Cleanup btrfs_mount() by using btrfs_mount_root(). This avoids getting
btrfs_mount() called twice in mount path.
Old btrfs_mount() will do:
0. VFS layer calls vfs_kern_mount() with registered file_system_type
(for btrfs, btrfs_fs_type). btrfs_mount() is called on the way.
1. btrfs_parse_early_options() parses "subvolid=" mount option and set the
value to subvol_objectid. Otherwise, subvol_objectid has the initial
value of 0
2. check subvol_objectid is 5 or not. Assume this time id is not 5, then
btrfs_mount() returns by calling mount_subvol()
3. In mount_subvol(), original mount options are modified to contain
"subvolid=0" in setup_root_args(). Then, vfs_kern_mount() is called with
btrfs_fs_type and new options
4. btrfs_mount() is called again
5. btrfs_parse_early_options() parses "subvolid=0" and set 5 (instead of 0)
to subvol_objectid
6. check subvol_objectid is 5 or not. This time id is 5 and mount_subvol()
is not called. btrfs_mount() finishes mounting a root
7. (in mount_subvol()) with using a return vale of vfs_kern_mount(), it
calls mount_subtree()
8. return subvolume's dentry
Reusing the same file_system_type (and btrfs_mount()) for vfs_kern_mount()
is the cause of complication.
Instead, new btrfs_mount() will do:
1. parse subvol id related options for later use in mount_subvol()
2. mount device's root by calling vfs_kern_mount() with
btrfs_root_fs_type, which is not registered to VFS by
register_filesystem(). As a result, btrfs_mount_root() is called
3. return by calling mount_subvol()
The code of 2. is moved from the first part of mount_subvol().
Signed-off-by: Tomohiro Misono <misono.tomoh...@jp.fujitsu.com>
---
fs/btrfs/super.c | 193 +++++++++++++++++++------------------------------------
1 file changed, 65 insertions(+), 128 deletions(-)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 14189ad47466..ce93d87b2a69 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -66,6 +66,11 @@
#include <trace/events/btrfs.h>
static const struct super_operations btrfs_super_ops;
+/*
+ * btrfs_root_fs_type is used internally while
+ * btrfs_fs_type is used for VFS layer.
+ * See the comment at btrfs_mount for more detail.
+ */
static struct file_system_type btrfs_root_fs_type;
static struct file_system_type btrfs_fs_type;
@@ -1404,48 +1409,11 @@ static char *setup_root_args(char *args)
static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
int flags, const char *device_name,
- char *data)
+ char *data, struct vfsmount *mnt)
{
struct dentry *root;
- struct vfsmount *mnt = NULL;
- char *newargs;
int ret;
- newargs = setup_root_args(data);
- if (!newargs) {
- root = ERR_PTR(-ENOMEM);
- goto out;
- }
-
- mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name, newargs);
- if (PTR_ERR_OR_ZERO(mnt) == -EBUSY) {
- if (flags & SB_RDONLY) {
- mnt = vfs_kern_mount(&btrfs_fs_type, flags & ~SB_RDONLY,
- device_name, newargs);
- } else {
- mnt = vfs_kern_mount(&btrfs_fs_type, flags | SB_RDONLY,
- device_name, newargs);
- if (IS_ERR(mnt)) {
- root = ERR_CAST(mnt);
- mnt = NULL;
- goto out;
- }
-
- down_write(&mnt->mnt_sb->s_umount);
- ret = btrfs_remount(mnt->mnt_sb, &flags, NULL);
- up_write(&mnt->mnt_sb->s_umount);
- if (ret < 0) {
- root = ERR_PTR(ret);
- goto out;
- }
- }
- }
- if (IS_ERR(mnt)) {
- root = ERR_CAST(mnt);
- mnt = NULL;
- goto out;
- }
-
if (!subvol_name) {
if (!subvol_objectid) {
ret = get_default_subvol_objectid(btrfs_sb(mnt->mnt_sb),
@@ -1501,7 +1469,6 @@ static struct dentry *mount_subvol(const char
*subvol_name, u64 subvol_objectid,
out:
mntput(mnt);
- kfree(newargs);
kfree(subvol_name);
return root;
}
@@ -1556,6 +1523,12 @@ static int setup_security_options(struct btrfs_fs_info
*fs_info,
return ret;
}
+/*
+ * Find a superblock for the given device / mount point.
+ *
+ * Note: This is based on mount_bdev from fs/super.c with a few additions
+ * for multiple device setup. Make sure to keep it in sync.
+ */
static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
int flags, const char *device_name, void *data)
{
@@ -1662,20 +1635,35 @@ static struct dentry *btrfs_mount_root(struct
file_system_type *fs_type,
security_free_mnt_opts(&new_sec_opts);
return ERR_PTR(error);
}
+
/*
- * Find a superblock for the given device / mount point.
+ * Mount function which is called by VFS layer.
+ *
+ * In order to allow mounting a subvolume directly, btrfs uses
+ * mount_subtree() which needs vfsmount* of device's root (/).
+ * This means device's root has to be mounted internally in any case.
+ *
+ * Operation flow:
+ * 1. Parse subvol id related options for later use in mount_subvol().
+ *
+ * 2. Mount device's root (/) by calling vfs_kern_mount().
*
- * Note: This is based on get_sb_bdev from fs/super.c with a few additions
- * for multiple device setup. Make sure to keep it in sync.
