fs/9p/fid.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * V9FS FID Management
0004  *
0005  *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
0006  *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
0007  */
0008
0009 #include <linux/module.h>
0010 #include <linux/errno.h>
0011 #include <linux/fs.h>
0012 #include <linux/slab.h>
0013 #include <linux/sched.h>
0014 #include <linux/idr.h>
0015 #include <net/9p/9p.h>
0016 #include <net/9p/client.h>
0017
0018 #include "v9fs.h"
0019 #include "v9fs_vfs.h"
0020 #include "fid.h"
0021
0022 static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
0023 {
0024     hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
0025 }
0026
0027
0028 /**
0029  * v9fs_fid_add - add a fid to a dentry
0030  * @dentry: dentry that the fid is being added to
0031  * @pfid: fid to add, NULLed out
0032  *
0033  */
0034 void v9fs_fid_add(struct dentry *dentry, struct p9_fid **pfid)
0035 {
0036     struct p9_fid *fid = *pfid;
0037
0038     spin_lock(&dentry->d_lock);
0039     __add_fid(dentry, fid);
0040     spin_unlock(&dentry->d_lock);
0041
0042     *pfid = NULL;
0043 }
0044
0045 /**
0046  * v9fs_fid_find_inode - search for an open fid off of the inode list
0047  * @inode: return a fid pointing to a specific inode
0048  * @uid: return a fid belonging to the specified user
0049  *
0050  */
0051
0052 static struct p9_fid *v9fs_fid_find_inode(struct inode *inode, kuid_t uid)
0053 {
0054     struct hlist_head *h;
0055     struct p9_fid *fid, *ret = NULL;
0056
0057     p9_debug(P9_DEBUG_VFS, " inode: %p\n", inode);
0058
0059     spin_lock(&inode->i_lock);
0060     h = (struct hlist_head *)&inode->i_private;
0061     hlist_for_each_entry(fid, h, ilist) {
0062         if (uid_eq(fid->uid, uid)) {
0063             p9_fid_get(fid);
0064             ret = fid;
0065             break;
0066         }
0067     }
0068     spin_unlock(&inode->i_lock);
0069     return ret;
0070 }
0071
0072 /**
0073  * v9fs_open_fid_add - add an open fid to an inode
0074  * @inode: inode that the fid is being added to
0075  * @pfid: fid to add, NULLed out
0076  *
0077  */
0078
0079 void v9fs_open_fid_add(struct inode *inode, struct p9_fid **pfid)
0080 {
0081     struct p9_fid *fid = *pfid;
0082
0083     spin_lock(&inode->i_lock);
0084     hlist_add_head(&fid->ilist, (struct hlist_head *)&inode->i_private);
0085     spin_unlock(&inode->i_lock);
0086
0087     *pfid = NULL;
0088 }
0089
0090
0091 /**
0092  * v9fs_fid_find - retrieve a fid that belongs to the specified uid
0093  * @dentry: dentry to look for fid in
0094  * @uid: return fid that belongs to the specified user
0095  * @any: if non-zero, return any fid associated with the dentry
0096  *
0097  */
0098
0099 static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
0100 {
0101     struct p9_fid *fid, *ret;
0102
0103     p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p) uid %d any %d\n",
0104          dentry, dentry, from_kuid(&init_user_ns, uid),
0105          any);
0106     ret = NULL;
0107     /* we'll recheck under lock if there's anything to look in */
0108     if (dentry->d_fsdata) {
0109         struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
0110
0111         spin_lock(&dentry->d_lock);
0112         hlist_for_each_entry(fid, h, dlist) {
0113             if (any || uid_eq(fid->uid, uid)) {
0114                 ret = fid;
0115                 p9_fid_get(ret);
0116                 break;
0117             }
0118         }
0119         spin_unlock(&dentry->d_lock);
0120     } else {
0121         if (dentry->d_inode)
0122             ret = v9fs_fid_find_inode(dentry->d_inode, uid);
0123     }
0124
0125     return ret;
0126 }
0127
0128 /*
0129  * We need to hold v9ses->rename_sem as long as we hold references
0130  * to returned path array. Array element contain pointers to
0131  * dentry names.
0132  */
0133 static int build_path_from_dentry(struct v9fs_session_info *v9ses,
0134                   struct dentry *dentry, const unsigned char ***names)
0135 {
0136     int n = 0, i;
0137     const unsigned char **wnames;
0138     struct dentry *ds;
0139
0140     for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
0141         n++;
0142
0143     wnames = kmalloc_array(n, sizeof(char *), GFP_KERNEL);
0144     if (!wnames)
0145         goto err_out;
0146
0147     for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
0148         wnames[i] = ds->d_name.name;
0149
0150     *names = wnames;
0151     return n;
0152 err_out:
0153     return -ENOMEM;
0154 }
0155
0156 static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
0157                            kuid_t uid, int any)
0158 {
0159     struct dentry *ds;
0160     const unsigned char **wnames, *uname;
0161     int i, n, l, access;
0162     struct v9fs_session_info *v9ses;
0163     struct p9_fid *fid, *root_fid, *old_fid;
0164
0165     v9ses = v9fs_dentry2v9ses(dentry);
0166     access = v9ses->flags & V9FS_ACCESS_MASK;
0167     fid = v9fs_fid_find(dentry, uid, any);
0168     if (fid)
0169         return fid;
0170     /*
0171      * we don't have a matching fid. To do a TWALK we need
0172      * parent fid. We need to prevent rename when we want to
0173      * look at the parent.
