[Qemu-devel] [RFC PATCH 1/3] block: add bdrv_get_alignment, use it

[Paolo Bonzini <pbonzini@redhat.com>]

We cannot simply use the guest logical block size on the host; we need
to ask the protocol driver about the minimum required alignment.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block.c           |   26 ++++++++++++++++++++++++--
 block.h           |    1 +
 block/raw-posix.c |    3 ++-
 block_int.h       |    1 +
 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index d015887..aba92ad 100644
--- a/block.c
+++ b/block.c
@@ -476,7 +476,7 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
     bs->sg = 0;
     bs->open_flags = flags;
     bs->growable = 0;
-    bs->buffer_alignment = 512;
+    bs->buffer_alignment = 0;
 
     pstrcpy(bs->filename, sizeof(bs->filename), filename);
     bs->backing_file[0] = '\0';
@@ -1361,6 +1361,27 @@ int64_t bdrv_get_allocated_file_size(BlockDriverState *bs)
 }
 
 /**
+ * Required buffer alignment for a file or device. Return < 0 if error or unknown.
+ */
+int bdrv_get_alignment(BlockDriverState *bs)
+{
+    BlockDriver *drv = bs->drv;
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+    if (bs->buffer_alignment == 0) {
+        if (drv->bdrv_get_alignment) {
+            bs->buffer_alignment = drv->bdrv_get_alignment(bs);
+        } else if (bs->file) {
+            bs->buffer_alignment = bdrv_get_alignment(bs->file);
+        } else {
+            bs->buffer_alignment = BDRV_SECTOR_SIZE;
+        }
+    }
+    return bs->buffer_alignment;
+}
+
+/**
  * Length of a file in bytes. Return < 0 if error or unknown.
  */
 int64_t bdrv_getlength(BlockDriverState *bs)
@@ -3025,7 +3046,8 @@ void bdrv_set_buffer_alignment(BlockDriverState *bs, int align)
 
 void *qemu_blockalign(BlockDriverState *bs, size_t size)
 {
-    return qemu_memalign((bs && bs->buffer_alignment) ? bs->buffer_alignment : 512, size);
+    int alignment = bs ? bdrv_get_alignment(bs) : 512;
+    return qemu_memalign(alignment, size);
 }
 
 void bdrv_set_dirty_tracking(BlockDriverState *bs, int enable)
diff --git a/block.h b/block.h
index a826059..5fa632c 100644
--- a/block.h
+++ b/block.h
@@ -294,6 +294,7 @@ int bdrv_img_create(const char *filename, const char *fmt,
                     const char *base_filename, const char *base_fmt,
                     char *options, uint64_t img_size, int flags);
 
+int bdrv_get_alignment(BlockDriverState *bs);
 void bdrv_set_buffer_alignment(BlockDriverState *bs, int align);
 void *qemu_blockalign(BlockDriverState *bs, size_t size);
 
diff --git a/block/raw-posix.c b/block/raw-posix.c
index a3de373..3482fc8 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -301,10 +301,11 @@ static int raw_open(BlockDriverState *bs, const char *filename, int flags)
  */
 static int qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov)
 {
+    int alignment = bdrv_get_alignment(bs);
     int i;
 
     for (i = 0; i < qiov->niov; i++) {
-        if ((uintptr_t) qiov->iov[i].iov_base % bs->buffer_alignment) {
+        if ((uintptr_t) qiov->iov[i].iov_base % alignment) {
             return 0;
         }
     }
diff --git a/block_int.h b/block_int.h
index 77c0187..6caf063 100644
--- a/block_int.h
+++ b/block_int.h
@@ -113,6 +113,7 @@ struct BlockDriver {
 
     const char *protocol_name;
     int (*bdrv_truncate)(BlockDriverState *bs, int64_t offset);
+    int (*bdrv_get_alignment)(BlockDriverState *bs);
     int64_t (*bdrv_getlength)(BlockDriverState *bs);
     int64_t (*bdrv_get_allocated_file_size)(BlockDriverState *bs);
     int (*bdrv_write_compressed)(BlockDriverState *bs, int64_t sector_num,
-- 
1.7.7.1