/*
 * linux/fs/nfs/read.c
 *
 * Block I/O for NFS
 *
 * Partial copy of Linus' read cache modifications to fs/nfs/file.c
 * modified for async RPC by okir@monad.swb.de
 */

#include <linux/time.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/stat.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/sunrpc/clnt.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_page.h>
#include <linux/module.h>

#include <asm/system.h>
#include "pnfs.h"

#include "nfs4_fs.h"
#include "internal.h"
#include "iostat.h"
#include "fscache.h"

#define NFSDBG_FACILITY         NFSDBG_PAGECACHE

static const struct nfs_pageio_ops nfs_pageio_read_ops;
static const struct rpc_call_ops nfs_read_partial_ops;
static const struct rpc_call_ops nfs_read_full_ops;

static struct kmem_cache *nfs_rdata_cachep;

struct nfs_read_data *nfs_readdata_alloc(unsigned int pagecount)
{
        struct nfs_read_data *p;

        p = kmem_cache_zalloc(nfs_rdata_cachep, GFP_KERNEL);
        if (p) {
                INIT_LIST_HEAD(&p->pages);
                p->npages = pagecount;
                if (pagecount <= ARRAY_SIZE(p->page_array))
                        p->pagevec = p->page_array;
                else {
                        p->pagevec = kcalloc(pagecount, sizeof(struct page *), GFP_KERNEL);
                        if (!p->pagevec) {
                                kmem_cache_free(nfs_rdata_cachep, p);
                                p = NULL;
                        }
                }
        }
        return p;
}

void nfs_readdata_free(struct nfs_read_data *p)
{
        if (p && (p->pagevec != &p->page_array[0]))
                kfree(p->pagevec);
        kmem_cache_free(nfs_rdata_cachep, p);
}

void nfs_readdata_release(struct nfs_read_data *rdata)
{
        put_lseg(rdata->lseg);
        put_nfs_open_context(rdata->args.context);
        nfs_readdata_free(rdata);
}

static
int nfs_return_empty_page(struct page *page)
{
        zero_user(page, 0, PAGE_CACHE_SIZE);
        SetPageUptodate(page);
        unlock_page(page);
        return 0;
}

static void nfs_readpage_truncate_uninitialised_page(struct nfs_read_data *data)
{
        unsigned int remainder = data->args.count - data->res.count;
        unsigned int base = data->args.pgbase + data->res.count;
        unsigned int pglen;
        struct page **pages;

        if (data->res.eof == 0 || remainder == 0)
                return;
        /*
         * Note: "remainder" can never be negative, since we check for
         *      this in the XDR code.
         */
        pages = &data->args.pages[base >> PAGE_CACHE_SHIFT];
        base &= ~PAGE_CACHE_MASK;
        pglen = PAGE_CACHE_SIZE - base;
        for (;;) {
                if (remainder <= pglen) {
                        zero_user(*pages, base, remainder);
                        break;
                }
                zero_user(*pages, base, pglen);
                pages++;
                remainder -= pglen;
                pglen = PAGE_CACHE_SIZE;
                base = 0;
        }
}

void nfs_pageio_init_read_mds(struct nfs_pageio_descriptor *pgio,
                struct inode *inode)
{
        nfs_pageio_init(pgio, inode, &nfs_pageio_read_ops,
                        NFS_SERVER(inode)->rsize, 0);
}

void nfs_pageio_reset_read_mds(struct nfs_pageio_descriptor *pgio)
{
        pgio->pg_ops = &nfs_pageio_read_ops;
        pgio->pg_bsize = NFS_SERVER(pgio->pg_inode)->rsize;
}
EXPORT_SYMBOL_GPL(nfs_pageio_reset_read_mds);

static void nfs_pageio_init_read(struct nfs_pageio_descriptor *pgio,
                struct inode *inode)
{
        if (!pnfs_pageio_init_read(pgio, inode))
                nfs_pageio_init_read_mds(pgio, inode);
}

int nfs_readpage_async(struct nfs_open_context *ctx, struct inode *inode,
                       struct page *page)
{
        struct nfs_page *new;
        unsigned int len;
        struct nfs_pageio_descriptor pgio;

        len = nfs_page_length(page);
        if (len == 0)
                return nfs_return_empty_page(page);
        new = nfs_create_request(ctx, inode, page, 0, len);
        if (IS_ERR(new)) {
                unlock_page(page);
                return PTR_ERR(new);
        }
        if (len < PAGE_CACHE_SIZE)
                zero_user_segment(page, len, PAGE_CACHE_SIZE);

