_EXCL;
                        if (opt->flags & CEPH_MOUNT_OPT_ASYNC_DIROPS)
                                want |= CEPH_CAP_ANY_DIR_OPS;
                }

                if (want || ci->i_nr_by_mode[PIN_SHIFT] > 0)
                        want |= CEPH_CAP_PIN;

                return want;
        } else {
                int bits = 0;

                if (ci->i_nr_by_mode[RD_SHIFT] > 0) {
                        if (ci->i_nr_by_mode[RD_SHIFT] >= FMODE_WAIT_BIAS ||
                            time_after(ci->i_last_rd, used_cutoff))
                                bits |= 1 << RD_SHIFT;
                } else if (time_after(ci->i_last_rd, idle_cutoff)) {
                        bits |= 1 << RD_SHIFT;
                }

                if (ci->i_nr_by_mode[WR_SHIFT] > 0) {
                        if (ci->i_nr_by_mode[WR_SHIFT] >= FMODE_WAIT_BIAS ||
                            time_after(ci->i_last_wr, used_cutoff))
                                bits |= 1 << WR_SHIFT;
                } else if (time_after(ci->i_last_wr, idle_cutoff)) {
                        bits |= 1 << WR_SHIFT;
                }

                /* check lazyio only when read/write is wanted */
                if ((bits & (CEPH_FILE_MODE_RDWR << 1)) &&
                    ci->i_nr_by_mode[LAZY_SHIFT] > 0)
                        bits |= 1 << LAZY_SHIFT;

                return bits ? ceph_caps_for_mode(bits >> 1) : 0;
        }
}

/*
 * wanted, by virtue of open file modes AND cap refs (buffered/cached data)
 */
int __ceph_caps_wanted(struct ceph_inode_info *ci)
{
        int w = __ceph_caps_file_wanted(ci) | __ceph_caps_used(ci);
        if (S_ISDIR(ci->vfs_inode.i_mode)) {
                /* we want EXCL if holding caps of dir ops */
                if (w & CEPH_CAP_ANY_DIR_OPS)
                        w |= CEPH_CAP_FILE_EXCL;
        } else {
                /* we want EXCL if dirty data */
                if (w & CEPH_CAP_FILE_BUFFER)
                        w |= CEPH_CAP_FILE_EXCL;
        }
        return w;
}

/*
 * Return caps we have registered with the MDS(s) as 'wanted'.
 */
int __ceph_caps_mds_wanted(struct ceph_inode_info *ci, bool check)
{
        struct ceph_cap *cap;
        struct rb_node *p;
        int mds_wanted = 0;

        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (check && !__cap_is_valid(cap))
                        continue;
                if (cap == ci->i_auth_cap)
                        mds_wanted |= cap->mds_wanted;
                else
                        mds_wanted |= (cap->mds_wanted & ~CEPH_CAP_ANY_FILE_WR);
        }
        return mds_wanted;
}

int ceph_is_any_caps(struct inode *inode)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        int ret;

        spin_lock(&ci->i_ceph_lock);
        ret = __ceph_is_any_real_caps(ci);
        spin_unlock(&ci->i_ceph_lock);

        return ret;
}

static void drop_inode_snap_realm(struct ceph_inode_info *ci)
{
        struct ceph_snap_realm *realm = ci->i_snap_realm;
        spin_lock(&realm->inodes_with_caps_lock);
        list_del_init(&ci->i_snap_realm_item);
        ci->i_snap_realm_counter++;
        ci->i_snap_realm = NULL;
        if (realm->ino == ci->i_vino.ino)
                realm->inode = NULL;
        spin_unlock(&realm->inodes_with_caps_lock);
        ceph_put_snap_realm(ceph_sb_to_client(ci->vfs_inode.i_sb)->mdsc,
                            realm);
}

/*
 * Remove a cap.  Take steps to deal with a racing iterate_session_caps.
 *
 * caller should hold i_ceph_lock.
 * caller will not hold session s_mutex if called from destroy_inode.
 */
void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release)
{
        struct ceph_mds_session *session = cap->session;
        struct ceph_inode_info *ci = cap->ci;
        struct ceph_mds_client *mdsc;
        int removed = 0;

        /* 'ci' being NULL means the remove have already occurred */
        if (!ci) {
                dout("%s: cap inode is NULL\n", __func__);
                return;
        }

        dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode);

        mdsc = ceph_inode_to_client(&ci->vfs_inode)->mdsc;

        /* remove from inode's cap rbtree, and clear auth cap */
        rb_erase(&cap->ci_node, &ci->i_caps);
        if (ci->i_auth_cap == cap) {
                WARN_ON_ONCE(!list_empty(&ci->i_dirty_item) &&
                             !mdsc->fsc->blocklisted);
                ci->i_auth_cap = NULL;
        }

