change qemu_iovec_to_buf() to match other to,from_buf functions

It now allows specifying offset within qiov to start from and
amount of bytes to copy.  Actual implementation is just a call
to iov_to_buf().
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

block.c

@@ -3408,7 +3408,7 @@ static BlockDriverAIOCB *bdrv_aio_rw_vector(BlockDriverState *bs,
     acb->bh = qemu_bh_new(bdrv_aio_bh_cb, acb);
 
     if (is_write) {
-        qemu_iovec_to_buffer(acb->qiov, acb->bounce);
+        qemu_iovec_to_buf(acb->qiov, 0, acb->bounce, qiov->size);
         acb->ret = bs->drv->bdrv_write(bs, sector_num, acb->bounce, nb_sectors);
     } else {
         acb->ret = bs->drv->bdrv_read(bs, sector_num, acb->bounce, nb_sectors);

block/iscsi.c

@@ -240,8 +240,7 @@ iscsi_aio_writev(BlockDriverState *bs, int64_t sector_num,
     /* this will allow us to get rid of 'buf' completely */
     size = nb_sectors * BDRV_SECTOR_SIZE;
     acb->buf = g_malloc(size);
-    qemu_iovec_to_buffer(acb->qiov, acb->buf);
-
+    qemu_iovec_to_buf(acb->qiov, 0, acb->buf, size);
 
     acb->task = malloc(sizeof(struct scsi_task));
     if (acb->task == NULL) {

block/qcow.c

@@ -569,7 +569,7 @@ static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,
 
     if (qiov->niov > 1) {
         buf = orig_buf = qemu_blockalign(bs, qiov->size);
-        qemu_iovec_to_buffer(qiov, buf);
+        qemu_iovec_to_buf(qiov, 0, buf, qiov->size);
     } else {
         orig_buf = NULL;
         buf = (uint8_t *)qiov->iov->iov_base;

block/qcow2.c

@@ -731,7 +731,7 @@ static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
 
             assert(hd_qiov.size <=
                    QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
-            qemu_iovec_to_buffer(&hd_qiov, cluster_data);
+            qemu_iovec_to_buf(&hd_qiov, 0, cluster_data, hd_qiov.size);
 
             qcow2_encrypt_sectors(s, sector_num, cluster_data,
                 cluster_data, cur_nr_sectors, 1, &s->aes_encrypt_key);

block/rbd.c

@@ -674,7 +674,7 @@ static BlockDriverAIOCB *rbd_start_aio(BlockDriverState *bs,
     acb->bh = NULL;
 
     if (cmd == RBD_AIO_WRITE) {
-        qemu_iovec_to_buffer(acb->qiov, acb->bounce);
+        qemu_iovec_to_buf(acb->qiov, 0, acb->bounce, qiov->size);
     }
 
     buf = acb->bounce;

cutils.c

@@ -220,15 +220,10 @@ void qemu_iovec_reset(QEMUIOVector *qiov)
     qiov->size = 0;
 }
 
-void qemu_iovec_to_buffer(QEMUIOVector *qiov, void *buf)
+size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
+                         void *buf, size_t bytes)
 {
-    uint8_t *p = (uint8_t *)buf;
-    int i;
-
-    for (i = 0; i < qiov->niov; ++i) {
-        memcpy(p, qiov->iov[i].iov_base, qiov->iov[i].iov_len);
-        p += qiov->iov[i].iov_len;
-    }
+    return iov_to_buf(qiov->iov, qiov->niov, offset, buf, bytes);
 }
 
 size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,

qemu-common.h

@@ -344,7 +344,8 @@ void qemu_iovec_concat(QEMUIOVector *dst,
                        QEMUIOVector *src, size_t soffset, size_t sbytes);
 void qemu_iovec_destroy(QEMUIOVector *qiov);
 void qemu_iovec_reset(QEMUIOVector *qiov);
-void qemu_iovec_to_buffer(QEMUIOVector *qiov, void *buf);
+size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
+                         void *buf, size_t bytes);
 size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
                            const void *buf, size_t bytes);
 size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,