* [PATCH V3] Removing a subvolume with a simple "rm -rf"
@ 2010-10-17 16:09 Goffredo Baroncelli
2010-10-18 6:30 ` Ian Kent
0 siblings, 1 reply; 2+ messages in thread
From: Goffredo Baroncelli @ 2010-10-17 16:09 UTC (permalink / raw)
To: linux-btrfs; +Cc: Chris Mason
[-- Attachment #1: Type: text/plain, Size: 4654 bytes --]
Hi all,
enclosed you can find a new version of the patch which permits to remove a
volume via the rmdir(2) syscall by a non-root user. The goal of this patch
is to permits to remove a subvolume with a simple "rm -rf" command.
The rules for a subvolume removal are the same ones of a directory:
- the user must have the write permission on the parent directory
- the subvolume must be empty
The mains differences between calling rmdir(2) on a subvolume and calling the
BTRFS_IOC_SNAP_DESTROY ioctl are:
- rmdir(2) requires the subvolume to be empty (the user has to empty the
subvolume before removing it, like the rm -rf command does)
- rmdir(2) is a synchronous operation (instead BTRFS_IOC_SNAP_DESTROY works
in background)
The previous statements have the following (nice) consequences:
- the CAP_ADMIN capability is not mandatory anymore to remove a subvolume.
BTRFS_IOC_SNAP_DESTROY requires CAP_ADMIN because the subvolume removal is
performed in background so it would not be possible to return an error if
the user has not the privilege of removing a file. This explain why this ioctl
may be executed only by root.
- When the rmdir(2) syscall returns, the space is really freed.
The only advantage of the BTRFS_IOC_SNAP_DESTROY ioctl is its greater speed
in removing a not empty subvolume.
I simplify the code respect my previous post, removing a un-needed call to the
function may_destroy_subvol(). Moreover I added a call to the d_invalidate()
function, which was missed in my previous version.
You can pull the code from the branch named "rmdir-subvolume" of the following
repository:
http://cassiopea.homelinux.net/git/btrfs-unstable.git
As usual, comments are welcome
Regards
G.Baroncelli
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f08427c..f732ddf 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2944,6 +2944,88 @@ int btrfs_unlink_subvol(struct btrfs_trans_handle *trans,
return 0;
}
+static noinline int btrfs_snap_destroy(struct inode *dir,
+ struct dentry *dentry)
+{
+
+ struct inode *inode;
+ struct btrfs_root *root = BTRFS_I(dir)->root;
+ struct btrfs_root *dest = NULL;
+ struct btrfs_trans_handle *trans;
+ int ret;
+ int err = 0;
+
+ if (IS_ERR(dentry)) {
+ err = PTR_ERR(dentry);
+ goto out;
+ }
+
+ if (!dentry->d_inode) {
+ err = -ENOENT;
+ goto out;
+ }
+
+ inode = dentry->d_inode;
+ if (inode->i_ino != BTRFS_FIRST_FREE_OBJECTID) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ dest = BTRFS_I(inode)->root;
+
+ err = d_invalidate(dentry);
+ if (err)
+ goto out;
+
+ down_write(&root->fs_info->subvol_sem);
+
+ /* remove this check because the directory is empty.