        /* remove from session list */
        spin_lock(&session->s_cap_lock);
        if (session->s_cap_iterator == cap) {
                /* not yet, we are iterating over this very cap */
                dout("__ceph_remove_cap  delaying %p removal from session %p\n",
                     cap, cap->session);
        } else {
                list_del_init(&cap->session_caps);
                session->s_nr_caps--;
                atomic64_dec(&mdsc->metric.total_caps);
                cap->session = NULL;
                removed = 1;
        }
        /* protect backpointer with s_cap_lock: see iterate_session_caps */
        cap->ci = NULL;

        /*
         * s_cap_reconnect is protected by s_cap_lock. no one changes
         * s_cap_gen while session is in the reconnect state.
         */
        if (queue_release &&
            (!session->s_cap_reconnect ||
             cap->cap_gen == atomic_read(&session->s_cap_gen))) {
                cap->queue_release = 1;
                if (removed) {
                        __ceph_queue_cap_release(session, cap);
                        removed = 0;
                }
        } else {
                cap->queue_release = 0;
        }
        cap->cap_ino = ci->i_vino.ino;

        spin_unlock(&session->s_cap_lock);

        if (removed)
                ceph_put_cap(mdsc, cap);

        if (!__ceph_is_any_real_caps(ci)) {
                /* when reconnect denied, we remove session caps forcibly,
                 * i_wr_ref can be non-zero. If there are ongoing write,
                 * keep i_snap_realm.
                 */
                if (ci->i_wr_ref == 0 && ci->i_snap_realm)
                        drop_inode_snap_realm(ci);

                __cap_delay_cancel(mdsc, ci);
        }
}

struct cap_msg_args {
        struct ceph_mds_session *session;
        u64                     ino, cid, follows;
        u64                     flush_tid, oldest_flush_tid, size, max_size;
        u64                     xattr_version;
        u64                     change_attr;
        struct ceph_buffer      *xattr_buf;
        struct ceph_buffer      *old_xattr_buf;
        struct timespec64       atime, mtime, ctime, btime;
        int                     op, caps, wanted, dirty;
        u32                     seq, issue_seq, mseq, time_warp_seq;
        u32                     flags;
        kuid_t                  uid;
        kgid_t                  gid;
        umode_t                 mode;
        bool                    inline_data;
        bool                    wake;
};

/*
 * cap struct size + flock buffer size + inline version + inline data size +
 * osd_epoch_barrier + oldest_flush_tid
 */
#define CAP_MSG_SIZE (sizeof(struct ceph_mds_caps) + \
                      4 + 8 + 4 + 4 + 8 + 4 + 4 + 4 + 8 + 8 + 4)

/* Marshal up the cap msg to the MDS */
static void encode_cap_msg(struct ceph_msg *msg, struct cap_msg_args *arg)
{
        struct ceph_mds_caps *fc;
        void *p;
        struct ceph_osd_client *osdc = &arg->session->s_mdsc->fsc->client->osdc;

        dout("%s %s %llx %llx caps %s wanted %s dirty %s seq %u/%u tid %llu/%llu mseq %u follows %lld size %llu/%llu xattr_ver %llu xattr_len %d\n",
             __func__, ceph_cap_op_name(arg->op), arg->cid, arg->ino,
             ceph_cap_string(arg->caps), ceph_cap_string(arg->wanted),
             ceph_cap_string(arg->dirty), arg->seq, arg->issue_seq,
             arg->flush_tid, arg->oldest_flush_tid, arg->mseq, arg->follows,
             arg->size, arg->max_size, arg->xattr_version,
             arg->xattr_buf ? (int)arg->xattr_buf->vec.iov_len : 0);

        msg->hdr.version = cpu_to_le16(10);
        msg->hdr.tid = cpu_to_le64(arg->flush_tid);

        fc = msg->front.iov_base;
        memset(fc, 0, sizeof(*fc));

        fc->cap_id = cpu_to_le64(arg->cid);
        fc->op = cpu_to_le32(arg->op);
        fc->seq = cpu_to_le32(arg->seq);
        fc->issue_seq = cpu_to_le32(arg->issue_seq);
        fc->migrate_seq = cpu_to_le32(arg->mseq);
        fc->caps = cpu_to_le32(arg->caps);
        fc->wanted = cpu_to_le32(arg->wanted);
        fc->dirty = cpu_to_le32(arg->dirty);
        fc->ino = cpu_to_le64(arg->ino);
        fc->snap_follows = cpu_to_le64(arg->follows);

        fc->size = cpu_to_le64(arg->size);
        fc->max_size = cpu_to_le64(arg->max_size);
        ceph_encode_timespec64(&fc->mtime, &arg->mtime);
        ceph_encode_timespec64(&fc->atime, &arg->atime);
        ceph_encode_timespec64(&fc->ctime, &arg->ctime);
        fc->time_warp_seq = cpu_to_le32(arg->time_warp_seq);

        fc->uid = cpu_to_le32(from_kuid(&init_user_ns, arg->uid));
        fc->gid = cpu_to_le32(from_kgid(&init_user_ns, arg->gid));
        fc->mode = cpu_to_le32(arg->mode);

        fc->xattr_version = cpu_to_le64(arg->xattr_version);
        if (arg->xattr_buf) {
                msg->middle = ceph_buffer_get(arg->xattr_buf);
                fc->xattr_len = cpu_to_le32(arg->xattr_buf->vec.iov_len);
                msg->hdr.middle_len = cpu_to_le32(arg->xattr_buf->vec.iov_len);
        }

        p = fc + 1;
        /* flock buffer size (version 2) */
        ceph_encode_32(&p, 0);
        /* inline version (version 4) */
        ceph_encode_64(&p, arg->inline_data ? 0 : CEPH_INLINE_NONE);
        /* inline data size */
        ceph_encode_32(&p, 0);
        /*
         * osd_epoch_barrier (version 5)
         * The epoch_barrier is protected osdc->lock, so READ_ONCE here in
         * case it was recently changed
         */
        ceph_encode_32(&p, READ_ONCE(osdc->epoch_barrier));
        /* oldest_flush_tid (version 6) */
        ceph_encode_64(&p, arg->oldest_flush_tid);

        /*
         * caller_uid/caller_gid (version 7)
         *
         * Currently, we don't properly track which caller dirtied the caps
         * last, and force a flush of them when there is a conflict. For now,
         * just set this to 0:0, to emulate how the MDS has worked up to now.
         */
        ceph_encode_32(&p, 0);
        ceph_encode_32(&p, 0);

        /* pool namespace (version 8) (mds always ignores this) */
        ceph_encode_32(&p, 0);

        /* btime and change_attr (version 9) */
        ceph_encode_timespec64(p, &arg->btime);
        p += sizeof(struct ceph_timespec);
        ceph_encode_64(&p, arg->change_attr);

        /* Advisory flags (version 10) */
        ceph_encode_32(&p, arg->flags);
}

/*
 * Queue cap releases when an inode is dropped from our cache.
 */
void __ceph_remove_caps(struct ceph_inode_info *ci)
{
        struct rb_node *p;

        /* lock i_ceph_lock, because ceph_d_revalidate(..., LOOKUP_RCU)
         * may call __ceph_caps_issued_mask() on a freeing inode. */
        spin_lock(&ci->i_ceph_lock);
        p = rb_first(&ci->i_caps);
        while (p) {
                struct ceph_cap *cap = rb_entry(p, struct ceph_cap, ci_node);
                p = rb_next(p);
                __ceph_remove_cap(cap, true);
        }
        spin_unlock(&ci->i_ceph_lock);
}

/*
 * Prepare to send a cap message to an MDS. Update the cap state, and populate
 * the arg struct with the parameters that will need to be sent. This should
 * be done under the i_ceph_lock to guard against changes to cap state.
 *
 * Make note of max_size reported/requested from mds, revoked caps
 * that have now been implemented.
 */
static void __prep_cap(struct cap_msg_args *arg, struct ceph_cap *cap,
                       int op, int flags, int used, int want, int retain,
                       int flushing, u64 flush_tid, u64 oldest_flush_tid)
{
        struct ceph_inode_info *ci = cap->ci;
        struct inode *inode = &ci->vfs_inode;
        int held, revoking;

        lockdep_assert_held(&ci->i_ceph_lock);

        held = cap->issued | cap->implemented;
        revoking = cap->implemented & ~cap->issued;
        retain &= ~revoking;

        dout("%s %p cap %p session %p %s -> %s (revoking %s)\n",
             __func__, inode, cap, cap->session,
             ceph_cap_string(held), ceph_cap_string(held & retain),
             ceph_cap_string(revoking));
        BUG_ON((retain & CEPH_CAP_PIN) == 0);

        ci->i_ceph_flags &= ~CEPH_I_FLUSH;

        cap->issued &= retain;  /* drop bits we don't want */
        /*
         * Wake up any waiters on wanted -> needed transition. This is due to
         * the weird transition from buffered to sync IO... we need to flush
         * dirty pages _before_ allowing sync writes to avoid reordering.
         */
        arg->wake = cap->implemented & ~cap->issued;
        cap->implemented &= cap->issued | used;
        cap->mds_wanted = want;

