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-rw-r--r--Documentation/filesystems/Locking2
-rw-r--r--Documentation/filesystems/vfs.txt14
-rw-r--r--fs/dcache.c5
-rw-r--r--fs/namei.c226
-rw-r--r--include/linux/dcache.h7
-rw-r--r--include/linux/fs.h2
6 files changed, 198 insertions, 58 deletions
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 977d8919cc6..5f0c52a0738 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 cae6d27c9f5..726a4f6fa3c 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 0c6d5c549d8..51f7bb6463a 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 529e917ad2f..16109da68bb 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 59fcd24b146..ee6c26d142c 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 3984f2358d1..4c00ed53be8 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. */
generated by cgit v1.2.3-18-g5258 (git 2.32.0) at 2024-12-26 06:43:05 +0000