block: Make blk_{pread,pwrite}() return 0 on success

They currently return the value of their 'bytes' parameter on success.

Make them return 0 instead, for consistency with other I/O functions and
in preparation to implement them using generated_co_wrapper. This also
makes it clear that short reads/writes are not possible.

Signed-off-by: Alberto Faria <afaria@redhat.com>
Message-Id: <20220705161527.1054072-2-afaria@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

2 files changed, 5 insertions, 8 deletions

diff --git a/block/block-backend.c b/block/block-backend.c
index f425b00793..4c5e130615 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1573,19 +1573,16 @@ int blk_pread(BlockBackend *blk, int64_t offset, void *buf, int bytes)
     ret = blk_do_preadv(blk, offset, bytes, &qiov, 0);
     blk_dec_in_flight(blk);
 
-    return ret < 0 ? ret : bytes;
+    return ret;
 }
 
 int blk_pwrite(BlockBackend *blk, int64_t offset, const void *buf, int bytes,
                BdrvRequestFlags flags)
 {
-    int ret;
     QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, buf, bytes);
     IO_OR_GS_CODE();
 
-    ret = blk_pwritev_part(blk, offset, bytes, &qiov, 0, flags);
-
-    return ret < 0 ? ret : bytes;
+    return blk_pwritev_part(blk, offset, bytes, &qiov, 0, flags);
 }
 
 int64_t blk_getlength(BlockBackend *blk)
diff --git a/block/qcow.c b/block/qcow.c
index c646d6b16d..25a43353c1 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -891,14 +891,14 @@ static int coroutine_fn qcow_co_create(BlockdevCreateOptions *opts,
 
     /* write all the data */
     ret = blk_pwrite(qcow_blk, 0, &header, sizeof(header), 0);
-    if (ret != sizeof(header)) {
+    if (ret < 0) {
         goto exit;
     }
 
     if (qcow_opts->has_backing_file) {
         ret = blk_pwrite(qcow_blk, sizeof(header),
                          qcow_opts->backing_file, backing_filename_len, 0);
-        if (ret != backing_filename_len) {
+        if (ret < 0) {
             goto exit;
         }
     }
@@ -908,7 +908,7 @@ static int coroutine_fn qcow_co_create(BlockdevCreateOptions *opts,
          i++) {
         ret = blk_pwrite(qcow_blk, header_size + BDRV_SECTOR_SIZE * i,
                          tmp, BDRV_SECTOR_SIZE, 0);
-        if (ret != BDRV_SECTOR_SIZE) {
+        if (ret < 0) {
             g_free(tmp);
             goto exit;
         }