diff options
| -rw-r--r-- | Documentation/filesystems/Locking | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.txt | 14 | ||||
| -rw-r--r-- | fs/dcache.c | 5 | ||||
| -rw-r--r-- | fs/namei.c | 226 | ||||
| -rw-r--r-- | include/linux/dcache.h | 7 | ||||
| -rw-r--r-- | include/linux/fs.h | 2 |
6 files changed, 198 insertions, 58 deletions
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index 977d8919cc69..5f0c52a07386 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -19,6 +19,7 @@ prototypes: void (*d_release)(struct dentry *); void (*d_iput)(struct dentry *, struct inode *); char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen); + struct vfsmount *(*d_automount)(struct path *path); locking rules: rename_lock ->d_lock may block rcu-walk @@ -29,6 +30,7 @@ d_delete: no yes no no d_release: no no yes no d_iput: no no yes no d_dname: no no no no +d_automount: no no yes no --------------------------- inode_operations --------------------------- prototypes: diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index cae6d27c9f5b..726a4f6fa3c9 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -864,6 +864,7 @@ struct dentry_operations { void (*d_release)(struct dentry *); void (*d_iput)(struct dentry *, struct inode *); char *(*d_dname)(struct dentry *, char *, int); + struct vfsmount *(*d_automount)(struct path *); }; d_revalidate: called when the VFS needs to revalidate a dentry. This @@ -930,6 +931,19 @@ struct dentry_operations { at the end of the buffer, and returns a pointer to the first char. dynamic_dname() helper function is provided to take care of this. + d_automount: called when an automount dentry is to be traversed (optional). + This should create a new VFS mount record, mount it on the directory + and return the record to the caller. The caller is supplied with a + path parameter giving the automount directory to describe the automount + target and the parent VFS mount record to provide inheritable mount + parameters. NULL should be returned if someone else managed to make + the automount first. If the automount failed, then an error code + should be returned. + + This function is only used if DCACHE_NEED_AUTOMOUNT is set on the + dentry. This is set by __d_instantiate() if S_AUTOMOUNT is set on the + inode being added. + Example : static char *pipefs_dname(struct dentry *dent, char *buffer, int buflen) diff --git a/fs/dcache.c b/fs/dcache.c index 0c6d5c549d84..51f7bb6463af 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1380,8 +1380,11 @@ EXPORT_SYMBOL(d_set_d_op); static void __d_instantiate(struct dentry *dentry, struct inode *inode) { spin_lock(&dentry->d_lock); - if (inode) + if (inode) { + if (unlikely(IS_AUTOMOUNT(inode))) + dentry->d_flags |= DCACHE_NEED_AUTOMOUNT; list_add(&dentry->d_alias, &inode->i_dentry); + } dentry->d_inode = inode; dentry_rcuwalk_barrier(dentry); spin_unlock(&dentry->d_lock); diff --git a/fs/namei.c b/fs/namei.c index 529e917ad2fc..16109da68bbf 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -896,51 +896,120 @@ int follow_up(struct path *path) } /* - * serialization is taken care of in namespace.c + * Perform an automount + * - return -EISDIR to tell follow_managed() to stop and return the path we + * were called with. */ -static void __follow_mount_rcu(struct nameidata *nd, struct path *path, - struct inode **inode) +static int follow_automount(struct path *path, unsigned flags, + bool *need_mntput) { - while (d_mountpoint(path->dentry)) { - struct vfsmount *mounted; - mounted = __lookup_mnt(path->mnt, path->dentry, 1); - if (!mounted) - return; - path->mnt = mounted; - path->dentry = mounted->mnt_root; - nd->seq = read_seqcount_begin(&path->dentry->d_seq); - *inode = path->dentry->d_inode; + struct vfsmount *mnt; + + if (!path->dentry->d_op || !path->dentry->d_op->d_automount) + return -EREMOTE; + + /* We want to mount if someone is trying to open/create a file of any + * type under the mountpoint, wants to traverse through the mountpoint + * or wants to open the mounted directory. + * + * We don't want to mount if someone's just doing a stat and they've + * set AT_SYMLINK_NOFOLLOW - unless they're stat'ing a directory and + * appended a '/' to the name. + */ + if (!(flags & LOOKUP_FOLLOW) && + !(flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY | + LOOKUP_OPEN | LOOKUP_CREATE))) + return -EISDIR; + + current->total_link_count++; + if (current->total_link_count >= 40) + return -ELOOP; + + mnt = path->dentry->d_op->d_automount(path); + if (IS_ERR(mnt)) { + /* + * The filesystem is allowed to return -EISDIR here to indicate + * it doesn't want to automount. For instance, autofs would do + * this so that its userspace daemon can mount on this dentry. + * + * However, we can only permit this if it's a terminal point in + * the path being looked up; if it wasn't then the remainder of + * the path is inaccessible and we should say so. + */ + if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_CONTINUE)) + return -EREMOTE; + return PTR_ERR(mnt); } -} + if (!mnt) /* mount collision */ + return 0; -static int __follow_mount(struct path *path) -{ - int res = 0; - while (d_mountpoint(path->dentry)) { - struct vfsmount *mounted = lookup_mnt(path); - if (!mounted) - break; - dput(path->dentry); - if (res) - mntput(path->mnt); - path->mnt = mounted; - path->dentry = dget(mounted->mnt_root); - res = 1; + if (mnt->mnt_sb == path->mnt->mnt_sb && + mnt->mnt_root == path->dentry) { + mntput(mnt); + return -ELOOP; } - return res; + + dput(path->dentry); + if (*need_mntput) + mntput(path->mnt); + path->mnt = mnt; + path->dentry = dget(mnt->mnt_root); + *need_mntput = true; + return 0; } -static void follow_mount(struct path *path) +/* + * Handle a dentry that is managed in some way. + * - Flagged as mountpoint + * - Flagged as automount point + * + * This may only be called in refwalk mode. + * + * Serialization is taken care of in namespace.c + */ +static int follow_managed(struct path *path, unsigned flags) { - while (d_mountpoint(path->dentry)) { - struct vfsmount *mounted = lookup_mnt(path); - if (!mounted) - break; - dput(path->dentry); - mntput(path->mnt); - path->mnt = mounted; - path->dentry = dget(mounted->mnt_root); + unsigned managed; + bool need_mntput = false; + int ret; + + /* Given that we're not holding a lock here, we retain the value in a + * local variable for each dentry as we look at it so that we don't see + * the components of that value change under us */ + while (managed = ACCESS_ONCE(path->dentry->d_flags), + managed &= DCACHE_MANAGED_DENTRY, + unlikely(managed != 0)) { + /* Transit to a mounted filesystem. */ + if (managed & DCACHE_MOUNTED) { + struct vfsmount *mounted = lookup_mnt(path); + if (mounted) { + dput(path->dentry); + if (need_mntput) + mntput(path->mnt); + path->mnt = mounted; + path->dentry = dget(mounted->mnt_root); + need_mntput = true; + continue; + } + + /* Something is mounted on this dentry in another + * namespace and/or whatever was mounted there in this + * namespace got unmounted before we managed to get the + * vfsmount_lock */ + } + + /* Handle an automount point */ + if (managed & DCACHE_NEED_AUTOMOUNT) { + ret = follow_automount(path, flags, &need_mntput); + if (ret < 0) + return ret == -EISDIR ? 0 : ret; + continue; + } + + /* We didn't change the current path point */ + break; } + return 0; } int follow_down(struct path *path) @@ -958,13 +1027,37 @@ int follow_down(struct path *path) return 0; } +/* + * Skip to top of mountpoint pile in rcuwalk mode. We abort the rcu-walk if we + * meet an automount point and we're not walking to "..". True is returned to + * continue, false to abort. + */ +static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, + struct inode **inode, bool reverse_transit) +{ + while (d_mountpoint(path->dentry)) { + struct vfsmount *mounted; + mounted = __lookup_mnt(path->mnt, path->dentry, 1); + if (!mounted) + break; + path->mnt = mounted; + path->dentry = mounted->mnt_root; + nd->seq = read_seqcount_begin(&path->dentry->d_seq); + *inode = path->dentry->d_inode; + } + + if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT)) + return reverse_transit; + return true; +} + static int follow_dotdot_rcu(struct nameidata *nd) { struct inode *inode = nd->inode; set_root_rcu(nd); - while(1) { + while (1) { if (nd->path.dentry == nd->root.dentry && nd->path.mnt == nd->root.mnt) { break; @@ -987,12 +1080,28 @@ static int follow_dotdot_rcu(struct nameidata *nd) nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); inode = nd->path.dentry->d_inode; } - __follow_mount_rcu(nd, &nd->path, &inode); + __follow_mount_rcu(nd, &nd->path, &inode, true); nd->inode = inode; return 0; } +/* + * Skip to top of mountpoint pile in refwalk mode for follow_dotdot() + */ +static void follow_mount(struct path *path) +{ + while (d_mountpoint(path->dentry)) { + struct vfsmount *mounted = lookup_mnt(path); + if (!mounted) + break; + dput(path->dentry); + mntput(path->mnt); + path->mnt = mounted; + path->dentry = dget(mounted->mnt_root); + } +} + static void follow_dotdot(struct nameidata *nd) { set_root(nd); @@ -1057,12 +1166,14 @@ static int do_lookup(struct nameidata *nd, struct qstr *name, struct vfsmount *mnt = nd->path.mnt; struct dentry *dentry, *parent = nd->path.dentry; struct inode *dir; + int err; + /* * See if the low-level filesystem might want * to use its own hash.. */ if (unlikely(parent->d_flags & DCACHE_OP_HASH)) { - int err = parent->d_op->d_hash(parent, nd->inode, name); + err = parent->d_op->d_hash(parent, nd->inode, name); if (err < 0) return err; } @@ -1092,20 +1203,25 @@ static int do_lookup(struct nameidata *nd, struct qstr *name, done2: path->mnt = mnt; path->dentry = dentry; - __follow_mount_rcu(nd, path, inode); - } else { - dentry = __d_lookup(parent, name); - if (!dentry) - goto need_lookup; + if (likely(__follow_mount_rcu(nd, path, inode, false))) + return 0; + if (nameidata_drop_rcu(nd)) + return -ECHILD; + /* fallthru */ + } + dentry = __d_lookup(parent, name); + if (!dentry) + goto need_lookup; found: - if (dentry->d_flags & DCACHE_OP_REVALIDATE) - goto need_revalidate; + if (dentry->d_flags & DCACHE_OP_REVALIDATE) + goto need_revalidate; done: - path->mnt = mnt; - path->dentry = dentry; - __follow_mount(path); - *inode = path->dentry->d_inode; - } + path->mnt = mnt; + path->dentry = dentry; + err = follow_managed(path, nd->flags); + if (unlikely(err < 0)) + return err; + *inode = path->dentry->d_inode; return 0; need_lookup: @@ -2203,11 +2319,9 @@ static struct file *do_last(struct nameidata *nd, struct path *path, if (open_flag & O_EXCL) goto exit_dput; - if (__follow_mount(path)) { - error = -ELOOP; - if (open_flag & O_NOFOLLOW) - goto exit_dput; - } + error = follow_managed(path, nd->flags); + if (error < 0) + goto exit_dput; error = -ENOENT; if (!path->dentry->d_inode) diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 59fcd24b1468..ee6c26d142c3 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -167,6 +167,7 @@ struct dentry_operations { void (*d_release)(struct dentry *); void (*d_iput)(struct dentry *, struct inode *); char *(*d_dname)(struct dentry *, char *, int); + struct vfsmount *(*d_automount)(struct path *); } ____cacheline_aligned; /* @@ -205,13 +206,17 @@ struct dentry_operations { #define DCACHE_CANT_MOUNT 0x0100 #define DCACHE_GENOCIDE 0x0200 -#define DCACHE_MOUNTED 0x0400 /* is a mountpoint */ #define DCACHE_OP_HASH 0x1000 #define DCACHE_OP_COMPARE 0x2000 #define DCACHE_OP_REVALIDATE 0x4000 #define DCACHE_OP_DELETE 0x8000 +#define DCACHE_MOUNTED 0x10000 /* is a mountpoint */ +#define DCACHE_NEED_AUTOMOUNT 0x20000 /* handle automount on this dir */ +#define DCACHE_MANAGED_DENTRY \ + (DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT) + extern seqlock_t rename_lock; static inline int dname_external(struct dentry *dentry) diff --git a/include/linux/fs.h b/include/linux/fs.h index 3984f2358d1f..4c00ed53be8f 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -242,6 +242,7 @@ struct inodes_stat_t { #define S_SWAPFILE 256 /* Do not truncate: swapon got its bmaps */ #define S_PRIVATE 512 /* Inode is fs-internal */ #define S_IMA 1024 /* Inode has an associated IMA struct */ +#define S_AUTOMOUNT 2048 /* Automount/referral quasi-directory */ /* * Note that nosuid etc flags are inode-specific: setting some file-system @@ -277,6 +278,7 @@ struct inodes_stat_t { #define IS_SWAPFILE(inode) ((inode)->i_flags & S_SWAPFILE) #define IS_PRIVATE(inode) ((inode)->i_flags & S_PRIVATE) #define IS_IMA(inode) ((inode)->i_flags & S_IMA) +#define IS_AUTOMOUNT(inode) ((inode)->i_flags & S_AUTOMOUNT) /* the read-only stuff doesn't really belong here, but any other place is probably as bad and I don't want to create yet another include file. */ |