+ * err = may_destroy_subvol(dest);
+ * if (err)
+ * goto out_up_write;
+ */
+
+ trans = btrfs_start_transaction(root, 0);
+ if (IS_ERR(trans)) {
+ err = PTR_ERR(trans);
+ goto out_up_write;
+ }
+ trans->block_rsv = &root->fs_info->global_block_rsv;
+
+ ret = btrfs_unlink_subvol(trans, root, dir,
+ dest->root_key.objectid,
+ dentry->d_name.name,
+ dentry->d_name.len);
+ BUG_ON(ret);
+
+ btrfs_record_root_in_trans(trans, dest);
+
+ memset(&dest->root_item.drop_progress, 0,
+ sizeof(dest->root_item.drop_progress));
+ dest->root_item.drop_level = 0;
+ btrfs_set_root_refs(&dest->root_item, 0);
+
+ if (!xchg(&dest->orphan_item_inserted, 1)) {
+ ret = btrfs_insert_orphan_item(trans,
+ root->fs_info->tree_root,
+ dest->root_key.objectid);
+ BUG_ON(ret);
+ }
+
+ ret = btrfs_commit_transaction(trans, root);
+ BUG_ON(ret);
+ inode->i_flags |= S_DEAD;
+out_up_write:
+ up_write(&root->fs_info->subvol_sem);
+ if (!err) {
+ shrink_dcache_sb(root->fs_info->sb);
+ btrfs_invalidate_inodes(dest);
+ /*d_delete(dentry);*/
+ }
+out:
+ return err;
+}
+
static int btrfs_rmdir(struct inode *dir, struct dentry *dentry)
{
struct inode *inode = dentry->d_inode;
@@ -2952,10 +3034,12 @@ static int btrfs_rmdir(struct inode *dir, struct dentry *dentry)
struct btrfs_trans_handle *trans;
unsigned long nr = 0;
- if (inode->i_size > BTRFS_EMPTY_DIR_SIZE ||
- inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
+ if (inode->i_size > BTRFS_EMPTY_DIR_SIZE)
return -ENOTEMPTY;
+ if (inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
+ return btrfs_snap_destroy(dir, dentry);
+
trans = __unlink_start_trans(dir, dentry);
if (IS_ERR(trans))
return PTR_ERR(trans);
--
gpg key@ keyserver.linux.it: Goffredo Baroncelli (ghigo) <kreijackATinwind.it>
Key fingerprint = 4769 7E51 5293 D36C 814E C054 BF04 F161 3DC5 0512
[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 190 bytes --]
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH V3] Removing a subvolume with a simple "rm -rf"
2010-10-17 16:09 [PATCH V3] Removing a subvolume with a simple "rm -rf" Goffredo Baroncelli
@ 2010-10-18 6:30 ` Ian Kent
0 siblings, 0 replies; 2+ messages in thread
From: Ian Kent @ 2010-10-18 6:30 UTC (permalink / raw)
To: kreijack; +Cc: linux-btrfs, Chris Mason
On Sun, 2010-10-17 at 18:09 +0200, Goffredo Baroncelli wrote:
> Hi all,
>
> enclosed you can find a new version of the patch which permits to remove a
> volume via the rmdir(2) syscall by a non-root user. The goal of this patch
> is to permits to remove a subvolume with a simple "rm -rf" command.
>
> The rules for a subvolume removal are the same ones of a directory:
> - the user must have the write permission on the parent directory
> - the subvolume must be empty
>
> The mains differences between calling rmdir(2) on a subvolume and calling the
> BTRFS_IOC_SNAP_DESTROY ioctl are:
>
> - rmdir(2) requires the subvolume to be empty (the user has to empty the
> subvolume before removing it, like the rm -rf command does)
> - rmdir(2) is a synchronous operation (instead BTRFS_IOC_SNAP_DESTROY works
> in background)
>
> The previous statements have the following (nice) consequences:
>
> - the CAP_ADMIN capability is not mandatory anymore to remove a subvolume.
> BTRFS_IOC_SNAP_DESTROY requires CAP_ADMIN because the subvolume removal is
> performed in background so it would not be possible to return an error if
> the user has not the privilege of removing a file. This explain why this ioctl
> may be executed only by root.
>
> - When the rmdir(2) syscall returns, the space is really freed.
>
> The only advantage of the BTRFS_IOC_SNAP_DESTROY ioctl is its greater speed
> in removing a not empty subvolume.
>
> I simplify the code respect my previous post, removing a un-needed call to the
> function may_destroy_subvol(). Moreover I added a call to the d_invalidate()
> function, which was missed in my previous version.