        nfs_pageio_init_read(&pgio, inode);
        nfs_pageio_add_request(&pgio, new);
        nfs_pageio_complete(&pgio);
        return 0;
}

static void nfs_readpage_release(struct nfs_page *req)
{
        struct inode *d_inode = req->wb_context->dentry->d_inode;

        if (PageUptodate(req->wb_page))
                nfs_readpage_to_fscache(d_inode, req->wb_page, 0);

        unlock_page(req->wb_page);

        dprintk("NFS: read done (%s/%Ld %d@%Ld)\n",
                        req->wb_context->dentry->d_inode->i_sb->s_id,
                        (long long)NFS_FILEID(req->wb_context->dentry->d_inode),
                        req->wb_bytes,
                        (long long)req_offset(req));
        nfs_release_request(req);
}

int nfs_initiate_read(struct nfs_read_data *data, struct rpc_clnt *clnt,
                      const struct rpc_call_ops *call_ops)
{
        struct inode *inode = data->inode;
        int swap_flags = IS_SWAPFILE(inode) ? NFS_RPC_SWAPFLAGS : 0;
        struct rpc_task *task;
        struct rpc_message msg = {
                .rpc_argp = &data->args,
                .rpc_resp = &data->res,
                .rpc_cred = data->cred,
        };
        struct rpc_task_setup task_setup_data = {
                .task = &data->task,
                .rpc_client = clnt,
                .rpc_message = &msg,
                .callback_ops = call_ops,
                .callback_data = data,
                .workqueue = nfsiod_workqueue,
                .flags = RPC_TASK_ASYNC | swap_flags,
        };

        /* Set up the initial task struct. */
        NFS_PROTO(inode)->read_setup(data, &msg);

        dprintk("NFS: %5u initiated read call (req %s/%lld, %u bytes @ "
                        "offset %llu)\n",
                        data->task.tk_pid,
                        inode->i_sb->s_id,
                        (long long)NFS_FILEID(inode),
                        data->args.count,
                        (unsigned long long)data->args.offset);

        task = rpc_run_task(&task_setup_data);
        if (IS_ERR(task))
                return PTR_ERR(task);
        rpc_put_task(task);
        return 0;
}
EXPORT_SYMBOL_GPL(nfs_initiate_read);

/*
 * Set up the NFS read request struct
 */
static void nfs_read_rpcsetup(struct nfs_page *req, struct nfs_read_data *data,
                unsigned int count, unsigned int offset)
{
        struct inode *inode = req->wb_context->dentry->d_inode;

        data->req         = req;
        data->inode       = inode;
        data->cred        = req->wb_context->cred;

        data->args.fh     = NFS_FH(inode);
        data->args.offset = req_offset(req) + offset;
        data->args.pgbase = req->wb_pgbase + offset;
        data->args.pages  = data->pagevec;
        data->args.count  = count;
        data->args.context = get_nfs_open_context(req->wb_context);
        data->args.lock_context = req->wb_lock_context;

        data->res.fattr   = &data->fattr;
        data->res.count   = count;
        data->res.eof     = 0;
        nfs_fattr_init(&data->fattr);
}

static int nfs_do_read(struct nfs_read_data *data,
                const struct rpc_call_ops *call_ops)
{
        struct inode *inode = data->args.context->dentry->d_inode;

        return nfs_initiate_read(data, NFS_CLIENT(inode), call_ops);
}

static int
nfs_do_multiple_reads(struct list_head *head,
                const struct rpc_call_ops *call_ops)
{
        struct nfs_read_data *data;
        int ret = 0;

        while (!list_empty(head)) {
                int ret2;

                data = list_entry(head->next, struct nfs_read_data, list);
                list_del_init(&data->list);

                ret2 = nfs_do_read(data, call_ops);
                if (ret == 0)
                        ret = ret2;
        }
        return ret;
}

static void
nfs_async_read_error(struct list_head *head)
{
        struct nfs_page *req;

        while (!list_empty(head)) {
                req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_readpage_release(req);
        }
}