        arg->session = cap->session;
        arg->ino = ceph_vino(inode).ino;
        arg->cid = cap->cap_id;
        arg->follows = flushing ? ci->i_head_snapc->seq : 0;
        arg->flush_tid = flush_tid;
        arg->oldest_flush_tid = oldest_flush_tid;

        arg->size = i_size_read(inode);
        ci->i_reported_size = arg->size;
        arg->max_size = ci->i_wanted_max_size;
        if (cap == ci->i_auth_cap) {
                if (want & CEPH_CAP_ANY_FILE_WR)
                        ci->i_requested_max_size = arg->max_size;
                else
                        ci->i_requested_max_size = 0;
        }

        if (flushing & CEPH_CAP_XATTR_EXCL) {
                arg->old_xattr_buf = __ceph_build_xattrs_blob(ci);
                arg->xattr_version = ci->i_xattrs.version;
                arg->xattr_buf = ci->i_xattrs.blob;
        } else {
                arg->xattr_buf = NULL;
                arg->old_xattr_buf = NULL;
        }

        arg->mtime = inode->i_mtime;
        arg->atime = inode->i_atime;
        arg->ctime = inode->i_ctime;
        arg->btime = ci->i_btime;
        arg->change_attr = inode_peek_iversion_raw(inode);

        arg->op = op;
        arg->caps = cap->implemented;
        arg->wanted = want;
        arg->dirty = flushing;

        arg->seq = cap->seq;
        arg->issue_seq = cap->issue_seq;
        arg->mseq = cap->mseq;
        arg->time_warp_seq = ci->i_time_warp_seq;

        arg->uid = inode->i_uid;
        arg->gid = inode->i_gid;
        arg->mode = inode->i_mode;

        arg->inline_data = ci->i_inline_version != CEPH_INLINE_NONE;
        if (!(flags & CEPH_CLIENT_CAPS_PENDING_CAPSNAP) &&
            !list_empty(&ci->i_cap_snaps)) {
                struct ceph_cap_snap *capsnap;
                list_for_each_entry_reverse(capsnap, &ci->i_cap_snaps, ci_item) {
                        if (capsnap->cap_flush.tid)
                                break;
                        if (capsnap->need_flush) {
                                flags |= CEPH_CLIENT_CAPS_PENDING_CAPSNAP;
                                break;
                        }
                }
        }
        arg->flags = flags;
}

/*
 * Send a cap msg on the given inode.
 *
 * Caller should hold snap_rwsem (read), s_mutex.
 */
static void __send_cap(struct cap_msg_args *arg, struct ceph_inode_info *ci)
{
        struct ceph_msg *msg;
        struct inode *inode = &ci->vfs_inode;

        msg = ceph_msg_new(CEPH_MSG_CLIENT_CAPS, CAP_MSG_SIZE, GFP_NOFS, false);
        if (!msg) {
                pr_err("error allocating cap msg: ino (%llx.%llx) flushing %s tid %llu, requeuing cap.\n",
                       ceph_vinop(inode), ceph_cap_string(arg->dirty),
                       arg->flush_tid);
                spin_lock(&ci->i_ceph_lock);
                __cap_delay_requeue(arg->session->s_mdsc, ci);
                spin_unlock(&ci->i_ceph_lock);
                return;
        }

        encode_cap_msg(msg, arg);
        ceph_con_send(&arg->session->s_con, msg);
        ceph_buffer_put(arg->old_xattr_buf);
        if (arg->wake)
                wake_up_all(&ci->i_cap_wq);
}

static inline int __send_flush_snap(struct inode *inode,
                                    struct ceph_mds_session *session,
                                    struct ceph_cap_snap *capsnap,
                                    u32 mseq, u64 oldest_flush_tid)
{
        struct cap_msg_args     arg;
        struct ceph_msg         *msg;

        msg = ceph_msg_new(CEPH_MSG_CLIENT_CAPS, CAP_MSG_SIZE, GFP_NOFS, false);
        if (!msg)
                return -ENOMEM;

        arg.session = session;
        arg.ino = ceph_vino(inode).ino;
        arg.cid = 0;
        arg.follows = capsnap->follows;
        arg.flush_tid = capsnap->cap_flush.tid;
        arg.oldest_flush_tid = oldest_flush_tid;

        arg.size = capsnap->size;
        arg.max_size = 0;
        arg.xattr_version = capsnap->xattr_version;
        arg.xattr_buf = capsnap->xattr_blob;
        arg.old_xattr_buf = NULL;

        arg.atime = capsnap->atime;
        arg.mtime = capsnap->mtime;
        arg.ctime = capsnap->ctime;
        arg.btime = capsnap->btime;
        arg.change_attr = capsnap->change_attr;

