Add a dentry op (d_automount) to handle automounting directories rather than abusing the follow_link() inode operation. The operation is keyed off a new inode flag (S_AUTOMOUNT). This makes it easier to add an AT_ flag to suppress terminal segment automount during pathwalk. It should also remove the need for the kludge code in the pathwalk algorithm to handle directories with follow_link() semantics. I've only changed __follow_mount() to handle automount points, but it might be necessary to change follow_mount() too. The latter is only used from follow_dotdot(), but any automounts on ".." should be pinned whilst we're using a child of it. Note that autofs4's use of follow_mount() will need examining if this patch is committed. Signed-off-by: David Howells <dhowells@xxxxxxxxxx> --- Documentation/filesystems/Locking | 2 + Documentation/filesystems/vfs.txt | 13 ++++++ fs/namei.c | 85 +++++++++++++++++++++++++++++-------- fs/stat.c | 2 + include/linux/dcache.h | 5 ++ include/linux/fs.h | 2 + 6 files changed, 91 insertions(+), 18 deletions(-) diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index 96d4293..ccbfa98 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -16,6 +16,7 @@ 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: none have BKL @@ -27,6 +28,7 @@ d_delete: yes no yes no d_release: no no no yes d_iput: no no no yes d_dname: no no no no +d_automount: no no no yes --------------------------- inode_operations --------------------------- prototypes: diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 94677e7..31a9e8f 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -851,6 +851,7 @@ 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 @@ -885,6 +886,18 @@ 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 S_AUTOMOUNT is set on the inode to which + the dentry refers. + Example : static char *pipefs_dname(struct dentry *dent, char *buffer, int buflen) diff --git a/fs/namei.c b/fs/namei.c index 868d0cb..fcec3c6 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -617,24 +617,71 @@ int follow_up(struct path *path) return 1; } +/* + * Perform an automount + */ +static int follow_automount(struct path *path, int res) +{ + struct vfsmount *mnt; + + if (!path->dentry->d_op || !path->dentry->d_op->d_automount) + return -EREMOTE; + + current->total_link_count++; + if (current->total_link_count >= 40) + return -ELOOP; + + mnt = path->dentry->d_op->d_automount(path); + if (IS_ERR(mnt)) + return PTR_ERR(mnt); + if (!mnt) /* mount collision */ + return 0; + + if (mnt->mnt_sb == path->mnt->mnt_sb && + mnt->mnt_root == path->dentry) { + mntput(mnt); + return -ELOOP; + } + + dput(path->dentry); + if (res) + mntput(path->mnt); + path->mnt = mnt; + path->dentry = dget(mnt->mnt_root); + return 0; +} + /* no need for dcache_lock, as serialization is taken care in * namespace.c */ -static int __follow_mount(struct path *path) +static int __follow_mount(struct path *path, unsigned nofollow) { - int res = 0; - while (d_mountpoint(path->dentry)) { - struct vfsmount *mounted = lookup_mnt(path); - if (!mounted) + struct vfsmount *mounted; + int ret, res = 0; + for (;;) { + while (d_mountpoint(path->dentry)) { + if (nofollow) + return -ELOOP; + 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 (!d_automount_point(path->dentry)) break; - dput(path->dentry); - if (res) - mntput(path->mnt); - path->mnt = mounted; - path->dentry = dget(mounted->mnt_root); + if (nofollow) + return -ELOOP; + ret = follow_automount(path, res); + if (ret < 0) + return ret; res = 1; } - return res; + return 0; } static void follow_mount(struct path *path) @@ -702,6 +749,8 @@ static int do_lookup(struct nameidata *nd, struct qstr *name, struct vfsmount *mnt = nd->path.mnt; struct dentry *dentry, *parent; struct inode *dir; + int ret; + /* * See if the low-level filesystem might want * to use its own hash.. @@ -720,8 +769,10 @@ static int do_lookup(struct nameidata *nd, struct qstr *name, done: path->mnt = mnt; path->dentry = dentry; - __follow_mount(path); - return 0; + ret = __follow_mount(path, 0); + if (unlikely(ret < 0)) + path_put(path); + return ret; need_lookup: parent = nd->path.dentry; @@ -1721,11 +1772,9 @@ 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_mount(path, open_flag & O_NOFOLLOW); + if (error < 0) + goto exit_dput; error = -ENOENT; if (!path->dentry->d_inode) diff --git a/fs/stat.c b/fs/stat.c index 89d72fc..bb0f538 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -43,6 +43,8 @@ void generic_fillattr(struct inode *inode, struct kstat *stat) stat->blocks = inode->i_blocks; stat->blksize = (1 << inode->i_blkbits); stat->inode_flags = inode->i_sb->s_type->inode_flags; + if (IS_AUTOMOUNT(inode)) + stat->inode_flags |= FS_AUTOMOUNT_FL; stat->result_mask |= XSTAT_REQUEST__BASIC_STATS & ~XSTAT_REQUEST_RDEV; if (unlikely(S_ISBLK(stat->mode) || S_ISCHR(stat->mode))) stat->result_mask |= XSTAT_REQUEST_RDEV; diff --git a/include/linux/dcache.h b/include/linux/dcache.h index eebb617..5380bff 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -139,6 +139,7 @@ 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 *); }; /* the dentry parameter passed to d_hash and d_compare is the parent @@ -157,6 +158,7 @@ d_compare: no yes yes no d_delete: no yes no no d_release: no no no yes d_iput: no no no yes +d_automount: no no no yes */ /* d_flags entries */ @@ -389,6 +391,9 @@ static inline int d_mountpoint(struct dentry *dentry) return dentry->d_mounted; } +#define d_automount_point(dentry) \ + (dentry->d_inode && IS_AUTOMOUNT(dentry->d_inode)) + extern struct vfsmount *lookup_mnt(struct path *); extern struct dentry *lookup_create(struct nameidata *nd, int is_dir); diff --git a/include/linux/fs.h b/include/linux/fs.h index 951c36b..579ad9d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -235,6 +235,7 @@ struct inodes_stat_t { #define S_NOCMTIME 128 /* Do not update file c/mtime */ #define S_SWAPFILE 256 /* Do not truncate: swapon got its bmaps */ #define S_PRIVATE 512 /* Inode is fs-internal */ +#define S_AUTOMOUNT 1024 /* Automount/referral quasi-directory */ /* * Note that nosuid etc flags are inode-specific: setting some file-system @@ -269,6 +270,7 @@ struct inodes_stat_t { #define IS_NOCMTIME(inode) ((inode)->i_flags & S_NOCMTIME) #define IS_SWAPFILE(inode) ((inode)->i_flags & S_SWAPFILE) #define IS_PRIVATE(inode) ((inode)->i_flags & S_PRIVATE) +#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. */ -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html