[v3,1/7] btrfs: Introduce a function to check if all chunks a OK for degraded rw mount

Commit Message

Qu Wenruo March 8, 2017, 2:41 a.m. UTC

Introduce a new function, btrfs_check_rw_degradable(), to check if all
chunks in btrfs is OK for degraded rw mount.

It provides the new basis for accurate btrfs mount/remount and even
runtime degraded mount check other than old one-size-fit-all method.

Signed-off-by: Qu Wenruo <[e-mail]>
Reviewed-by: Anand Jain <[e-mail]>
---
 fs/btrfs/volumes.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/volumes.h |  1 +
 2 files changed, 54 insertions(+)

Patch

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 73d56eef5e60..3fb760cd5bad 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6765,6 +6765,59 @@  int btrfs_read_sys_array(struct btrfs_fs_info *fs_info)
 	return -EIO;
 }
 
+/*
+ * Check if all chunks in the fs is OK for read-write degraded mount
+ *
+ * Return true if the fs is OK to be mounted degraded read-write
+ * Return false if the fs is not OK to be mounted degraded
+ */
+bool btrfs_check_rw_degradable(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
+	struct extent_map *em;
+	u64 next_start = 0;
+	bool ret = true;
+
+	read_lock(&map_tree->map_tree.lock);
+	em = lookup_extent_mapping(&map_tree->map_tree, 0, (u64)-1);
+	/* No chunk at all? Return false anyway */
+	if (!em) {
+		ret = false;
+		goto out;
+	}
+	while (em) {
+		struct map_lookup *map;
+		int missing = 0;
+		int max_tolerated;
+		int i;
+
+		map = (struct map_lookup *) em->bdev;
+		max_tolerated =
+			btrfs_get_num_tolerated_disk_barrier_failures(
+					map->type);
+		for (i = 0; i < map->num_stripes; i++) {
+			if (map->stripes[i].dev->missing)
+				missing++;
+		}
+		if (missing > max_tolerated) {
+			ret = false;
+			btrfs_warn(fs_info,
+	"chunk %llu missing %d devices, max tolerance is %d for writeble mount",
+				   em->start, missing, max_tolerated);
+			free_extent_map(em);
+			goto out;
+		}
+		next_start = extent_map_end(em);
+		free_extent_map(em);
+
+		em = lookup_extent_mapping(&map_tree->map_tree, next_start,
+					   (u64)(-1) - next_start);
+	}
+out:
+	read_unlock(&map_tree->map_tree.lock);
+	return ret;
+}
+
 int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_root *root = fs_info->chunk_root;
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 59be81206dd7..db1b5ef479cf 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -538,4 +538,5 @@  struct list_head *btrfs_get_fs_uuids(void);
 void btrfs_set_fs_info_ptr(struct btrfs_fs_info *fs_info);
 void btrfs_reset_fs_info_ptr(struct btrfs_fs_info *fs_info);
 
+bool btrfs_check_rw_degradable(struct btrfs_fs_info *fs_info);
 #endif