        arg.op = CEPH_CAP_OP_FLUSHSNAP;
        arg.caps = capsnap->issued;
        arg.wanted = 0;
        arg.dirty = capsnap->dirty;

        arg.seq = 0;
        arg.issue_seq = 0;
        arg.mseq = mseq;
        arg.time_warp_seq = capsnap->time_warp_seq;

        arg.uid = capsnap->uid;
        arg.gid = capsnap->gid;
        arg.mode = capsnap->mode;

        arg.inline_data = capsnap->inline_data;
        arg.flags = 0;
        arg.wake = false;

        encode_cap_msg(msg, &arg);
        ceph_con_send(&arg.session->s_con, msg);
        return 0;
}

/*
 * When a snapshot is taken, clients accumulate dirty metadata on
 * inodes with capabilities in ceph_cap_snaps to describe the file
 * state at the time the snapshot was taken.  This must be flushed
 * asynchronously back to the MDS once sync writes complete and dirty
 * data is written out.
 *
 * Called under i_ceph_lock.
 */
static void __ceph_flush_snaps(struct ceph_inode_info *ci,
                               struct ceph_mds_session *session)
                __releases(ci->i_ceph_lock)
                __acquires(ci->i_ceph_lock)
{
        struct inode *inode = &ci->vfs_inode;
        struct ceph_mds_client *mdsc = session->s_mdsc;
        struct ceph_cap_snap *capsnap;
        u64 oldest_flush_tid = 0;
        u64 first_tid = 1, last_tid = 0;

        dout("__flush_snaps %p session %p\n", inode, session);

        list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
                /*
                 * we need to wait for sync writes to complete and for dirty
                 * pages to be written out.
                 */
                if (capsnap->dirty_pages || capsnap->writing)
                        break;

                /* should be removed by ceph_try_drop_cap_snap() */
                BUG_ON(!capsnap->need_flush);

                /* only flush each capsnap once */
                if (capsnap->cap_flush.tid > 0) {
                        dout(" already flushed %p, skipping\n", capsnap);
                        continue;
                }

                spin_lock(&mdsc->cap_dirty_lock);
                capsnap->cap_flush.tid = ++mdsc->last_cap_flush_tid;
                list_add_tail(&capsnap->cap_flush.g_list,
                              &mdsc->cap_flush_list);
                if (oldest_flush_tid == 0)
                        oldest_flush_tid = __get_oldest_flush_tid(mdsc);
                if (list_empty(&ci->i_flushing_item)) {
                        list_add_tail(&ci->i_flushing_item,
                                      &session->s_cap_flushing);
                }
                spin_unlock(&mdsc->cap_dirty_lock);

                list_add_tail(&capsnap->cap_flush.i_list,
                              &ci->i_cap_flush_list);

                if (first_tid == 1)
                        first_tid = capsnap->cap_flush.tid;
                last_tid = capsnap->cap_flush.tid;
        }

        ci->i_ceph_flags &= ~CEPH_I_FLUSH_SNAPS;

        while (first_tid <= last_tid) {
                struct ceph_cap *cap = ci->i_auth_cap;
                struct ceph_cap_flush *cf;
                int ret;

                if (!(cap && cap->session == session)) {
                        dout("__flush_snaps %p auth cap %p not mds%d, "
                             "stop\n", inode, cap, session->s_mds);
                        break;
                }

                ret = -ENOENT;
                list_for_each_entry(cf, &ci->i_cap_flush_list, i_list) {
                        if (cf->tid >= first_tid) {
                                ret = 0;
                                break;
                        }
                }
                if (ret < 0)
                        break;

                first_tid = cf->tid + 1;

                capsnap = container_of(cf, struct ceph_cap_snap, cap_flush);
                refcount_inc(&capsnap->nref);
                spin_unlock(&ci->i_ceph_lock);

                dout("__flush_snaps %p capsnap %p tid %llu %s\n",
                     inode, capsnap, cf->tid, ceph_cap_string(capsnap->dirty));

                ret = __send_flush_snap(inode, session, capsnap, cap->mseq,
                                        oldest_flush_tid);
                if (ret < 0) {
                        pr_err("__flush_snaps: error sending cap flushsnap, "
                               "ino (%llx.%llx) tid %llu follows %llu\n",
                                ceph_vinop(inode), cf->tid, capsnap->follows);
                }

                ceph_put_cap_snap(capsnap);
                spin_lock(&ci->i_ceph_lock);
        }
}

void ceph_flush_snaps(struct ceph_inode_info *ci,
                      struct ceph_mds_session **psession)
{
        struct inode *inode = &ci->vfs_inode;
        struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
        struct ceph_mds_session *session = NULL;
        int mds;

