Commit 29a8d9a0 authored by Stefan Behrens's avatar Stefan Behrens Committed by Josef Bacik
Browse files

Btrfs: introduce GET_READ_MIRRORS functionality for btrfs_map_block() 



Before this commit, btrfs_map_block() was called with REQ_WRITE
in order to retrieve the list of mirrors for a disk block.
This needs to be changed for the device replace procedure since
it makes a difference whether you are asking for read mirrors
or for locations to write to.
GET_READ_MIRRORS is introduced as a new interface to call
btrfs_map_block().
In the current commit, the functionality is not yet changed,
only the interface for GET_READ_MIRRORS is introduced and all
the places that should use this new interface are adapted.

The reason that REQ_WRITE cannot be abused anymore to retrieve
a list of read mirrors is that during a running dev replace
operation all write requests to the live filesystem are
duplicated to also write to the target drive.
Keep in mind that the target disk is only partially a valid
copy of the source disk while the operation is ongoing. All
writes go to the target disk, but not all reads would return
valid data on the target disk. Therefore it is not possible
anymore to abuse a REQ_WRITE interface to find valid mirrors
for a REQ_READ.

Signed-off-by: default avatarStefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: default avatarChris Mason <chris.mason@fusionio.com>
parent 8dabb742

fs/btrfs/ctree.h

+3 −0
Original line number Diff line number Diff line
@@ -174,6 +174,9 @@ static int btrfs_csum_sizes[] = { 4, 0 }; 
/* four bytes for CRC32 */

#define BTRFS_EMPTY_DIR_SIZE 0



/* spefic to btrfs_map_block(), therefore not in include/linux/blk_types.h */

#define REQ_GET_READ_MIRRORS	(1 << 30)



#define BTRFS_FT_UNKNOWN	0

#define BTRFS_FT_REG_FILE	1

#define BTRFS_FT_DIR		2

fs/btrfs/reada.c

+2 −1
Original line number Diff line number Diff line
@@ -359,7 +359,8 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root, 
	 * map block

	 */

	length = blocksize;

	ret = btrfs_map_block(fs_info, REQ_WRITE, logical, &length, &bbio, 0);

	ret = btrfs_map_block(fs_info, REQ_GET_READ_MIRRORS, logical, &length,

			      &bbio, 0);

	if (ret || !bbio || length < blocksize)

		goto error;

fs/btrfs/scrub.c

+2 −2
Original line number Diff line number Diff line
@@ -1193,8 +1193,8 @@ static int scrub_setup_recheck_block(struct scrub_ctx *sctx, 
		 * with a length of PAGE_SIZE, each returned stripe

		 * represents one mirror

		 */

		ret = btrfs_map_block(fs_info, WRITE, logical, &mapped_length,

				      &bbio, 0);

		ret = btrfs_map_block(fs_info, REQ_GET_READ_MIRRORS, logical,

				      &mapped_length, &bbio, 0);

		if (ret || !bbio || mapped_length < sublen) {

			kfree(bbio);

			return -EIO;

fs/btrfs/volumes.c

+4 −4
Original line number Diff line number Diff line
@@ -4103,7 +4103,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw, 
					    stripe_nr_end - stripe_nr_orig);

		stripe_index = do_div(stripe_nr, map->num_stripes);

	} else if (map->type & BTRFS_BLOCK_GROUP_RAID1) {

		if (rw & (REQ_WRITE | REQ_DISCARD))

		if (rw & (REQ_WRITE | REQ_DISCARD | REQ_GET_READ_MIRRORS))

			num_stripes = map->num_stripes;

		else if (mirror_num)

			stripe_index = mirror_num - 1;
@@ -4115,7 +4115,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw, 
		}



	} else if (map->type & BTRFS_BLOCK_GROUP_DUP) {

		if (rw & (REQ_WRITE | REQ_DISCARD)) {

		if (rw & (REQ_WRITE | REQ_DISCARD | REQ_GET_READ_MIRRORS)) {

			num_stripes = map->num_stripes;

		} else if (mirror_num) {

			stripe_index = mirror_num - 1;
@@ -4129,7 +4129,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw, 
		stripe_index = do_div(stripe_nr, factor);

		stripe_index *= map->sub_stripes;



		if (rw & REQ_WRITE)

		if (rw & (REQ_WRITE | REQ_GET_READ_MIRRORS))

			num_stripes = map->sub_stripes;

		else if (rw & REQ_DISCARD)

			num_stripes = min_t(u64, map->sub_stripes *
@@ -4242,7 +4242,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, int rw, 
		}

	}



	if (rw & REQ_WRITE) {

	if (rw & (REQ_WRITE | REQ_GET_READ_MIRRORS)) {

		if (map->type & (BTRFS_BLOCK_GROUP_RAID1 |

				 BTRFS_BLOCK_GROUP_RAID10 |

				 BTRFS_BLOCK_GROUP_DUP)) {

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