linux/fs/9p/fid.c
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   1/*
   2 * V9FS FID Management
   3 *
   4 *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
   5 *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
   6 *
   7 *  This program is free software; you can redistribute it and/or modify
   8 *  it under the terms of the GNU General Public License version 2
   9 *  as published by the Free Software Foundation.
  10 *
  11 *  This program is distributed in the hope that it will be useful,
  12 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 *  GNU General Public License for more details.
  15 *
  16 *  You should have received a copy of the GNU General Public License
  17 *  along with this program; if not, write to:
  18 *  Free Software Foundation
  19 *  51 Franklin Street, Fifth Floor
  20 *  Boston, MA  02111-1301  USA
  21 *
  22 */
  23
  24#include <linux/module.h>
  25#include <linux/errno.h>
  26#include <linux/fs.h>
  27#include <linux/slab.h>
  28#include <linux/sched.h>
  29#include <linux/idr.h>
  30#include <net/9p/9p.h>
  31#include <net/9p/client.h>
  32
  33#include "v9fs.h"
  34#include "v9fs_vfs.h"
  35#include "fid.h"
  36
  37/**
  38 * v9fs_fid_add - add a fid to a dentry
  39 * @dentry: dentry that the fid is being added to
  40 * @fid: fid to add
  41 *
  42 */
  43
  44static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
  45{
  46        hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
  47}
  48
  49void v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
  50{
  51        spin_lock(&dentry->d_lock);
  52        __add_fid(dentry, fid);
  53        spin_unlock(&dentry->d_lock);
  54}
  55
  56/**
  57 * v9fs_fid_find - retrieve a fid that belongs to the specified uid
  58 * @dentry: dentry to look for fid in
  59 * @uid: return fid that belongs to the specified user
  60 * @any: if non-zero, return any fid associated with the dentry
  61 *
  62 */
  63
  64static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
  65{
  66        struct p9_fid *fid, *ret;
  67
  68        p9_debug(P9_DEBUG_VFS, " dentry: %s (%p) uid %d any %d\n",
  69                 dentry->d_name.name, dentry, from_kuid(&init_user_ns, uid),
  70                 any);
  71        ret = NULL;
  72        /* we'll recheck under lock if there's anything to look in */
  73        if (dentry->d_fsdata) {
  74                struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
  75                spin_lock(&dentry->d_lock);
  76                hlist_for_each_entry(fid, h, dlist) {
  77                        if (any || uid_eq(fid->uid, uid)) {
  78                                ret = fid;
  79                                break;
  80                        }
  81                }
  82                spin_unlock(&dentry->d_lock);
  83        }
  84
  85        return ret;
  86}
  87
  88/*
  89 * We need to hold v9ses->rename_sem as long as we hold references
  90 * to returned path array. Array element contain pointers to
  91 * dentry names.
  92 */
  93static int build_path_from_dentry(struct v9fs_session_info *v9ses,
  94                                  struct dentry *dentry, char ***names)
  95{
  96        int n = 0, i;
  97        char **wnames;
  98        struct dentry *ds;
  99
 100        for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
 101                n++;
 102
 103        wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
 104        if (!wnames)
 105                goto err_out;
 106
 107        for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
 108                wnames[i] = (char  *)ds->d_name.name;
 109
 110        *names = wnames;
 111        return n;
 112err_out:
 113        return -ENOMEM;
 114}
 115
 116static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 117                                               kuid_t uid, int any)
 118{
 119        struct dentry *ds;
 120        char **wnames, *uname;
 121        int i, n, l, clone, access;
 122        struct v9fs_session_info *v9ses;
 123        struct p9_fid *fid, *old_fid = NULL;
 124
 125        v9ses = v9fs_dentry2v9ses(dentry);
 126        access = v9ses->flags & V9FS_ACCESS_MASK;
 127        fid = v9fs_fid_find(dentry, uid, any);
 128        if (fid)
 129                return fid;
 130        /*
 131         * we don't have a matching fid. To do a TWALK we need
 132         * parent fid. We need to prevent rename when we want to
 133         * look at the parent.
 134         */
 135        down_read(&v9ses->rename_sem);
 136        ds = dentry->d_parent;
 137        fid = v9fs_fid_find(ds, uid, any);
 138        if (fid) {
 139                /* Found the parent fid do a lookup with that */
 140                fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
 141                goto fid_out;
 142        }
 143        up_read(&v9ses->rename_sem);
 144
 145        /* start from the root and try to do a lookup */
 146        fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
 147        if (!fid) {
 148                /* the user is not attached to the fs yet */
 149                if (access == V9FS_ACCESS_SINGLE)
 150                        return ERR_PTR(-EPERM);
 151
 152                if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
 153                                uname = NULL;
 154                else
 155                        uname = v9ses->uname;
 156
 157                fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
 158                                       v9ses->aname);
 159                if (IS_ERR(fid))
 160                        return fid;
 161
 162                v9fs_fid_add(dentry->d_sb->s_root, fid);
 163        }
 164        /* If we are root ourself just return that */
 165        if (dentry->d_sb->s_root == dentry)
 166                return fid;
 167        /*
 168         * Do a multipath walk with attached root.