        dout("ceph_flush_snaps %p\n", inode);
        if (psession)
                session = *psession;
retry:
        spin_lock(&ci->i_ceph_lock);
        if (!(ci->i_ceph_flags & CEPH_I_FLUSH_SNAPS)) {
                dout(" no capsnap needs flush, doing nothing\n");
                goto out;
        }
        if (!ci->i_auth_cap) {
                dout(" no auth cap (migrating?), doing nothing\n");
                goto out;
        }

        mds = ci->i_auth_cap->session->s_mds;
        if (session && session->s_mds != mds) {
                dout(" oops, wrong session %p mutex\n", session);
                ceph_put_mds_session(session);
                session = NULL;
        }
        if (!session) {
                spin_unlock(&ci->i_ceph_lock);
                mutex_lock(&mdsc->mutex);
                session = __ceph_lookup_mds_session(mdsc, mds);
                mutex_unlock(&mdsc->mutex);
                goto retry;
        }

        // make sure flushsnap messages are sent in proper order.
        if (ci->i_ceph_flags & CEPH_I_KICK_FLUSH)
                __kick_flushing_caps(mdsc, session, ci, 0);

        __ceph_flush_snaps(ci, session);
out:
        spin_unlock(&ci->i_ceph_lock);

        if (psession)
                *psession = session;
        else
                ceph_put_mds_session(session);
        /* we flushed them all; remove this inode from the queue */
        spin_lock(&mdsc->snap_flush_lock);
        list_del_init(&ci->i_snap_flush_item);
        spin_unlock(&mdsc->snap_flush_lock);
}

/*
 * Mark caps dirty.  If inode is newly dirty, return the dirty flags.
 * Caller is then responsible for calling __mark_inode_dirty with the
 * returned flags value.
 */
int __ceph_mark_dirty_caps(struct ceph_inode_info *ci, int mask,
                           struct ceph_cap_flush **pcf)
{
        struct ceph_mds_client *mdsc =
                ceph_sb_to_client(ci->vfs_inode.i_sb)->mdsc;
        struct inode *inode = &ci->vfs_inode;
        int was = ci->i_dirty_caps;
        int dirty = 0;

        lockdep_assert_held(&ci->i_ceph_lock);

        if (!ci->i_auth_cap) {
                pr_warn("__mark_dirty_caps %p %llx mask %s, "
                        "but no auth cap (session was closed?)\n",
                        inode, ceph_ino(inode), ceph_cap_string(mask));
                return 0;
        }

        dout("__mark_dirty_caps %p %s dirty %s -> %s\n", &ci->vfs_inode,
             ceph_cap_string(mask), ceph_cap_string(was),
             ceph_cap_string(was | mask));
        ci->i_dirty_caps |= mask;
        if (was == 0) {
                struct ceph_mds_session *session = ci->i_auth_cap->session;

                WARN_ON_ONCE(ci->i_prealloc_cap_flush);
                swap(ci->i_prealloc_cap_flush, *pcf);

                if (!ci->i_head_snapc) {
                        WARN_ON_ONCE(!rwsem_is_locked(&mdsc->snap_rwsem));
                        ci->i_head_snapc = ceph_get_snap_context(
                                ci->i_snap_realm->cached_context);
                }
                dout(" inode %p now dirty snapc %p auth cap %p\n",
                     &ci->vfs_inode, ci->i_head_snapc, ci->i_auth_cap);
                BUG_ON(!list_empty(&ci->i_dirty_item));
                spin_lock(&mdsc->cap_dirty_lock);
                list_add(&ci->i_dirty_item, &session->s_cap_dirty);
                spin_unlock(&mdsc->cap_dirty_lock);
                if (ci->i_flushing_caps == 0) {
                        ihold(inode);
                        dirty |= I_DIRTY_SYNC;
                }
        } else {
                WARN_ON_ONCE(!ci->i_prealloc_cap_flush);
        }
        BUG_ON(list_empty(&ci->i_dirty_item));
        if (((was | ci->i_flushing_caps) & CEPH_CAP_FILE_BUFFER) &&
            (mask & CEPH_CAP_FILE_BUFFER))
                dirty |= I_DIRTY_DATASYNC;
        __cap_delay_requeue(mdsc, ci);
        return dirty;
}

struct ceph_cap_flush *ceph_alloc_cap_flush(void)
{
        struct ceph_cap_flush *cf;

        cf = kmem_cache_alloc(ceph_cap_flush_cachep, GFP_KERNEL);
        cf->is_capsnap = false;
        return cf;
}

void ceph_free_cap_flush(struct ceph_cap_flush *cf)
{
        if (cf)
                kmem_cache_free(ceph_cap_flush_cachep, cf);
}

static u64 __get_oldest_flush_tid(struct ceph_mds_client *mdsc)
{
        if (!list_empty(&mdsc->cap_flush_list)) {
                struct ceph_cap_flush *cf =
                        list_first_entry(&mdsc->cap_flush_list,
                                         struct ceph_cap_flush, g_list);
                return cf->tid;
        }
        return 0;
}

