[Qemu-devel] [PATCH 1/4] block: Add bdrv_get_request_alignment()

[Eric Blake]

The next patch needs access to a device's minimum permitted
alignment, since NBD wants to advertise this to clients. Add
an accessor function, borrowing from blk_get_max_transfer()
for accessing a backend's block limits.

Signed-off-by: Eric Blake <address@hidden>
---
 include/sysemu/block-backend.h | 1 +
 block/block-backend.c          | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 830d873f24f..20f8bbbce37 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -176,6 +176,7 @@ bool blk_is_available(BlockBackend *blk);
 void blk_lock_medium(BlockBackend *blk, bool locked);
 void blk_eject(BlockBackend *blk, bool eject_flag);
 int blk_get_flags(BlockBackend *blk);
+uint32_t blk_get_request_alignment(BlockBackend *blk);
 uint32_t blk_get_max_transfer(BlockBackend *blk);
 int blk_get_max_iov(BlockBackend *blk);
 void blk_set_guest_block_size(BlockBackend *blk, int align);
diff --git a/block/block-backend.c b/block/block-backend.c
index f2f75a977d7..fb8c827d117 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1798,6 +1798,13 @@ int blk_get_flags(BlockBackend *blk)
     }
 }

+/* Returns the minimum request alignment, in bytes; guaranteed nonzero */
+uint32_t blk_get_request_alignment(BlockBackend *blk)
+{
+    BlockDriverState *bs = blk_bs(blk);
+    return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE;
+}
+
 /* Returns the maximum transfer length, in bytes; guaranteed nonzero */
 uint32_t blk_get_max_transfer(BlockBackend *blk)
 {
-- 
2.14.4