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Btrfs: unify subvol= and subvolid= mounting
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Currently, mounting a subvolume with subvolid= takes a different code
path than mounting with subvol=. This isn't really a big deal except for
the fact that mounts done with subvolid= or the default subvolume don't
have a dentry that's connected to the dentry tree like in the subvol=
case. To unify the code paths, when given subvolid= or using the default
subvolume ID, translate it into a subvolume name by walking
ROOT_BACKREFs in the root tree and INODE_REFs in the filesystem trees.

Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Chris Mason <clm@fb.com>
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Omar Sandoval authored and Chris Mason committed Jun 3, 2015
1 parent bb289b7 commit 05dbe68
Showing 1 changed file with 171 additions and 67 deletions.
238 changes: 171 additions & 67 deletions fs/btrfs/super.c
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Original file line number Diff line number Diff line change
Expand Up @@ -836,33 +836,153 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
return error;
}

static struct dentry *get_default_root(struct super_block *sb,
u64 subvol_objectid)
static char *get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
u64 subvol_objectid)
{
struct btrfs_fs_info *fs_info = btrfs_sb(sb);
struct btrfs_root *root = fs_info->tree_root;
struct btrfs_root *new_root;
struct btrfs_dir_item *di;
struct btrfs_path *path;
struct btrfs_key location;
struct inode *inode;
u64 dir_id;
int new = 0;
struct btrfs_root *fs_root;
struct btrfs_root_ref *root_ref;
struct btrfs_inode_ref *inode_ref;
struct btrfs_key key;
struct btrfs_path *path = NULL;
char *name = NULL, *ptr;
u64 dirid;
int len;
int ret;

path = btrfs_alloc_path();
if (!path) {
ret = -ENOMEM;
goto err;
}
path->leave_spinning = 1;

name = kmalloc(PATH_MAX, GFP_NOFS);
if (!name) {
ret = -ENOMEM;
goto err;
}
ptr = name + PATH_MAX - 1;
ptr[0] = '\0';

/*
* We have a specific subvol we want to mount, just setup location and
* go look up the root.
* Walk up the subvolume trees in the tree of tree roots by root
* backrefs until we hit the top-level subvolume.
*/
if (subvol_objectid) {
location.objectid = subvol_objectid;
location.type = BTRFS_ROOT_ITEM_KEY;
location.offset = (u64)-1;
goto find_root;
while (subvol_objectid != BTRFS_FS_TREE_OBJECTID) {
key.objectid = subvol_objectid;
key.type = BTRFS_ROOT_BACKREF_KEY;
key.offset = (u64)-1;

ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
if (ret < 0) {
goto err;
} else if (ret > 0) {
ret = btrfs_previous_item(root, path, subvol_objectid,
BTRFS_ROOT_BACKREF_KEY);
if (ret < 0) {
goto err;
} else if (ret > 0) {
ret = -ENOENT;
goto err;
}
}

btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
subvol_objectid = key.offset;

root_ref = btrfs_item_ptr(path->nodes[0], path->slots[0],
struct btrfs_root_ref);
len = btrfs_root_ref_name_len(path->nodes[0], root_ref);
ptr -= len + 1;
if (ptr < name) {
ret = -ENAMETOOLONG;
goto err;
}
read_extent_buffer(path->nodes[0], ptr + 1,
(unsigned long)(root_ref + 1), len);
ptr[0] = '/';
dirid = btrfs_root_ref_dirid(path->nodes[0], root_ref);
btrfs_release_path(path);

key.objectid = subvol_objectid;
key.type = BTRFS_ROOT_ITEM_KEY;
key.offset = (u64)-1;
fs_root = btrfs_read_fs_root_no_name(fs_info, &key);
if (IS_ERR(fs_root)) {
ret = PTR_ERR(fs_root);
goto err;
}

/*
* Walk up the filesystem tree by inode refs until we hit the
* root directory.
*/
while (dirid != BTRFS_FIRST_FREE_OBJECTID) {
key.objectid = dirid;
key.type = BTRFS_INODE_REF_KEY;
key.offset = (u64)-1;

ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
if (ret < 0) {
goto err;
} else if (ret > 0) {
ret = btrfs_previous_item(fs_root, path, dirid,
BTRFS_INODE_REF_KEY);
if (ret < 0) {
goto err;
} else if (ret > 0) {
ret = -ENOENT;
goto err;
}
}

btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
dirid = key.offset;

inode_ref = btrfs_item_ptr(path->nodes[0],
path->slots[0],
struct btrfs_inode_ref);
len = btrfs_inode_ref_name_len(path->nodes[0],
inode_ref);
ptr -= len + 1;
if (ptr < name) {
ret = -ENAMETOOLONG;
goto err;
}
read_extent_buffer(path->nodes[0], ptr + 1,
(unsigned long)(inode_ref + 1), len);
ptr[0] = '/';
btrfs_release_path(path);
}
}

btrfs_free_path(path);
if (ptr == name + PATH_MAX - 1) {
name[0] = '/';
name[1] = '\0';
} else {
memmove(name, ptr, name + PATH_MAX - ptr);
}
return name;

err:
btrfs_free_path(path);
kfree(name);
return ERR_PTR(ret);
}

static int get_default_subvol_objectid(struct btrfs_fs_info *fs_info, u64 *objectid)
{
struct btrfs_root *root = fs_info->tree_root;
struct btrfs_dir_item *di;
struct btrfs_path *path;
struct btrfs_key location;
u64 dir_id;

path = btrfs_alloc_path();
if (!path)
return ERR_PTR(-ENOMEM);
return -ENOMEM;
path->leave_spinning = 1;