/*
 * Remove cap_flush from the mdsc's or inode's flushing cap list.
 * Return true if caller needs to wake up flush waiters.
 */
static bool __detach_cap_flush_from_mdsc(struct ceph_mds_client *mdsc,
                                         struct ceph_cap_flush *cf)
{
        struct ceph_cap_flush *prev;
        bool wake = cf->wake;

        if (wake && cf->g_list.prev != &mdsc->cap_flush_list) {
                prev = list_prev_entry(cf, g_list);
                prev->wake = true;
                wake = false;
        }
        list_del_init(&cf->g_list);
        return wake;
}

static bool __detach_cap_flush_from_ci(struct ceph_inode_info *ci,
                                       struct ceph_cap_flush *cf)
{
        struct ceph_cap_flush *prev;
        bool wake = cf->wake;

        if (wake && cf->i_list.prev != &ci->i_cap_flush_list) {
                prev = list_prev_entry(cf, i_list);
                prev->wake = true;
                wake = false;
        }
        list_del_init(&cf->i_list);
        return wake;
}

/*
 * Add dirty inode to the flushing list.  Assigned a seq number so we
 * can wait for caps to flush without starving.
 *
 * Called under i_ceph_lock. Returns the flush tid.
 */
static u64 __mark_caps_flushing(struct inode *inode,
                                struct ceph_mds_session *session, bool wake,
                                u64 *oldest_flush_tid)
{
        struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc;
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_cap_flush *cf = NULL;
        int flushing;

        lockdep_assert_held(&ci->i_ceph_lock);
        BUG_ON(ci->i_dirty_caps == 0);
        BUG_ON(list_empty(&ci->i_dirty_item));
        BUG_ON(!ci->i_prealloc_cap_flush);

        flushing = ci->i_dirty_caps;
        dout("__mark_caps_flushing flushing %s, flushing_caps %s -> %s\n",
             ceph_cap_string(flushing),
             ceph_cap_string(ci->i_flushing_caps),
             ceph_cap_string(ci->i_flushing_caps | flushing));
        ci->i_flushing_caps |= flushing;
        ci->i_dirty_caps = 0;
        dout(" inode %p now !dirty\n", inode);

        swap(cf, ci->i_prealloc_cap_flush);
        cf->caps = flushing;
        cf->wake = wake;

        spin_lock(&mdsc->cap_dirty_lock);
        list_del_init(&ci->i_dirty_item);

        cf->tid = ++mdsc->last_cap_flush_tid;
        list_add_tail(&cf->g_list, &mdsc->cap_flush_list);
        *oldest_flush_tid = __get_oldest_flush_tid(mdsc);

        if (list_empty(&ci->i_flushing_item)) {
                list_add_tail(&ci->i_flushing_item, &session->s_cap_flushing);
                mdsc->num_cap_flushing++;
        }
        spin_unlock(&mdsc->cap_dirty_lock);

        list_add_tail(&cf->i_list, &ci->i_cap_flush_list);

        return cf->tid;
}

/*
 * try to invalidate mapping pages without blocking.
 */
static int try_nonblocking_invalidate(struct inode *inode)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        u32 invalidating_gen = ci->i_rdcache_gen;

        spin_unlock(&ci->i_ceph_lock);
        ceph_fscache_invalidate(inode);
        invalidate_mapping_pages(&inode->i_data, 0, -1);
        spin_lock(&ci->i_ceph_lock);

        if (inode->i_data.nrpages == 0 &&
            invalidating_gen == ci->i_rdcache_gen) {
                /* success. */
                dout("try_nonblocking_invalidate %p success\n", inode);
                /* save any racing async invalidate some trouble */
                ci->i_rdcache_revoking = ci->i_rdcache_gen - 1;
                return 0;
        }
        dout("try_nonblocking_invalidate %p failed\n", inode);
        return -1;
}

bool __ceph_should_report_size(struct ceph_inode_info *ci)
{
        loff_t size = i_size_read(&ci->vfs_inode);
        /* mds will adjust max size according to the reported size */
        if (ci->i_flushing_caps & CEPH_CAP_FILE_WR)
                return false;
        if (size >= ci->i_max_size)
                return true;
        /* half of previous max_size increment has been used */
        if (ci->i_max_size > ci->i_reported_size &&
            (size << 1) >= ci->i_max_size + ci->i_reported_size)
                return true;
        return false;
}