/*
 * Generate multiple requests to fill a single page.
 *
 * We optimize to reduce the number of read operations on the wire.  If we
 * detect that we're reading a page, or an area of a page, that is past the
 * end of file, we do not generate NFS read operations but just clear the
 * parts of the page that would have come back zero from the server anyway.
 *
 * We rely on the cached value of i_size to make this determination; another
 * client can fill pages on the server past our cached end-of-file, but we
 * won't see the new data until our attribute cache is updated.  This is more
 * or less conventional NFS client behavior.
 */
static int nfs_pagein_multi(struct nfs_pageio_descriptor *desc, struct list_head *res)
{
        struct nfs_page *req = nfs_list_entry(desc->pg_list.next);
        struct page *page = req->wb_page;
        struct nfs_read_data *data;
        size_t rsize = desc->pg_bsize, nbytes;
        unsigned int offset;
        int requests = 0;
        int ret = 0;

        nfs_list_remove_request(req);

        offset = 0;
        nbytes = desc->pg_count;
        do {
                size_t len = min(nbytes,rsize);

                data = nfs_readdata_alloc(1);
                if (!data)
                        goto out_bad;
                data->pagevec[0] = page;
                nfs_read_rpcsetup(req, data, len, offset);
                list_add(&data->list, res);
                requests++;
                nbytes -= len;
                offset += len;
        } while(nbytes != 0);
        atomic_set(&req->wb_complete, requests);
        desc->pg_rpc_callops = &nfs_read_partial_ops;
        return ret;
out_bad:
        while (!list_empty(res)) {
                data = list_entry(res->next, struct nfs_read_data, list);
                list_del(&data->list);
                nfs_readdata_free(data);
        }
        nfs_readpage_release(req);
        return -ENOMEM;
}

static int nfs_pagein_one(struct nfs_pageio_descriptor *desc, struct list_head *res)
{
        struct nfs_page         *req;
        struct page             **pages;
        struct nfs_read_data    *data;
        struct list_head *head = &desc->pg_list;
        int ret = 0;

        data = nfs_readdata_alloc(nfs_page_array_len(desc->pg_base,
                                                     desc->pg_count));
        if (!data) {
                nfs_async_read_error(head);
                ret = -ENOMEM;
                goto out;
        }

        pages = data->pagevec;
        while (!list_empty(head)) {
                req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_list_add_request(req, &data->pages);
                *pages++ = req->wb_page;
        }
        req = nfs_list_entry(data->pages.next);

        nfs_read_rpcsetup(req, data, desc->pg_count, 0);
        list_add(&data->list, res);
        desc->pg_rpc_callops = &nfs_read_full_ops;
out:
        return ret;
}

int nfs_generic_pagein(struct nfs_pageio_descriptor *desc, struct list_head *head)
{
        if (desc->pg_bsize < PAGE_CACHE_SIZE)
                return nfs_pagein_multi(desc, head);
        return nfs_pagein_one(desc, head);
}

static int nfs_generic_pg_readpages(struct nfs_pageio_descriptor *desc)
{
        LIST_HEAD(head);
        int ret;

        ret = nfs_generic_pagein(desc, &head);
        if (ret == 0)
                ret = nfs_do_multiple_reads(&head, desc->pg_rpc_callops);
        return ret;
}

static const struct nfs_pageio_ops nfs_pageio_read_ops = {
        .pg_test = nfs_generic_pg_test,
        .pg_doio = nfs_generic_pg_readpages,
};

/*
 * This is the callback from RPC telling us whether a reply was
 * received or some error occurred (timeout or socket shutdown).
 */
int nfs_readpage_result(struct rpc_task *task, struct nfs_read_data *data)
{
        int status;

        dprintk("NFS: %s: %5u, (status %d)\n", __func__, task->tk_pid,
                        task->tk_status);

        status = NFS_PROTO(data->inode)->read_done(task, data);
        if (status != 0)
                return status;

        nfs_add_stats(data->inode, NFSIOS_SERVERREADBYTES, data->res.count);

        if (task->tk_status == -ESTALE) {
                set_bit(NFS_INO_STALE, &NFS_I(data->inode)->flags);
                nfs_mark_for_revalidate(data->inode);
        }
        return 0;
}

static void nfs_readpage_retry(struct rpc_task *task, struct nfs_read_data *data)
{
        struct nfs_readargs *argp = &data->args;
        struct nfs_readres *resp = &data->res;

        if (resp->eof || resp->count == argp->count)
                return;

        /* This is a short read! */
        nfs_inc_stats(data->inode, NFSIOS_SHORTREAD);
        /* Has the server at least made some progress? */
        if (resp->count == 0)
                return;

