Qu Wenruo
2014-Jul-21 09:02 UTC
[PATCH] btrfs: Add show_path function for btrfs_super_ops.
show_path() function in struct super_operations is used to output
subtree mount info for mountinfo.
Without the implement of show_path() function, user can not found where
each subvolume is mounted if using 'subvolid=' mount option.
(When mounted with 'subvol=' mount option, vfs is aware of subtree mount
and can to the path resolve by vfs itself)
With this patch, end users will be able to use findmnt(8) or other
programs reading mountinfo to find which btrfs subvolume is mounted.
Though we use fs_info->subvol_sem to protect show_path() from subvolume
destroying/creating, if user renames/moves the parent non-subvolume
dir of a subvolume, it is still possible that concurrency may happen and
cause btrfs_search_slot() fails to find the desired key.
In that case, we just return -EBUSY and info user to try again since
extra locking like locking the whole subvolume tree is too expensive for
such usage.
Reported-by: Stefan G.Weichinger <lists@xunil.at>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
---
fs/btrfs/ctree.h | 2 +
fs/btrfs/ioctl.c | 4 +-
fs/btrfs/super.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 116 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index be91397..63fba05 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3881,6 +3881,8 @@ void btrfs_get_block_group_info(struct list_head
*groups_list,
struct btrfs_ioctl_space_info *space);
void update_ioctl_balance_args(struct btrfs_fs_info *fs_info, int lock,
struct btrfs_ioctl_balance_args *bargs);
+int btrfs_search_path_in_tree(struct btrfs_fs_info *info,
+ u64 tree_id, u64 dirid, char *name);
/* file.c */
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 47aceb4..c2bd6b5 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2218,8 +2218,8 @@ static noinline int btrfs_ioctl_tree_search_v2(struct file
*file,
* Search INODE_REFs to identify path name of 'dirid' directory
* in a 'tree_id' tree. and sets path name to 'name'.
*/
-static noinline int btrfs_search_path_in_tree(struct btrfs_fs_info *info,
- u64 tree_id, u64 dirid, char *name)
+int btrfs_search_path_in_tree(struct btrfs_fs_info *info,
+ u64 tree_id, u64 dirid, char *name)
{
struct btrfs_root *root;
struct btrfs_key key;
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 8e16bca..b5ece81 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1831,6 +1831,117 @@ static int btrfs_show_devname(struct seq_file *m, struct
dentry *root)
return 0;
}
+static char *str_prepend(char *dest, char *src)
+{
+ memmove(dest + strlen(src), dest, strlen(dest) + 1);
+ memcpy(dest, src, strlen(src));
+ return dest;
+}
+
+static int alloc_mem_if_needed(char **dest, char *src, int *len)
+{
+ char *tmp;
+
+ if (unlikely(strlen(*dest) + strlen(src) > *len)) {
+ *len *= 2;
+ tmp = krealloc(*dest, *len, GFP_NOFS);
+ if (!tmp) {
+ return -ENOMEM;
+ }
+ *dest = tmp;
+ }
+ return 0;
+}
+
+static int btrfs_show_path(struct seq_file *m, struct dentry *mount_root)
+{
+ struct inode *inode = mount_root->d_inode;
+ struct btrfs_root *subv_root = BTRFS_I(inode)->root;
+ struct btrfs_fs_info *fs_info = subv_root->fs_info;
+ struct btrfs_root *tree_root = fs_info->tree_root;
+ struct btrfs_root_ref *ref;
+ struct btrfs_key key;
+ struct btrfs_key found_key;
+ struct btrfs_path *path = NULL;
+ char *name = NULL;
+ char *buf = NULL;
+ int ret = 0;
+ int len;
+ u64 dirid = 0;
+ u16 namelen;
+
+ name = kmalloc(PAGE_SIZE, GFP_NOFS);
+ len = PAGE_SIZE;
+ buf = kmalloc(BTRFS_INO_LOOKUP_PATH_MAX, GFP_NOFS);
+ path = btrfs_alloc_path();
+ if (!name || !buf || !path) {
+ ret = -ENOMEM;
+ goto out_free;
+ }
+ *name = '/';
+ *(name + 1) = '\0';
+
+ key.objectid = subv_root->root_key.objectid;
+ key.type = BTRFS_ROOT_BACKREF_KEY;
+ key.offset = 0;
+ down_read(&fs_info->subvol_sem);
+ while (key.objectid != BTRFS_FS_TREE_OBJECTID) {
+ ret = btrfs_search_slot_for_read(tree_root, &key, path, 1, 1);
+ if (ret < 0)
+ goto out;
+ if (ret) {
+ ret = -ENOENT;
+ goto out;
+ }
+ btrfs_item_key_to_cpu(path->nodes[0], &found_key,
+ path->slots[0]);
+ if (found_key.objectid != key.objectid ||
+ found_key.type != BTRFS_ROOT_BACKREF_KEY) {
+ ret = -ENOENT;
+ goto out;
+ }
+ /* append the subvol name first */
+ ref = btrfs_item_ptr(path->nodes[0], path->slots[0],
+ struct btrfs_root_ref);
+ dirid = btrfs_root_ref_dirid(path->nodes[0], ref);
+ namelen = btrfs_root_ref_name_len(path->nodes[0], ref);
+ read_extent_buffer(path->nodes[0], buf,
+ (unsigned long)(ref + 1), namelen);
+ *(buf + namelen) = '/';
+ *(buf + namelen + 1) = '\0';
+ ret = alloc_mem_if_needed(&name, buf, &len);
+ if (ret < 0)
+ goto out;
+ str_prepend(name + 1, buf);
+
+ /* then append path name inside the subvole */
+ ret = btrfs_search_path_in_tree(fs_info, found_key.offset,
+ dirid, buf);
+ if (ret < 0) {
+ if (ret == -ENOENT)
+ /* parent dir may be under rename/moving,
+ * info user to try again other than
+ * "No such file or directory" */
+ ret = -EBUSY;
+ goto out;
+ }
+ btrfs_release_path(path);
+ key.objectid = found_key.offset;
+ ret = alloc_mem_if_needed(&name, buf, &len);
+ if (ret < 0)
+ goto out;
+ str_prepend(name + 1, buf);
+ }
+ seq_puts(m, name);
+out:
+ up_read(&fs_info->subvol_sem);
+out_free:
+ btrfs_free_path(path);
+ kfree(buf);
+ kfree(name);
+ return ret;
+}
+
static const struct super_operations btrfs_super_ops = {
.drop_inode = btrfs_drop_inode,
.evict_inode = btrfs_evict_inode,
@@ -1845,6 +1956,7 @@ static const struct super_operations btrfs_super_ops = {
.remount_fs = btrfs_remount,
.freeze_fs = btrfs_freeze,
.unfreeze_fs = btrfs_unfreeze,
+ .show_path = btrfs_show_path,
};
static const struct file_operations btrfs_ctl_fops = {
--
2.0.2
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