[PATCH 4/8] btrfs: autoremove qgroup by default, and add a mount flag to override

[Sargun Dhillon <sargun@sargun.me>]

This change follows the change to automatically remove qgroups
if the associated subvolume has also been removed. It changes
the default behaviour to automatically remove qgroups when
a subvolume is deleted, but this can be override with the
qgroup_keep mount flag.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>
---
 fs/btrfs/ctree.h |  1 +
 fs/btrfs/ioctl.c | 14 ++++++++++++++
 fs/btrfs/super.c | 16 +++++++++++++++-
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 643c70d..4d57eb6 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1348,6 +1348,7 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct btrfs_fs_info *info)
 #define BTRFS_MOUNT_FRAGMENT_METADATA	(1 << 25)
 #define BTRFS_MOUNT_FREE_SPACE_TREE	(1 << 26)
 #define BTRFS_MOUNT_NOLOGREPLAY		(1 << 27)
+#define BTRFS_MOUNT_QGROUP_KEEP		(1 << 28)
 
 #define BTRFS_DEFAULT_COMMIT_INTERVAL	(30)
 #define BTRFS_DEFAULT_MAX_INLINE	(2048)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index e176375..b10d7bb 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2544,6 +2544,20 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 		}
 	}
 
+	/*
+	 * Attempt to automatically remove the automatically attached qgroup
+	 * setup in btrfs_qgroup_inherit. As a matter of convention, the id
+	 * is the same as the subvolume id.
+	 *
+	 * This can fail non-fatally for level 0 qgroups, and potentially
+	 * leave the filesystem in an awkward, (but working) state.
+	 */
+	if (!btrfs_test_opt(fs_info, QGROUP_KEEP)) {
+		ret = btrfs_remove_qgroup(trans, fs_info,
+					  dest->root_key.objectid);
+		if (ret && ret != -ENOENT)
+			pr_info("Could not automatically delete qgroup: %d\n", ret);
+	}
 out_end_trans:
 	trans->block_rsv = NULL;
 	trans->bytes_reserved = 0;
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 4f1cdd5..232e1b8 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -321,7 +321,7 @@ enum {
 	Opt_commit_interval, Opt_barrier, Opt_nodefrag, Opt_nodiscard,
 	Opt_noenospc_debug, Opt_noflushoncommit, Opt_acl, Opt_datacow,
 	Opt_datasum, Opt_treelog, Opt_noinode_cache, Opt_usebackuproot,
-	Opt_nologreplay, Opt_norecovery,
+	Opt_nologreplay, Opt_norecovery, Opt_qgroup_keep, Opt_qgroup_nokeep,
 #ifdef CONFIG_BTRFS_DEBUG
 	Opt_fragment_data, Opt_fragment_metadata, Opt_fragment_all,
 #endif
@@ -381,6 +381,8 @@ static const match_table_t tokens = {
 	{Opt_rescan_uuid_tree, "rescan_uuid_tree"},
 	{Opt_fatal_errors, "fatal_errors=%s"},
 	{Opt_commit_interval, "commit=%d"},
+	{Opt_qgroup_keep, "qgroup_keep"},
+	{Opt_qgroup_nokeep, "qgroup_nokeep"},
 #ifdef CONFIG_BTRFS_DEBUG
 	{Opt_fragment_data, "fragment=data"},
 	{Opt_fragment_metadata, "fragment=metadata"},
@@ -808,6 +810,14 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 				info->commit_interval = BTRFS_DEFAULT_COMMIT_INTERVAL;
 			}
 			break;
+		case Opt_qgroup_keep:
+			btrfs_set_and_info(info, QGROUP_KEEP,
+					   "do not automatically delete qgroups");
+			break;
+		case Opt_qgroup_nokeep:
+			btrfs_clear_and_info(info, QGROUP_KEEP,
+					     "automatically delete qgroups");
+			break;
 #ifdef CONFIG_BTRFS_DEBUG
 		case Opt_fragment_all:
 			btrfs_info(info, "fragmenting all space");
@@ -1299,6 +1309,10 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
 		seq_puts(seq, ",fatal_errors=panic");
 	if (info->commit_interval != BTRFS_DEFAULT_COMMIT_INTERVAL)
 		seq_printf(seq, ",commit=%d", info->commit_interval);
+	if (btrfs_test_opt(info, QGROUP_KEEP))
+		seq_puts(seq, ",qgroup_keep");
+	else
+		seq_puts(seq, ",qgroup_nokeep");
 #ifdef CONFIG_BTRFS_DEBUG
 	if (btrfs_test_opt(info, FRAGMENT_DATA))
 		seq_puts(seq, ",fragment=data");
-- 
2.9.3