        /* Yes, so retry the read at the end of the data */
        data->mds_offset += resp->count;
        argp->offset += resp->count;
        argp->pgbase += resp->count;
        argp->count -= resp->count;
        rpc_restart_call_prepare(task);
}

/*
 * Handle a read reply that fills part of a page.
 */
static void nfs_readpage_result_partial(struct rpc_task *task, void *calldata)
{
        struct nfs_read_data *data = calldata;
 
        if (nfs_readpage_result(task, data) != 0)
                return;
        if (task->tk_status < 0)
                return;

        nfs_readpage_truncate_uninitialised_page(data);
        nfs_readpage_retry(task, data);
}

static void nfs_readpage_release_partial(void *calldata)
{
        struct nfs_read_data *data = calldata;
        struct nfs_page *req = data->req;
        struct page *page = req->wb_page;
        int status = data->task.tk_status;

        if (status < 0)
                set_bit(PG_PARTIAL_READ_FAILED, &req->wb_flags);

        if (atomic_dec_and_test(&req->wb_complete)) {
                if (!test_bit(PG_PARTIAL_READ_FAILED, &req->wb_flags))
                        SetPageUptodate(page);
                nfs_readpage_release(req);
        }
        nfs_readdata_release(calldata);
}

#if defined(CONFIG_NFS_V4_1)
void nfs_read_prepare(struct rpc_task *task, void *calldata)
{
        struct nfs_read_data *data = calldata;

        if (nfs4_setup_sequence(NFS_SERVER(data->inode),
                                &data->args.seq_args, &data->res.seq_res,
                                0, task))
                return;
        rpc_call_start(task);
}
#endif /* CONFIG_NFS_V4_1 */

static const struct rpc_call_ops nfs_read_partial_ops = {
#if defined(CONFIG_NFS_V4_1)
        .rpc_call_prepare = nfs_read_prepare,
#endif /* CONFIG_NFS_V4_1 */
        .rpc_call_done = nfs_readpage_result_partial,
        .rpc_release = nfs_readpage_release_partial,
};

static void nfs_readpage_set_pages_uptodate(struct nfs_read_data *data)
{
        unsigned int count = data->res.count;
        unsigned int base = data->args.pgbase;
        struct page **pages;

        if (data->res.eof)
                count = data->args.count;
        if (unlikely(count == 0))
                return;
        pages = &data->args.pages[base >> PAGE_CACHE_SHIFT];
        base &= ~PAGE_CACHE_MASK;
        count += base;
        for (;count >= PAGE_CACHE_SIZE; count -= PAGE_CACHE_SIZE, pages++)
                SetPageUptodate(*pages);
        if (count == 0)
                return;
        /* Was this a short read? */
        if (data->res.eof || data->res.count == data->args.count)
                SetPageUptodate(*pages);
}

/*
 * This is the callback from RPC telling us whether a reply was
 * received or some error occurred (timeout or socket shutdown).
 */
static void nfs_readpage_result_full(struct rpc_task *task, void *calldata)
{
        struct nfs_read_data *data = calldata;

        if (nfs_readpage_result(task, data) != 0)
                return;
        if (task->tk_status < 0)
                return;
        /*
         * Note: nfs_readpage_retry may change the values of
         * data->args. In the multi-page case, we therefore need
         * to ensure that we call nfs_readpage_set_pages_uptodate()
         * first.
         */
        nfs_readpage_truncate_uninitialised_page(data);
        nfs_readpage_set_pages_uptodate(data);
        nfs_readpage_retry(task, data);
}

static void nfs_readpage_release_full(void *calldata)
{
        struct nfs_read_data *data = calldata;

        while (!list_empty(&data->pages)) {
                struct nfs_page *req = nfs_list_entry(data->pages.next);

                nfs_list_remove_request(req);
                nfs_readpage_release(req);
        }
        nfs_readdata_release(calldata);
}

static const struct rpc_call_ops nfs_read_full_ops = {
#if defined(CONFIG_NFS_V4_1)
        .rpc_call_prepare = nfs_read_prepare,
#endif /* CONFIG_NFS_V4_1 */
        .rpc_call_done = nfs_readpage_result_full,
        .rpc_release = nfs_readpage_release_full,
};