0174      */
0175     down_read(&v9ses->rename_sem);
0176     ds = dentry->d_parent;
0177     fid = v9fs_fid_find(ds, uid, any);
0178     if (fid) {
0179         /* Found the parent fid do a lookup with that */
0180         old_fid = fid;
0181
0182         fid = p9_client_walk(old_fid, 1, &dentry->d_name.name, 1);
0183         p9_fid_put(old_fid);
0184         goto fid_out;
0185     }
0186     up_read(&v9ses->rename_sem);
0187
0188     /* start from the root and try to do a lookup */
0189     root_fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
0190     if (!root_fid) {
0191         /* the user is not attached to the fs yet */
0192         if (access == V9FS_ACCESS_SINGLE)
0193             return ERR_PTR(-EPERM);
0194
0195         if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
0196             uname = NULL;
0197         else
0198             uname = v9ses->uname;
0199
0200         fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
0201                        v9ses->aname);
0202         if (IS_ERR(fid))
0203             return fid;
0204
0205         root_fid = p9_fid_get(fid);
0206         v9fs_fid_add(dentry->d_sb->s_root, &fid);
0207     }
0208     /* If we are root ourself just return that */
0209     if (dentry->d_sb->s_root == dentry)
0210         return root_fid;
0211
0212     /*
0213      * Do a multipath walk with attached root.
0214      * When walking parent we need to make sure we
0215      * don't have a parallel rename happening
0216      */
0217     down_read(&v9ses->rename_sem);
0218     n  = build_path_from_dentry(v9ses, dentry, &wnames);
0219     if (n < 0) {
0220         fid = ERR_PTR(n);
0221         goto err_out;
0222     }
0223     fid = root_fid;
0224     old_fid = root_fid;
0225     i = 0;
0226     while (i < n) {
0227         l = min(n - i, P9_MAXWELEM);
0228         /*
0229          * We need to hold rename lock when doing a multipath
0230          * walk to ensure none of the path components change
0231          */
0232         fid = p9_client_walk(old_fid, l, &wnames[i],
0233                      old_fid == root_fid /* clone */);
0234         /* non-cloning walk will return the same fid */
0235         if (fid != old_fid) {
0236             p9_fid_put(old_fid);
0237             old_fid = fid;
0238         }
0239         if (IS_ERR(fid)) {
0240             kfree(wnames);
0241             goto err_out;
0242         }
0243         i += l;
0244     }
0245     kfree(wnames);
0246 fid_out:
0247     if (!IS_ERR(fid)) {
0248         spin_lock(&dentry->d_lock);
0249         if (d_unhashed(dentry)) {
0250             spin_unlock(&dentry->d_lock);
0251             p9_fid_put(fid);
0252             fid = ERR_PTR(-ENOENT);
0253         } else {
0254             __add_fid(dentry, fid);
0255             p9_fid_get(fid);
0256             spin_unlock(&dentry->d_lock);
0257         }
0258     }
0259 err_out:
0260     up_read(&v9ses->rename_sem);
0261     return fid;
0262 }
0263
0264 /**
0265  * v9fs_fid_lookup - lookup for a fid, try to walk if not found
0266  * @dentry: dentry to look for fid in
0267  *
0268  * Look for a fid in the specified dentry for the current user.
0269  * If no fid is found, try to create one walking from a fid from the parent
0270  * dentry (if it has one), or the root dentry. If the user haven't accessed
0271  * the fs yet, attach now and walk from the root.
0272  */
0273
0274 struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
0275 {
0276     kuid_t uid;
0277     int  any, access;
0278     struct v9fs_session_info *v9ses;
0279
0280     v9ses = v9fs_dentry2v9ses(dentry);
0281     access = v9ses->flags & V9FS_ACCESS_MASK;
0282     switch (access) {
0283     case V9FS_ACCESS_SINGLE:
0284     case V9FS_ACCESS_USER:
0285     case V9FS_ACCESS_CLIENT:
0286         uid = current_fsuid();
0287         any = 0;
0288         break;
0289
0290     case V9FS_ACCESS_ANY:
0291         uid = v9ses->uid;
0292         any = 1;
0293         break;
0294
0295     default:
0296         uid = INVALID_UID;
0297         any = 0;
0298         break;
0299     }
0300     return v9fs_fid_lookup_with_uid(dentry, uid, any);
0301 }
0302
0303 struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
0304 {
0305     int err;
0306     struct p9_fid *fid, *ofid;
0307
0308     ofid = v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0);
0309     fid = clone_fid(ofid);
0310     if (IS_ERR(fid))
0311         goto error_out;
0312     p9_fid_put(ofid);
0313     /*
0314      * writeback fid will only be used to write back the
0315      * dirty pages. We always request for the open fid in read-write
0316      * mode so that a partial page write which result in page
0317      * read can work.
0318      */
0319     err = p9_client_open(fid, O_RDWR);
0320     if (err < 0) {
0321         p9_fid_put(fid);
0322         fid = ERR_PTR(err);
0323         goto error_out;
0324     }
0325 error_out:
0326     return fid;
0327 }