 169         * When walking parent we need to make sure we
 170         * don't have a parallel rename happening
 171         */
 172        down_read(&v9ses->rename_sem);
 173        n  = build_path_from_dentry(v9ses, dentry, &wnames);
 174        if (n < 0) {
 175                fid = ERR_PTR(n);
 176                goto err_out;
 177        }
 178        clone = 1;
 179        i = 0;
 180        while (i < n) {
 181                l = min(n - i, P9_MAXWELEM);
 182                /*
 183                 * We need to hold rename lock when doing a multipath
 184                 * walk to ensure none of the patch component change
 185                 */
 186                fid = p9_client_walk(fid, l, &wnames[i], clone);
 187                if (IS_ERR(fid)) {
 188                        if (old_fid) {
 189                                /*
 190                                 * If we fail, clunk fid which are mapping
 191                                 * to path component and not the last component
 192                                 * of the path.
 193                                 */
 194                                p9_client_clunk(old_fid);
 195                        }
 196                        kfree(wnames);
 197                        goto err_out;
 198                }
 199                old_fid = fid;
 200                i += l;
 201                clone = 0;
 202        }
 203        kfree(wnames);
 204fid_out:
 205        if (!IS_ERR(fid)) {
 206                spin_lock(&dentry->d_lock);
 207                if (d_unhashed(dentry)) {
 208                        spin_unlock(&dentry->d_lock);
 209                        p9_client_clunk(fid);
 210                        fid = ERR_PTR(-ENOENT);
 211                } else {
 212                        __add_fid(dentry, fid);
 213                        spin_unlock(&dentry->d_lock);
 214                }
 215        }
 216err_out:
 217        up_read(&v9ses->rename_sem);
 218        return fid;
 219}
 220
 221/**
 222 * v9fs_fid_lookup - lookup for a fid, try to walk if not found
 223 * @dentry: dentry to look for fid in
 224 *
 225 * Look for a fid in the specified dentry for the current user.
 226 * If no fid is found, try to create one walking from a fid from the parent
 227 * dentry (if it has one), or the root dentry. If the user haven't accessed
 228 * the fs yet, attach now and walk from the root.
 229 */
 230
 231struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
 232{
 233        kuid_t uid;
 234        int  any, access;
 235        struct v9fs_session_info *v9ses;
 236
 237        v9ses = v9fs_dentry2v9ses(dentry);
 238        access = v9ses->flags & V9FS_ACCESS_MASK;
 239        switch (access) {
 240        case V9FS_ACCESS_SINGLE:
 241        case V9FS_ACCESS_USER:
 242        case V9FS_ACCESS_CLIENT:
 243                uid = current_fsuid();
 244                any = 0;
 245                break;
 246
 247        case V9FS_ACCESS_ANY:
 248                uid = v9ses->uid;
 249                any = 1;
 250                break;
 251
 252        default:
 253                uid = INVALID_UID;
 254                any = 0;
 255                break;
 256        }
 257        return v9fs_fid_lookup_with_uid(dentry, uid, any);
 258}
 259
 260struct p9_fid *v9fs_fid_clone(struct dentry *dentry)
 261{
 262        struct p9_fid *fid, *ret;
 263
 264        fid = v9fs_fid_lookup(dentry);
 265        if (IS_ERR(fid))
 266                return fid;
 267
 268        ret = p9_client_walk(fid, 0, NULL, 1);
 269        return ret;
 270}
 271
 272static struct p9_fid *v9fs_fid_clone_with_uid(struct dentry *dentry, kuid_t uid)
 273{
 274        struct p9_fid *fid, *ret;
 275
 276        fid = v9fs_fid_lookup_with_uid(dentry, uid, 0);
 277        if (IS_ERR(fid))
 278                return fid;
 279
 280        ret = p9_client_walk(fid, 0, NULL, 1);
 281        return ret;
 282}
 283
 284struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
 285{
 286        int err;
 287        struct p9_fid *fid;
 288
 289        fid = v9fs_fid_clone_with_uid(dentry, GLOBAL_ROOT_UID);
 290        if (IS_ERR(fid))
 291                goto error_out;
 292        /*
 293         * writeback fid will only be used to write back the
 294         * dirty pages. We always request for the open fid in read-write
 295         * mode so that a partial page write which result in page
 296         * read can work.
 297         */
 298        err = p9_client_open(fid, O_RDWR);
 299        if (err < 0) {
 300                p9_client_clunk(fid);
 301                fid = ERR_PTR(err);
 302                goto error_out;
 303        }
 304error_out:
 305        return fid;
 306}
 307
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