>
> You can pull the code from the branch named "rmdir-subvolume" of the following
> repository:
>
> http://cassiopea.homelinux.net/git/btrfs-unstable.git
>
> As usual, comments are welcome
>
> Regards
> G.Baroncelli
>
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index f08427c..f732ddf 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -2944,6 +2944,88 @@ int btrfs_unlink_subvol(struct btrfs_trans_handle *trans,
> return 0;
> }
>
> +static noinline int btrfs_snap_destroy(struct inode *dir,
> + struct dentry *dentry)
> +{
> +
> + struct inode *inode;
> + struct btrfs_root *root = BTRFS_I(dir)->root;
> + struct btrfs_root *dest = NULL;
> + struct btrfs_trans_handle *trans;
> + int ret;
> + int err = 0;
> +
> + if (IS_ERR(dentry)) {
> + err = PTR_ERR(dentry);
> + goto out;
> + }
> +
> + if (!dentry->d_inode) {
> + err = -ENOENT;
> + goto out;
> + }
> +
> + inode = dentry->d_inode;
> + if (inode->i_ino != BTRFS_FIRST_FREE_OBJECTID) {
> + err = -EINVAL;
> + goto out;
> + }
> +
> + dest = BTRFS_I(inode)->root;
> +
> + err = d_invalidate(dentry);
> + if (err)
> + goto out;
> +
> + down_write(&root->fs_info->subvol_sem);
> +
> + /* remove this check because the directory is empty.
> + * err = may_destroy_subvol(dest);
> + * if (err)
> + * goto out_up_write;
> + */
> +
> + trans = btrfs_start_transaction(root, 0);
> + if (IS_ERR(trans)) {
> + err = PTR_ERR(trans);
> + goto out_up_write;
> + }
Mmm ... sorry to be picky but can this really fail?
Won't you be left with a dentry invisible to the VFS but with an
existing subvol?
> + trans->block_rsv = &root->fs_info->global_block_rsv;
> +
> + ret = btrfs_unlink_subvol(trans, root, dir,
> + dest->root_key.objectid,
> + dentry->d_name.name,
> + dentry->d_name.len);
> + BUG_ON(ret);
What happens if this fails?
Will the file system look corrupt after the reboot, or will the
transaction simply not have been flushed to the disk (ie. not committed
I guess), leaving it looking OK?
> +
> + btrfs_record_root_in_trans(trans, dest);
> +
> + memset(&dest->root_item.drop_progress, 0,
> + sizeof(dest->root_item.drop_progress));
> + dest->root_item.drop_level = 0;
> + btrfs_set_root_refs(&dest->root_item, 0);
> +
> + if (!xchg(&dest->orphan_item_inserted, 1)) {
> + ret = btrfs_insert_orphan_item(trans,
> + root->fs_info->tree_root,
> + dest->root_key.objectid);
> + BUG_ON(ret);
Same Q?
> + }
> +
> + ret = btrfs_commit_transaction(trans, root);
> + BUG_ON(ret);
And again?
> + inode->i_flags |= S_DEAD;
> +out_up_write:
> + up_write(&root->fs_info->subvol_sem);
> + if (!err) {
> + shrink_dcache_sb(root->fs_info->sb);
> + btrfs_invalidate_inodes(dest);
> + /*d_delete(dentry);*/
> + }
> +out:
> + return err;
> +}
> +
> static int btrfs_rmdir(struct inode *dir, struct dentry *dentry)
> {
> struct inode *inode = dentry->d_inode;
> @@ -2952,10 +3034,12 @@ static int btrfs_rmdir(struct inode *dir, struct dentry *dentry)
> struct btrfs_trans_handle *trans;
> unsigned long nr = 0;
>
> - if (inode->i_size > BTRFS_EMPTY_DIR_SIZE ||
> - inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
> + if (inode->i_size > BTRFS_EMPTY_DIR_SIZE)
> return -ENOTEMPTY;
>
> + if (inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
> + return btrfs_snap_destroy(dir, dentry);
> +
> trans = __unlink_start_trans(dir, dentry);
> if (IS_ERR(trans))
> return PTR_ERR(trans);
>
>
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2010-10-17 16:09 [PATCH V3] Removing a subvolume with a simple "rm -rf" Goffredo Baroncelli
2010-10-18 6:30 ` Ian Kent
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