On Wed, Jun 12, 2019 at 02:36:57PM +0800, Qu Wenruo wrote:
> [PROBLEM]
> There are some reports of corrupted fs which can't be mounted due to
> corrupted extent tree.
>
> However under such situation, it's more likely the fs/subvolume trees
> are still fine.
>
> For such case we normally go btrfs-restore and salvage as much as we
> can. However btrfs-restore can't list subvolumes as "btrfs subv list",
> making it harder to restore a fs.
>
> [ENHANCEMENT]
> This patch will introduce a new mount option "rescue=skip_bg" to skip
> the mount time block group scan, and use chunk info purely to populate
> fake block group cache.
>
> The mount option has the following dependency:
> - RO mount
> Obviously.
>
> - No dirty log.
> Either there is no log, or use rescue=no_log_replay mount option.
>
> - No way to remoutn RW
> Similar to rescue=no_log_replay option.
>
> This should allow kernel to accept most extent tree corruption, and
> salvage data and subvolume info.
>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> fs/btrfs/ctree.h | 1 +
> fs/btrfs/disk-io.c | 29 ++++++++++++++++++++----
> fs/btrfs/extent-tree.c | 50 ++++++++++++++++++++++++++++++++++++++++++
> fs/btrfs/super.c | 24 +++++++++++++++++++-
> fs/btrfs/volumes.c | 7 ++++++
> 5 files changed, 106 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 0a61dff27f57..9413db8c9bf0 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1441,6 +1441,7 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct btrfs_fs_info *info)
> #define BTRFS_MOUNT_FREE_SPACE_TREE (1 << 26)
> #define BTRFS_MOUNT_NOLOGREPLAY (1 << 27)
> #define BTRFS_MOUNT_REF_VERIFY (1 << 28)
> +#define BTRFS_MOUNT_SKIP_BG (1 << 29)
>
> #define BTRFS_DEFAULT_COMMIT_INTERVAL (30)
> #define BTRFS_DEFAULT_MAX_INLINE (2048)
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index deb74a8c191a..9701bf8ffbda 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2330,11 +2330,15 @@ static int btrfs_read_roots(struct btrfs_fs_info *fs_info)
>
> root = btrfs_read_tree_root(tree_root, &location);
> if (IS_ERR(root)) {
> - ret = PTR_ERR(root);
> - goto out;
> + if (!btrfs_test_opt(fs_info, SKIP_BG)) {
> + ret = PTR_ERR(root);
> + goto out;
> + }
> + fs_info->extent_root = NULL;
> + } else {
> + set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
> + fs_info->extent_root = root;
> }
> - set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
> - fs_info->extent_root = root;
>
> location.objectid = BTRFS_DEV_TREE_OBJECTID;
> root = btrfs_read_tree_root(tree_root, &location);
> @@ -2956,6 +2960,23 @@ int open_ctree(struct super_block *sb,
> goto fail_alloc;
> }
>
> + /* Skip bg needs RO and no log tree replay */
> + if (btrfs_test_opt(fs_info, SKIP_BG)) {
> + if (!sb_rdonly(sb)) {
> + btrfs_err(fs_info,
> + "skip_bg mount option can only be used with read-only mount");
> + err = -EINVAL;
> + goto fail_alloc;
> + }
> + if (btrfs_super_log_root(disk_super) &&
> + !btrfs_test_opt(fs_info, NOTREELOG)) {
> + btrfs_err(fs_info,
> + "skip_bg must be used with notreelog mount option for dirty log");
> + err = -EINVAL;
> + goto fail_alloc;
> + }
> + }
> +
> ret = btrfs_init_workqueues(fs_info, fs_devices);
> if (ret) {
> err = ret;
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 1aee51a9f3bf..aac9b3ce5224 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -10292,6 +10292,53 @@ static int check_chunk_block_group_mappings(struct btrfs_fs_info *fs_info)
> return ret;
> }
>
> +static int fill_dummy_bgs(struct btrfs_fs_info *fs_info)
> +{
> + struct extent_map_tree *em_tree = &fs_info->mapping_tree.map_tree;
> + struct extent_map *em;
> + struct map_lookup *map;
> + struct btrfs_block_group_cache *cache;
> + struct btrfs_space_info *space_info;
> + struct rb_node *node;
> + int ret = 0;
> +
> + read_lock(&em_tree->lock);
> + for (node = rb_first_cached(&em_tree->map); node;
> + node = rb_next(node)) {
> + em = rb_entry(node, struct extent_map, rb_node);
> + map = em->map_lookup;
> + cache = btrfs_create_block_group_cache(fs_info, em->start,
> + em->len);
> + if (!cache) {
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + /* Fill dummy cache as FULL */
> + cache->flags = map->type;
> + cache->last_byte_to_unpin = (u64)-1;
> + cache->cached = BTRFS_CACHE_FINISHED;
> + btrfs_set_block_group_used(&cache->item, em->len);
> + btrfs_set_block_group_chunk_objectid(&cache->item, em->start);
> + btrfs_set_block_group_flags(&cache->item, map->type);
> + ret = btrfs_add_block_group_cache(fs_info, cache);
> + if (ret) {
> + btrfs_remove_free_space_cache(cache);
> + btrfs_put_block_group(cache);
> + goto out;
> + }
> + update_space_info(fs_info, cache->flags, em->len, em->len,
> + 0, &space_info);
> + cache->space_info = space_info;
> + link_block_group(cache);
> +
> + set_avail_alloc_bits(fs_info, cache->flags);
> + }
> +out:
> + read_unlock(&em_tree->lock);
> + return ret;
> +}
> +
> int btrfs_read_block_groups(struct btrfs_fs_info *info)
> {
> struct btrfs_path *path;
> @@ -10306,6 +10353,9 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
> u64 feature;
> int mixed;
>
> + if (btrfs_test_opt(info, SKIP_BG))
> + return fill_dummy_bgs(info);
> +
> feature = btrfs_super_incompat_flags(info->super_copy);
> mixed = !!(feature & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS);
>
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 4512f25dcf69..f9b33f175e02 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -340,7 +340,7 @@ enum {
> Opt_ref_verify,
> #endif
> /* Rescue options */
> - Opt_rescue, Opt_usebackuproot, Opt_nologreplay,
> + Opt_rescue, Opt_usebackuproot, Opt_nologreplay, Opt_rescue_skip_bg,
> Opt_err,
> };
>
> @@ -416,6 +416,7 @@ static const match_table_t tokens = {
> static const match_table_t rescue_tokens = {
> {Opt_usebackuproot, "use_backup_root"},
> {Opt_nologreplay, "no_log_replay"},
> + {Opt_rescue_skip_bg, "skip_bg"},
> {Opt_err, NULL},
> };
>
> @@ -448,6 +449,10 @@ static int parse_rescue_options(struct btrfs_fs_info *info, const char *options)
> btrfs_set_and_info(info, NOLOGREPLAY,
> "disabling log replay at mount time");
> break;
> + case Opt_rescue_skip_bg:
> + btrfs_set_and_info(info, SKIP_BG,
> + "skip mount time block group searching");
> + break;
> case Opt_err:
> btrfs_info(info, "unrecognized rescue option '%s'", p);
> ret = -EINVAL;
> @@ -1367,6 +1372,8 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
> seq_puts(seq, ",notreelog");
> if (btrfs_test_opt(info, NOLOGREPLAY))
> seq_puts(seq, ",rescue=no_log_replay");
> + if (btrfs_test_opt(info, SKIP_BG))
> + seq_puts(seq, ",rescue=skip_bg");
Now that there are more possible values to print here, they need to
follow the format with the separator.