+ * NOTE: vfs_kern_mount() is used by VFS to call btrfs_mount() in the
+ * first place. In order to avoid calling btrfs_mount() again, we use
+ * different file_system_type which is not registered to VFS by
+ * register_filesystem() (btrfs_root_fs_type). As a result,
+ * btrfs_mount_root() is called. The return value will be used by
+ * mount_subtree() in mount_subvol().
+ *
+ * 3. Call mount_subvol() to get the dentry of subvolume. Since there is
+ * "btrfs subvolume set-default", mount_subvol() is called always.
*/
static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
const char *device_name, void *data)
{
- struct block_device *bdev = NULL;
- struct super_block *s;
struct btrfs_fs_devices *fs_devices = NULL;
- struct btrfs_fs_info *fs_info = NULL;
- struct security_mnt_opts new_sec_opts;
+ struct vfsmount *mnt_root;
+ struct dentry *root;
fmode_t mode = FMODE_READ;
char *subvol_name = NULL;
u64 subvol_objectid = 0;
@@ -1692,93 +1680,42 @@ static struct dentry *btrfs_mount(struct
file_system_type *fs_type, int flags,
return ERR_PTR(error);
}
- if (subvol_name || subvol_objectid != BTRFS_FS_TREE_OBJECTID) {
- /* mount_subvol() will free subvol_name. */
- return mount_subvol(subvol_name, subvol_objectid, flags,
- device_name, data);
- }
-
- security_init_mnt_opts(&new_sec_opts);
- if (data) {
- error = parse_security_options(data, &new_sec_opts);
- if (error)
- return ERR_PTR(error);
- }
-
- error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
- if (error)
- goto error_sec_opts;
-
- /*
- * Setup a dummy root and fs_info for test/set super. This is because
- * we don't actually fill this stuff out until open_ctree, but we need
- * it for searching for existing supers, so this lets us do that and
- * then open_ctree will properly initialize everything later.
- */
- fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_KERNEL);
- if (!fs_info) {
- error = -ENOMEM;
- goto error_sec_opts;
- }
-
- fs_info->fs_devices = fs_devices;
-
- fs_info->super_copy = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_KERNEL);
- fs_info->super_for_commit = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_KERNEL);
- security_init_mnt_opts(&fs_info->security_opts);
- if (!fs_info->super_copy || !fs_info->super_for_commit) {
- error = -ENOMEM;
- goto error_fs_info;
- }
-
- error = btrfs_open_devices(fs_devices, mode, fs_type);
- if (error)
- goto error_fs_info;
-
- if (!(flags & SB_RDONLY) && fs_devices->rw_devices == 0) {
- error = -EACCES;
- goto error_close_devices;
- }
-
- bdev = fs_devices->latest_bdev;
- s = sget(fs_type, btrfs_test_super, btrfs_set_super, flags | SB_NOSEC,
- fs_info);
- if (IS_ERR(s)) {
- error = PTR_ERR(s);
- goto error_close_devices;
- }
+ /* mount device's root (/) */
+ mnt_root = vfs_kern_mount(&btrfs_root_fs_type, flags,
+ device_name, data);
+ if (PTR_ERR_OR_ZERO(mnt_root) == -EBUSY) {
+ if (flags & SB_RDONLY) {
+ mnt_root = vfs_kern_mount(&btrfs_root_fs_type,
+ flags & ~SB_RDONLY, device_name, data);
+ } else {
+ mnt_root = vfs_kern_mount(&btrfs_root_fs_type,
+ flags | SB_RDONLY, device_name, data);
+ if (IS_ERR(mnt_root)) {
+ root = ERR_CAST(mnt_root);
+ goto out;
+ }
- if (s->s_root) {
- btrfs_close_devices(fs_devices);
- free_fs_info(fs_info);
- if ((flags ^ s->s_flags) & SB_RDONLY)
- error = -EBUSY;
- } else {
- snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
- btrfs_sb(s)->bdev_holder = fs_type;
- error = btrfs_fill_super(s, fs_devices, data);
- }
- if (error) {
- deactivate_locked_super(s);
- goto error_sec_opts;
+ down_write(&mnt_root->mnt_sb->s_umount);
+ error = btrfs_remount(mnt_root->mnt_sb, &flags, NULL);
+ up_write(&mnt_root->mnt_sb->s_umount);
+ if (error < 0) {
+ root = ERR_PTR(error);
+ mntput(mnt_root);
+ goto out;
+ }
+ }
}
-
- fs_info = btrfs_sb(s);
- error = setup_security_options(fs_info, s, &new_sec_opts);
- if (error) {
- deactivate_locked_super(s);
- goto error_sec_opts;
+ if (IS_ERR(mnt_root)) {
+ root = ERR_CAST(mnt_root);
+ goto out;
}
- return dget(s->s_root);
+ /* mount_subvol() will free subvol_name and mnt_root */
+ root = mount_subvol(subvol_name, subvol_objectid, flags,
+ device_name, data, mnt_root);
-error_close_devices:
- btrfs_close_devices(fs_devices);
-error_fs_info:
- free_fs_info(fs_info);
-error_sec_opts:
- security_free_mnt_opts(&new_sec_opts);
- return ERR_PTR(error);
+out:
+ return root;
}
static void btrfs_resize_thread_pool(struct btrfs_fs_info *fs_info,
