allow qemu_iovec_from_buffer() to specify offset from which to start copying

Similar to
 qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
                   int c, size_t bytes);
the new prototype is:
 qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
                     const void *buf, size_t bytes);

The processing starts at offset bytes within qiov.

This way, we may copy a bounce buffer directly to
a middle of qiov.

This is exactly the same function as iov_from_buf() from
iov.c, so use the existing implementation and rename it
to qemu_iovec_from_buf() to be shorter and to match the
utility function.

As with utility implementation, we now assert that the
offset is inside actual iovec.  Nothing changed for
current callers, because `offset' parameter is new.

While at it, stop using "bounce-qiov" in block/qcow2.c
and copy decrypted data directly from cluster_data
instead of recreating a temp qiov for doing that.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

1 files changed, 3 insertions, 13 deletions

diff --git a/cutils.c b/cutils.c
index 0ddf4c7d74..b4dd844644 100644
--- a/cutils.c
+++ b/cutils.c
@@ -245,20 +245,10 @@ void qemu_iovec_to_buffer(QEMUIOVector *qiov, void *buf)
     }
 }
 
-void qemu_iovec_from_buffer(QEMUIOVector *qiov, const void *buf, size_t count)
+size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
+                           const void *buf, size_t bytes)
 {
-    const uint8_t *p = (const uint8_t *)buf;
-    size_t copy;
-    int i;
-
-    for (i = 0; i < qiov->niov && count; ++i) {
-        copy = count;
-        if (copy > qiov->iov[i].iov_len)
-            copy = qiov->iov[i].iov_len;
-        memcpy(qiov->iov[i].iov_base, p, copy);
-        p     += copy;
-        count -= copy;
-    }
+    return iov_from_buf(qiov->iov, qiov->niov, offset, buf, bytes);
 }
 
 size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,