[PATCH][v2] btrfs-progs: add a --check-bg-usage option to fsck

[Josef Bacik <josef@toxicpanda.com>]

Sometimes when messing with the chunk allocator code we can end up
over-allocating chunks.  Generally speaking I'll notice this when a
random xfstest fails with ENOSPC when it shouldn't, but I'm super
worried that I won't catch a problem until somebody has a fs completely
filled up with empty block groups.  Add a fsck option to check for too
many empty block groups.  This way I can set FSCK_OPTIONS="-B" to catch
cases where we're too aggressive with the chunk allocator but not so
aggressive that it causes problems in xfstests.

Thankfully this doesn't trip up currently, so this will just keep me
from regressing us.  Thanks,

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
v1->v2:
- tested with my alloc chunk ioctl, realized the chunk checker removes the bg
  recs from the list, so this wasn't actually doing anything.  Moved the check
  so now it properly fails on a bad fs.

 btrfsck.h    |  1 +
 check/main.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/btrfsck.h b/btrfsck.h
index ac7f5d48..5e779075 100644
--- a/btrfsck.h
+++ b/btrfsck.h
@@ -44,6 +44,7 @@ struct block_group_record {
 	u64 offset;
 
 	u64 flags;
+	u64 used;
 };
 
 struct block_group_tree {
diff --git a/check/main.c b/check/main.c
index 0cc6fdba..ca2ace10 100644
--- a/check/main.c
+++ b/check/main.c
@@ -62,6 +62,7 @@ int no_holes = 0;
 static int is_free_space_tree = 0;
 int init_extent_tree = 0;
 int check_data_csum = 0;
+int check_bg_usage = 0;
 struct btrfs_fs_info *global_info;
 struct task_ctx ctx = { 0 };
 struct cache_tree *roots_info_cache = NULL;
@@ -5126,6 +5127,7 @@ btrfs_new_block_group_record(struct extent_buffer *leaf, struct btrfs_key *key,
 
 	ptr = btrfs_item_ptr(leaf, slot, struct btrfs_block_group_item);
 	rec->flags = btrfs_disk_block_group_flags(leaf, ptr);
+	rec->used = btrfs_disk_block_group_used(leaf, ptr);
 
 	INIT_LIST_HEAD(&rec->list);
 
@@ -8522,6 +8524,41 @@ out:
 	return ret;
 }
 
+static int check_block_group_usage(struct block_group_tree *block_group_cache)
+{
+	struct block_group_record *bg_rec;
+	int empty_data = 0, empty_metadata = 0, empty_system = 0;
+	int ret = 0;
+
+	list_for_each_entry(bg_rec, &block_group_cache->block_groups, list) {
+		if (bg_rec->used)
+			continue;
+		if (bg_rec->flags & BTRFS_BLOCK_GROUP_DATA)
+			empty_data++;
+		else if (bg_rec->flags & BTRFS_BLOCK_GROUP_METADATA)
+			empty_metadata++;
+		else
+			empty_system++;
+	}
+
+	if (empty_data > 1) {
+		ret = -EINVAL;
+		fprintf(stderr, "Too many empty data block groups: %d\n",
+			empty_data);
+	}
+	if (empty_metadata > 1) {
+		ret = -EINVAL;
+		fprintf(stderr, "Too many empty metadata block groups: %d\n",
+			empty_metadata);
+	}
+	if (empty_system > 1) {
+		ret = -EINVAL;
+		fprintf(stderr, "Too many empty system block groups: %d\n",
+			empty_system);
+	}
+	return ret;
+}
+
 static int check_chunks_and_extents(struct btrfs_fs_info *fs_info)
 {
 	struct rb_root dev_cache;
@@ -8622,6 +8659,13 @@ again:
 		goto out;
 	}
 
+	if (check_bg_usage) {
+		ret = check_block_group_usage(&block_group_cache);
+		if (ret)
+			err = ret;
+		goto out;
+	}
+
 	ret = check_chunks(&chunk_cache, &block_group_cache,
 			   &dev_extent_cache, NULL, NULL, NULL, 0);
 	if (ret) {
@@ -9810,6 +9854,7 @@ static const char * const cmd_check_usage[] = {
 	"       -E|--subvol-extents <subvolid>",
 	"                                   print subvolume extents and sharing state",
 	"       -p|--progress               indicate progress",
+	"       -B|--check-bg-usage         check for too many empty block groups",
 	NULL
 };
 
@@ -9841,7 +9886,7 @@ static int cmd_check(const struct cmd_struct *cmd, int argc, char **argv)
 			GETOPT_VAL_INIT_EXTENT, GETOPT_VAL_CHECK_CSUM,
 			GETOPT_VAL_READONLY, GETOPT_VAL_CHUNK_TREE,
 			GETOPT_VAL_MODE, GETOPT_VAL_CLEAR_SPACE_CACHE,
-			GETOPT_VAL_FORCE };
+			GETOPT_VAL_FORCE};
 		static const struct option long_options[] = {
 			{ "super", required_argument, NULL, 's' },
 			{ "repair", no_argument, NULL, GETOPT_VAL_REPAIR },
@@ -9864,10 +9909,11 @@ static int cmd_check(const struct cmd_struct *cmd, int argc, char **argv)
 			{ "clear-space-cache", required_argument, NULL,
 				GETOPT_VAL_CLEAR_SPACE_CACHE},
 			{ "force", no_argument, NULL, GETOPT_VAL_FORCE },
+			{ "check-bg-usage", no_argument, NULL, 'B' },
 			{ NULL, 0, NULL, 0}
 		};
 
-		c = getopt_long(argc, argv, "as:br:pEQ", long_options, NULL);
+		c = getopt_long(argc, argv, "as:br:pEQB", long_options, NULL);
 		if (c < 0)
 			break;
 		switch(c) {
@@ -9875,6 +9921,9 @@ static int cmd_check(const struct cmd_struct *cmd, int argc, char **argv)
 			case 'b':
 				ctree_flags |= OPEN_CTREE_BACKUP_ROOT;
 				break;
+			case 'B':
+				check_bg_usage = 1;
+				break;
 			case 's':
 				num = arg_strtou64(optarg);
 				if (num >= BTRFS_SUPER_MIRROR_MAX) {
-- 
2.21.0