/*
Expand All @@ -874,58 +994,23 @@ static struct dentry *get_default_root(struct super_block *sb,
di = btrfs_lookup_dir_item(NULL, root, path, dir_id, "default", 7, 0);
if (IS_ERR(di)) {
btrfs_free_path(path);
return ERR_CAST(di);
return PTR_ERR(di);
}
if (!di) {
/*
* Ok the default dir item isn't there. This is weird since
* it's always been there, but don't freak out, just try and
* mount to root most subvolume.
* mount the top-level subvolume.
*/
btrfs_free_path(path);
dir_id = BTRFS_FIRST_FREE_OBJECTID;
new_root = fs_info->fs_root;
goto setup_root;
*objectid = BTRFS_FS_TREE_OBJECTID;
return 0;
}

btrfs_dir_item_key_to_cpu(path->nodes[0], di, &location);
btrfs_free_path(path);

find_root:
new_root = btrfs_read_fs_root_no_name(fs_info, &location);
if (IS_ERR(new_root))
return ERR_CAST(new_root);

if (!(sb->s_flags & MS_RDONLY)) {
int ret;
down_read(&fs_info->cleanup_work_sem);
ret = btrfs_orphan_cleanup(new_root);
up_read(&fs_info->cleanup_work_sem);
if (ret)
return ERR_PTR(ret);
}

dir_id = btrfs_root_dirid(&new_root->root_item);
setup_root:
location.objectid = dir_id;
location.type = BTRFS_INODE_ITEM_KEY;
location.offset = 0;

inode = btrfs_iget(sb, &location, new_root, &new);
if (IS_ERR(inode))
return ERR_CAST(inode);

/*
* If we're just mounting the root most subvol put the inode and return
* a reference to the dentry. We will have already gotten a reference
* to the inode in btrfs_fill_super so we're good to go.
*/
if (!new && d_inode(sb->s_root) == inode) {
iput(inode);
return dget(sb->s_root);
}

return d_obtain_root(inode);
*objectid = location.objectid;
return 0;
}

static int btrfs_fill_super(struct super_block *sb,
Expand Down Expand Up @@ -1211,6 +1296,25 @@ static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
goto out;
}

if (!subvol_name) {
if (!subvol_objectid) {
ret = get_default_subvol_objectid(btrfs_sb(mnt->mnt_sb),
&subvol_objectid);
if (ret) {
root = ERR_PTR(ret);
goto out;
}
}
subvol_name = get_subvol_name_from_objectid(btrfs_sb(mnt->mnt_sb),
subvol_objectid);
if (IS_ERR(subvol_name)) {
root = ERR_CAST(subvol_name);
subvol_name = NULL;
goto out;
}

}

root = mount_subtree(mnt, subvol_name);
/* mount_subtree() drops our reference on the vfsmount. */
mnt = NULL;
Expand All @@ -1227,6 +1331,11 @@ static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
ret = -EINVAL;
}
if (subvol_objectid && root_objectid != subvol_objectid) {
/*
* This will also catch a race condition where a
* subvolume which was passed by ID is renamed and
* another subvolume is renamed over the old location.
*/
pr_err("BTRFS: subvol '%s' does not match subvolid %llu\n",
subvol_name, subvol_objectid);
ret = -EINVAL;
Expand Down Expand Up @@ -1306,7 +1415,6 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
{
struct block_device *bdev = NULL;
struct super_block *s;
struct dentry *root;
struct btrfs_fs_devices *fs_devices = NULL;
struct btrfs_fs_info *fs_info = NULL;
struct security_mnt_opts new_sec_opts;
Expand All @@ -1326,7 +1434,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
return ERR_PTR(error);
}

if (subvol_name) {
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);
Expand Down Expand Up @@ -1395,23 +1503,19 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
error = btrfs_fill_super(s, fs_devices, data,
flags & MS_SILENT ? 1 : 0);
}

root = !error ? get_default_root(s, subvol_objectid) : ERR_PTR(error);
if (IS_ERR(root)) {
if (error) {
deactivate_locked_super(s);
error = PTR_ERR(root);
goto error_sec_opts;
}

fs_info = btrfs_sb(s);
error = setup_security_options(fs_info, s, &new_sec_opts);
if (error) {
dput(root);
deactivate_locked_super(s);
goto error_sec_opts;
}

return root;
return dget(s->s_root);

error_close_devices:
btrfs_close_devices(fs_devices);
Expand Down

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