/*
 * Read a page over NFS.
 * We read the page synchronously in the following case:
 *  -   The error flag is set for this page. This happens only when a
 *      previous async read operation failed.
 */
int nfs_readpage(struct file *file, struct page *page)
{
        struct nfs_open_context *ctx;
        struct inode *inode = page->mapping->host;
        int             error;

        dprintk("NFS: nfs_readpage (%p %ld@%lu)\n",
                page, PAGE_CACHE_SIZE, page->index);
        nfs_inc_stats(inode, NFSIOS_VFSREADPAGE);
        nfs_add_stats(inode, NFSIOS_READPAGES, 1);

        /*
         * Try to flush any pending writes to the file..
         *
         * NOTE! Because we own the page lock, there cannot
         * be any new pending writes generated at this point
         * for this page (other pages can be written to).
         */
        error = nfs_wb_page(inode, page);
        if (error)
                goto out_unlock;
        if (PageUptodate(page))
                goto out_unlock;

        error = -ESTALE;
        if (NFS_STALE(inode))
                goto out_unlock;

        if (file == NULL) {
                error = -EBADF;
                ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
                if (ctx == NULL)
                        goto out_unlock;
        } else
                ctx = get_nfs_open_context(nfs_file_open_context(file));

        if (!IS_SYNC(inode)) {
                error = nfs_readpage_from_fscache(ctx, inode, page);
                if (error == 0)
                        goto out;
        }

        error = nfs_readpage_async(ctx, inode, page);

out:
        put_nfs_open_context(ctx);
        return error;
out_unlock:
        unlock_page(page);
        return error;
}

struct nfs_readdesc {
        struct nfs_pageio_descriptor *pgio;
        struct nfs_open_context *ctx;
};

static int
readpage_async_filler(void *data, struct page *page)
{
        struct nfs_readdesc *desc = (struct nfs_readdesc *)data;
        struct inode *inode = page->mapping->host;
        struct nfs_page *new;
        unsigned int len;
        int error;

        len = nfs_page_length(page);
        if (len == 0)
                return nfs_return_empty_page(page);

        new = nfs_create_request(desc->ctx, inode, page, 0, len);
        if (IS_ERR(new))
                goto out_error;

        if (len < PAGE_CACHE_SIZE)
                zero_user_segment(page, len, PAGE_CACHE_SIZE);
        if (!nfs_pageio_add_request(desc->pgio, new)) {
                error = desc->pgio->pg_error;
                goto out_unlock;
        }
        return 0;
out_error:
        error = PTR_ERR(new);
out_unlock:
        unlock_page(page);
        return error;
}

int nfs_readpages(struct file *filp, struct address_space *mapping,
                struct list_head *pages, unsigned nr_pages)
{
        struct nfs_pageio_descriptor pgio;
        struct nfs_readdesc desc = {
                .pgio = &pgio,
        };
        struct inode *inode = mapping->host;
        unsigned long npages;
        int ret = -ESTALE;

        dprintk("NFS: nfs_readpages (%s/%Ld %d)\n",
                        inode->i_sb->s_id,
                        (long long)NFS_FILEID(inode),
                        nr_pages);
        nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);

        if (NFS_STALE(inode))
                goto out;

        if (filp == NULL) {
                desc.ctx = nfs_find_open_context(inode, NULL, FMODE_READ);
                if (desc.ctx == NULL)
                        return -EBADF;
        } else
                desc.ctx = get_nfs_open_context(nfs_file_open_context(filp));

        /* attempt to read as many of the pages as possible from the cache
         * - this returns -ENOBUFS immediately if the cookie is negative
         */
        ret = nfs_readpages_from_fscache(desc.ctx, inode, mapping,
                                         pages, &nr_pages);
        if (ret == 0)
                goto read_complete; /* all pages were read */

        nfs_pageio_init_read(&pgio, inode);

        ret = read_cache_pages(mapping, pages, readpage_async_filler, &desc);

        nfs_pageio_complete(&pgio);
        npages = (pgio.pg_bytes_written + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
        nfs_add_stats(inode, NFSIOS_READPAGES, npages);
read_complete:
        put_nfs_open_context(desc.ctx);
out:
        return ret;
}

int __init nfs_init_readpagecache(void)
{
        nfs_rdata_cachep = kmem_cache_create("nfs_read_data",
                                             sizeof(struct nfs_read_data),
                                             0, SLAB_HWCACHE_ALIGN,
                                             NULL);
        if (nfs_rdata_cachep == NULL)
                return -ENOMEM;

        return 0;
}

void nfs_destroy_readpagecache(void)
{
        kmem_cache_destroy(nfs_rdata_cachep);
}