consolidate qemu_iovec_copy() and qemu_iovec_concat() and make them consistent

qemu_iovec_concat() is currently a wrapper for
qemu_iovec_copy(), use the former (with extra
"0" arg) in a few places where it is used.

Change skip argument of qemu_iovec_copy() from
uint64_t to size_t, since size of qiov itself
is size_t, so there's no way to skip larger
sizes.  Rename it to soffset, to make it clear
that the offset is applied to src.

Also change the only usage of uint64_t in
hw/9pfs/virtio-9p.c, in v9fs_init_qiov_from_pdu() -
all callers of it actually uses size_t too,
not uint64_t.

One added restriction: as for all other iovec-related
functions, soffset must point inside src.

Order of argumens is already good:
 qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
                   int c, size_t bytes)
vs:
 qemu_iovec_concat(QEMUIOVector *dst,
                   QEMUIOVector *src,
                   size_t soffset, size_t sbytes)
(note soffset is after _src_ not dst, since it applies to src;
for memset it applies to qiov).

Note that in many places where this function is used,
the previous call is qemu_iovec_reset(), which means
many callers actually want copy (replacing dst content),
not concat.  So we may want to add a wrapper like
qemu_iovec_copy() with the same arguments but which
calls qemu_iovec_reset() before _concat().

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

block.c

@@ -3101,13 +3101,13 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
             // Add the first request to the merged one. If the requests are
             // overlapping, drop the last sectors of the first request.
             size = (reqs[i].sector - reqs[outidx].sector) << 9;
-            qemu_iovec_concat(qiov, reqs[outidx].qiov, size);
+            qemu_iovec_concat(qiov, reqs[outidx].qiov, 0, size);
 
             // We should need to add any zeros between the two requests
             assert (reqs[i].sector <= oldreq_last);
 
             // Add the second request
-            qemu_iovec_concat(qiov, reqs[i].qiov, reqs[i].qiov->size);
+            qemu_iovec_concat(qiov, reqs[i].qiov, 0, reqs[i].qiov->size);
 
             reqs[outidx].nb_sectors = qiov->size >> 9;
             reqs[outidx].qiov = qiov;

block/qcow2.c

@@ -549,7 +549,7 @@ static coroutine_fn int qcow2_co_readv(BlockDriverState *bs, int64_t sector_num,
         index_in_cluster = sector_num & (s->cluster_sectors - 1);
 
         qemu_iovec_reset(&hd_qiov);
-        qemu_iovec_copy(&hd_qiov, qiov, bytes_done,
+        qemu_iovec_concat(&hd_qiov, qiov, bytes_done,
             cur_nr_sectors * 512);
 
         switch (ret) {
@@ -720,7 +720,7 @@ static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
         assert((cluster_offset & 511) == 0);
 
         qemu_iovec_reset(&hd_qiov);
-        qemu_iovec_copy(&hd_qiov, qiov, bytes_done,
+        qemu_iovec_concat(&hd_qiov, qiov, bytes_done,
             cur_nr_sectors * 512);
 
         if (s->crypt_method) {

block/qed.c

@@ -1131,7 +1131,7 @@ static void qed_aio_write_alloc(QEDAIOCB *acb, size_t len)
 
     acb->cur_nclusters = qed_bytes_to_clusters(s,
             qed_offset_into_cluster(s, acb->cur_pos) + len);
-    qemu_iovec_copy(&acb->cur_qiov, acb->qiov, acb->qiov_offset, len);
+    qemu_iovec_concat(&acb->cur_qiov, acb->qiov, acb->qiov_offset, len);
 
     if (acb->flags & QED_AIOCB_ZERO) {
         /* Skip ahead if the clusters are already zero */
@@ -1177,7 +1177,7 @@ static void qed_aio_write_inplace(QEDAIOCB *acb, uint64_t offset, size_t len)
 
     /* Calculate the I/O vector */
     acb->cur_cluster = offset;
-    qemu_iovec_copy(&acb->cur_qiov, acb->qiov, acb->qiov_offset, len);
+    qemu_iovec_concat(&acb->cur_qiov, acb->qiov, acb->qiov_offset, len);
 
     /* Do the actual write */
     qed_aio_write_main(acb, 0);
@@ -1247,7 +1247,7 @@ static void qed_aio_read_data(void *opaque, int ret,
         goto err;
     }
 
-    qemu_iovec_copy(&acb->cur_qiov, acb->qiov, acb->qiov_offset, len);
+    qemu_iovec_concat(&acb->cur_qiov, acb->qiov, acb->qiov_offset, len);
 
     /* Handle zero cluster and backing file reads */
     if (ret == QED_CLUSTER_ZERO) {

cutils.c

@@ -172,48 +172,34 @@ void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len)
 }
 
