We use merge_bvec_fn to make sure that copies do not split internal
boundaries of device mapper devices.
There is no possibility to split a copy bio (splitting would complicate
the design significantly), so we must use merge_bvec_fn to make sure that
the bios have appropriate size for the device mapper stack.
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
---
block/blk-lib.c | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
Index: linux-3.16-rc5/block/blk-lib.c
===================================================================
--- linux-3.16-rc5.orig/block/blk-lib.c 2014-07-15 15:27:51.000000000 +0200
+++ linux-3.16-rc5/block/blk-lib.c 2014-07-15 15:27:59.000000000 +0200
@@ -369,6 +369,31 @@ static void bio_copy_end_io(struct bio *
}
}
+static unsigned blkdev_copy_merge(struct block_device *bdev,
+ struct request_queue *q, unsigned long bi_rw,
+ sector_t sector, unsigned n)
+{
+ if (!q->merge_bvec_fn) {
+ return n;
+ } else {
+ unsigned m;
+ struct bvec_merge_data bvm = {
+ .bi_bdev = bdev,
+ .bi_sector = sector,
+ .bi_size = 0,
+ .bi_rw = bi_rw,
+ };
+ struct bio_vec vec = {
+ .bv_page = NULL,
+ .bv_len = likely(n <= UINT_MAX >> 9) ? n << 9 :
UINT_MAX & ~511U,
+ .bv_offset = 0,
+ };
+ m = q->merge_bvec_fn(q, &bvm, &vec);
+ m >>= 9;
+ return min(m, n);
+ }
+}
+
/**
* blkdev_issue_copy - queue a copy same operation
* @src_bdev: source blockdev
@@ -424,6 +449,18 @@ int blkdev_issue_copy(struct block_devic
struct bio_copy *bc;
unsigned chunk = (unsigned)min(nr_sects,
(sector_t)max_copy_sectors);
+ chunk = blkdev_copy_merge(src_bdev, sq, READ | REQ_COPY,
src_sector, chunk);
+ if (!chunk) {
+ ret = -EOPNOTSUPP;
+ break;
+ }
+
+ chunk = blkdev_copy_merge(dst_bdev, dq, WRITE | REQ_COPY,
dst_sector, chunk);
+ if (!chunk) {
+ ret = -EOPNOTSUPP;
+ break;
+ }
+
bc = kmalloc(sizeof(struct bio_copy), gfp_mask);
if (!bc) {
ret = -ENOMEM;
--
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