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: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 45e7f752b64ac170bf735c86358b4da12cff61b3..46bd7d5f504b3d0dc58a223c0cd472d6880b53fd 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -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

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index c705a48e676b28d3b76eb7c34184daa051e8f2eb..96b93daa0bbb484440e5d51b605ea15884cb9148 100644 (file)
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -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;
 

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 30cbf6921c0baa68aae9a4315f19bfcddb6ec568..30ba99724896cc279a2ea5d1111c39e32384c1fb 100644 (file)
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -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;

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a4e0963bf4573ea5bc0bfec40ce51502172e96f3..de0c05cca3901d18bd208e5f31bd065615d25bff 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -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)) {