 /*
- * Copies iovecs from src to the end of dst. It starts copying after skipping
+ * Concatenates (partial) iovecs from src to the end of dst.
- * the given number of bytes in src and copies until src is completely copied
+ * It starts copying after skipping `soffset' bytes at the
- * or the total size of the copied iovec reaches size.The size of the last
+ * beginning of src and adds individual vectors from src to
- * copied iovec is changed in order to fit the specified total size if it isn't
+ * dst copies up to `sbytes' bytes total, or up to the end
- * a perfect fit already.
+ * of src if it comes first.  This way, it is okay to specify
+ * very large value for `sbytes' to indicate "up to the end
+ * of src".
+ * Only vector pointers are processed, not the actual data buffers.
  */
-void qemu_iovec_copy(QEMUIOVector *dst, QEMUIOVector *src, uint64_t skip,
+void qemu_iovec_concat(QEMUIOVector *dst,
-    size_t size)
+                       QEMUIOVector *src, size_t soffset, size_t sbytes)
 {
     int i;
     size_t done;
-    void *iov_base;
+    struct iovec *siov = src->iov;
-    uint64_t iov_len;
-
     assert(dst->nalloc != -1);
-
+    assert(src->size >= soffset);
-    done = 0;
+    for (i = 0, done = 0; done < sbytes && i < src->niov; i++) {
-    for (i = 0; (i < src->niov) && (done != size); i++) {
+        if (soffset < siov[i].iov_len) {
-        if (skip >= src->iov[i].iov_len) {
+            size_t len = MIN(siov[i].iov_len - soffset, sbytes - done);
-            /* Skip the whole iov */
+            qemu_iovec_add(dst, siov[i].iov_base + soffset, len);
-            skip -= src->iov[i].iov_len;
+            done += len;
-            continue;
+            soffset = 0;
         } else {
-            /* Skip only part (or nothing) of the iov */
+            soffset -= siov[i].iov_len;
-            iov_base = (uint8_t*) src->iov[i].iov_base + skip;
-            iov_len = src->iov[i].iov_len - skip;
-            skip = 0;
         }
-
-        if (done + iov_len > size) {
-            qemu_iovec_add(dst, iov_base, size - done);
-            break;
-        } else {
-            qemu_iovec_add(dst, iov_base, iov_len);
     }
-        done += iov_len;
+    /* return done; */
-    }
-}
-
-void qemu_iovec_concat(QEMUIOVector *dst, QEMUIOVector *src, size_t size)
-{
-    qemu_iovec_copy(dst, src, 0, size);
 }
 
 void qemu_iovec_destroy(QEMUIOVector *qiov)

hw/9pfs/virtio-9p.c

@@ -1648,7 +1648,7 @@ out:
  * with qemu_iovec_destroy().
  */
 static void v9fs_init_qiov_from_pdu(QEMUIOVector *qiov, V9fsPDU *pdu,
-                                    uint64_t skip, size_t size,
+                                    size_t skip, size_t size,
                                     bool is_write)
 {
     QEMUIOVector elem;
@@ -1665,7 +1665,7 @@ static void v9fs_init_qiov_from_pdu(QEMUIOVector *qiov, V9fsPDU *pdu,
 
     qemu_iovec_init_external(&elem, iov, niov);
     qemu_iovec_init(qiov, niov);
-    qemu_iovec_copy(qiov, &elem, skip, size);
+    qemu_iovec_concat(qiov, &elem, skip, size);
 }
 
 static void v9fs_read(void *opaque)
@@ -1715,7 +1715,7 @@ static void v9fs_read(void *opaque)
         qemu_iovec_init(&qiov, qiov_full.niov);
         do {
             qemu_iovec_reset(&qiov);
-            qemu_iovec_copy(&qiov, &qiov_full, count, qiov_full.size - count);
+            qemu_iovec_concat(&qiov, &qiov_full, count, qiov_full.size - count);
             if (0) {
                 print_sg(qiov.iov, qiov.niov);
             }
@@ -1970,7 +1970,7 @@ static void v9fs_write(void *opaque)
     qemu_iovec_init(&qiov, qiov_full.niov);
     do {
         qemu_iovec_reset(&qiov);
-        qemu_iovec_copy(&qiov, &qiov_full, total, qiov_full.size - total);
+        qemu_iovec_concat(&qiov, &qiov_full, total, qiov_full.size - total);
         if (0) {
             print_sg(qiov.iov, qiov.niov);
         }

qemu-common.h

@@ -340,9 +340,8 @@ typedef struct QEMUIOVector {
 void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint);
 void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov);
 void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
-void qemu_iovec_copy(QEMUIOVector *dst, QEMUIOVector *src, uint64_t skip,
+void qemu_iovec_concat(QEMUIOVector *dst,
-    size_t size);
+                       QEMUIOVector *src, size_t soffset, size_t sbytes);
-void qemu_iovec_concat(QEMUIOVector *dst, QEMUIOVector *src, size_t size);
 void qemu_iovec_destroy(QEMUIOVector *qiov);
 void qemu_iovec_reset(QEMUIOVector *qiov);
 void qemu_iovec_to_buffer(QEMUIOVector *qiov, void *buf);