[1/6] block: Introduce bdrv_preadv()

Commit Message

Kevin Wolf June 10, 2016, 4:05 p.m. UTC

We already have a byte-based bdrv_pwritev(), but the read counterpart
was still missing. This commit adds it.

Signed-off-by: Kevin Wolf <[e-mail]>
---
 block/io.c            | 20 +++++++++++++-------
 include/block/block.h |  1 +
 2 files changed, 14 insertions(+), 7 deletions(-)

Comments

Eric Blake June 10, 2016, 8:50 p.m. UTC | #1

On 06/10/2016 10:05 AM, Kevin Wolf wrote:
> We already have a byte-based bdrv_pwritev(), but the read counterpart
> was still missing. This commit adds it.
> 
> Signed-off-by: Kevin Wolf <[e-mail]>
> ---
>  block/io.c            | 20 +++++++++++++-------
>  include/block/block.h |  1 +
>  2 files changed, 14 insertions(+), 7 deletions(-)
> 

Worth adding a flags argument while at it? But bdrv_pwritev() lacks one,
so for symmetry reasons, I'm okay if you don't bother.

> +int bdrv_preadv(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
> +{
> +    int ret;
> +
> +    ret = bdrv_prwv_co(bs, offset, qiov, false, 0);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    return qiov->size;

This implies we never have a short read, it's an all-or-none error or
success.  Matches what we've done elsewhere, so I guess it's right.

Reviewed-by: Eric Blake <[e-mail]>

Patch

diff --git a/block/io.c b/block/io.c
index b3d6228..11510cf 100644
--- a/block/io.c
+++ b/block/io.c
@@ -700,6 +700,18 @@  int bdrv_make_zero(BlockDriverState *bs, BdrvRequestFlags flags)
     }
 }
 
+int bdrv_preadv(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
+{
+    int ret;
+
+    ret = bdrv_prwv_co(bs, offset, qiov, false, 0);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return qiov->size;
+}
+
 int bdrv_pread(BlockDriverState *bs, int64_t offset, void *buf, int bytes)
 {
     QEMUIOVector qiov;
@@ -707,19 +719,13 @@  int bdrv_pread(BlockDriverState *bs, int64_t offset, void *buf, int bytes)
         .iov_base = (void *)buf,
         .iov_len = bytes,
     };
-    int ret;
 
     if (bytes < 0) {
         return -EINVAL;
     }
 
     qemu_iovec_init_external(&qiov, &iov, 1);
-    ret = bdrv_prwv_co(bs, offset, &qiov, false, 0);
-    if (ret < 0) {
-        return ret;
-    }
-
-    return bytes;
+    return bdrv_preadv(bs, offset, &qiov);
 }
 
 int bdrv_pwritev(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
diff --git a/include/block/block.h b/include/block/block.h
index fb0078f..aca7f23 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -232,6 +232,7 @@  int bdrv_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
 int bdrv_make_zero(BlockDriverState *bs, BdrvRequestFlags flags);
 int bdrv_pread(BlockDriverState *bs, int64_t offset,
                void *buf, int count);
+int bdrv_preadv(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov);
 int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
                 const void *buf, int count);
 int bdrv_pwritev(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov);