5 files changed, 23 insertions, 1 deletions

diff --git a/block.c b/block.c
index 7904098..e293907 100644
--- a/block.c
+++ b/block.c
@@ -113,6 +113,16 @@ size_t bdrv_opt_mem_align(BlockDriverState *bs)
     return bs->bl.opt_mem_alignment;
 }
 
+size_t bdrv_min_mem_align(BlockDriverState *bs)
+{
+    if (!bs || !bs->drv) {
+        /* 4k should be on the safe side */
+        return 4096;
+    }
+
+    return bs->bl.min_mem_alignment;
+}
+
 /* check if the path starts with "<protocol>:" */
 int path_has_protocol(const char *path)
 {
@@ -890,6 +900,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
     }
 
     assert(bdrv_opt_mem_align(bs) != 0);
+    assert(bdrv_min_mem_align(bs) != 0);
     assert((bs->request_alignment != 0) || bs->sg);
     return 0;
 
diff --git a/block/io.c b/block/io.c
index a05ad67..e6c3639 100644
--- a/block/io.c
+++ b/block/io.c
@@ -201,8 +201,10 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
         }
         bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
         bs->bl.max_transfer_length = bs->file->bl.max_transfer_length;
+        bs->bl.min_mem_alignment = bs->file->bl.min_mem_alignment;
         bs->bl.opt_mem_alignment = bs->file->bl.opt_mem_alignment;
     } else {
+        bs->bl.min_mem_alignment = 512;
         bs->bl.opt_mem_alignment = 512;
     }
 
@@ -221,6 +223,9 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
         bs->bl.opt_mem_alignment =
             MAX(bs->bl.opt_mem_alignment,
                 bs->backing_hd->bl.opt_mem_alignment);
+        bs->bl.min_mem_alignment =
+            MAX(bs->bl.min_mem_alignment,
+                bs->backing_hd->bl.min_mem_alignment);
     }
 
     /* Then let the driver override it */
@@ -2489,7 +2494,7 @@ void *qemu_try_blockalign0(BlockDriverState *bs, size_t size)
 bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov)
 {
     int i;
-    size_t alignment = bdrv_opt_mem_align(bs);
+    size_t alignment = bdrv_min_mem_align(bs);
 
     for (i = 0; i < qiov->niov; i++) {
         if ((uintptr_t) qiov->iov[i].iov_base % alignment) {
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 24d8582..7083924 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -725,6 +725,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
     BDRVRawState *s = bs->opaque;
 
     raw_probe_alignment(bs, s->fd, errp);
+    bs->bl.min_mem_alignment = s->buf_align;
     bs->bl.opt_mem_alignment = s->buf_align;
 }
 
diff --git a/include/block/block.h b/include/block/block.h
index 7d1a717..c1c963e 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -440,6 +440,8 @@ void bdrv_img_create(const char *filename, const char *fmt,
 
 /* Returns the alignment in bytes that is required so that no bounce buffer
  * is required throughout the stack */
+size_t bdrv_min_mem_align(BlockDriverState *bs);
+/* Returns optimal alignment in bytes for bounce buffer */
 size_t bdrv_opt_mem_align(BlockDriverState *bs);
 void bdrv_set_guest_block_size(BlockDriverState *bs, int align);
 void *qemu_blockalign(BlockDriverState *bs, size_t size);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index db29b74..f004378 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -313,6 +313,9 @@ typedef struct BlockLimits {
     int max_transfer_length;
 
     /* memory alignment so that no bounce buffer is needed */
+    size_t min_mem_alignment;
+
+    /* memory alignment for bounce buffer */
     size_t opt_mem_alignment;
 } BlockLimits;