/*
 * Swiss army knife function to examine currently used and wanted
 * versus held caps.  Release, flush, ack revoked caps to mds as
 * appropriate.
 *
 *  CHECK_CAPS_AUTHONLY - we should only check the auth cap
 *  CHECK_CAPS_FLUSH - we should flush any dirty caps immediately, without
 *    further delay.
 */
void ceph_check_caps(struct ceph_inode_info *ci, int flags,
                     struct ceph_mds_session *session)
{
        struct inode *inode = &ci->vfs_inode;
        struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(inode->i_sb);
        struct ceph_cap *cap;
        u64 flush_tid, oldest_flush_tid;
        int file_wanted, used, cap_used;
        int issued, implemented, want, retain, revoking, flushing = 0;
        int mds = -1;   /* keep track of how far we've gone through i_caps list
                           to avoid an infinite loop on retry */
        struct rb_node *p;
        bool queue_invalidate = false;
        bool tried_invalidate = false;

        if (session)
                ceph_get_mds_session(session);

        spin_lock(&ci->i_ceph_lock);
        if (ci->i_ceph_flags & CEPH_I_FLUSH)
                flags |= CHECK_CAPS_FLUSH;
retry:
        /* Caps wanted by virtue of active open files. */
        file_wanted = __ceph_caps_file_wanted(ci);

        /* Caps which have active references against them */
        used = __ceph_caps_used(ci);

        /*
         * "issued" represents the current caps that the MDS wants us to have.
         * "implemented" is the set that we have been granted, and includes the
         * ones that have not yet been returned to the MDS (the "revoking" set,
         * usually because they have outstanding references).
         */
        issued = __ceph_caps_issued(ci, &implemented);
        revoking = implemented & ~issued;

        want = file_wanted;

        /* The ones we currently want to retain (may be adjusted below) */
        retain = file_wanted | used | CEPH_CAP_PIN;
        if (!mdsc->stopping && inode->i_nlink > 0) {
                if (file_wanted) {
                        retain |= CEPH_CAP_ANY;       /* be greedy */
                } else if (S_ISDIR(inode->i_mode) &&
                           (issued & CEPH_CAP_FILE_SHARED) &&
                           __ceph_dir_is_complete(ci)) {
                        /*
                         * If a directory is complete, we want to keep
                         * the exclusive cap. So that MDS does not end up
                         * revoking the shared cap on every create/unlink
                         * operation.
                         */
                        if (IS_RDONLY(inode)) {
                                want = CEPH_CAP_ANY_SHARED;
                        } else {
                                want |= CEPH_CAP_ANY_SHARED | CEPH_CAP_FILE_EXCL;
                        }
                        retain |= want;
                } else {

                        retain |= CEPH_CAP_ANY_SHARED;
                        /*
                         * keep RD only if we didn't have the file open RW,
                         * because then the mds would revoke it anyway to
                         * journal max_size=0.
                         */
                        if (ci->i_max_size == 0)
                                retain |= CEPH_CAP_ANY_RD;
                }
        }

        dout("check_caps %p file_want %s used %s dirty %s flushing %s"
             " issued %s revoking %s retain %s %s%s\n", inode,
             ceph_cap_string(file_wanted),
             ceph_cap_string(used), ceph_cap_string(ci->i_dirty_caps),
             ceph_cap_string(ci->i_flushing_caps),
             ceph_cap_string(issued), ceph_cap_string(revoking),
             ceph_cap_string(retain),
             (flags & CHECK_CAPS_AUTHONLY) ? " AUTHONLY" : "",
             (flags & CHECK_CAPS_FLUSH) ? " FLUSH" : "");

        /*
         * If we no longer need to hold onto old our caps, and we may
         * have cached pages, but don't want them, then try to invalidate.
         * If we fail, it's because pages are locked.... try again later.
         */
        if ((!(flags & CHECK_CAPS_NOINVAL) || mdsc->stopping) &&
            S_ISREG(inode->i_mode) &&
            !(ci->i_wb_ref || ci->i_wrbuffer_ref) &&   /* no dirty pages... */
            inode->i_data.nrpages &&            /* have cached pages */
            (revoking & (CEPH_CAP_FILE_CACHE|
                         CEPH_CAP_FILE_LAZYIO)) && /*  or revoking cache */
            !tried_invalidate) {
                dout("check_caps trying to invalidate on %p\n", inode);
                if (try_nonblocking_invalidate(inode) < 0) {
                        dout("check_caps queuing invalidate\n");