[PATCH 1/3] iov: Add 'offset' parameter to iov_to_buf()

[Hannes Reinecke <hare@suse.de>]

Occasionally, the buffer needs to be placed at a offset within
the iovec when copying the buffer to the iovec.

Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 hw/virtio-net.c        |    2 +-
 hw/virtio-serial-bus.c |    2 +-
 iov.c                  |   23 ++++++++++++++---------
 iov.h                  |    2 +-
 4 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index 6997e02..a32cc01 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -657,7 +657,7 @@ static ssize_t virtio_net_receive(VLANClientState *nc, const uint8_t *buf, size_
 
         /* copy in packet.  ugh */
         len = iov_from_buf(sg, elem.in_num,
-                           buf + offset, size - offset);
+                           buf + offset, 0, size - offset);
         total += len;
         offset += len;
         /* If buffers can't be merged, at this point we
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index 7f6db7b..53c58d0 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -103,7 +103,7 @@ static size_t write_to_port(VirtIOSerialPort *port,
         }
 
         len = iov_from_buf(elem.in_sg, elem.in_num,
-                           buf + offset, size - offset);
+                           buf + offset, 0, size - offset);
         offset += len;
 
         virtqueue_push(vq, &elem, len);
diff --git a/iov.c b/iov.c
index 588cd04..9ead6ee 100644
--- a/iov.c
+++ b/iov.c
@@ -15,21 +15,26 @@
 #include "iov.h"
 
 size_t iov_from_buf(struct iovec *iov, unsigned int iovcnt,
-                    const void *buf, size_t size)
+                    const void *buf, size_t offset, size_t size)
 {
-    size_t offset;
+    size_t iov_off, buf_off;
     unsigned int i;
 
-    offset = 0;
-    for (i = 0; offset < size && i < iovcnt; i++) {
-        size_t len;
+    iov_off = 0;
+    buf_off = 0;
+    for (i = 0; i < iovcnt && size; i++) {
+        if (offset < (iov_off + iov[i].iov_len)) {
+            size_t len = MIN((iov_off + iov[i].iov_len) - offset, size);
 
-        len = MIN(iov[i].iov_len, size - offset);
+            memcpy(iov[i].iov_base + (offset - iov_off), buf + buf_off, len);
 
-        memcpy(iov[i].iov_base, buf + offset, len);
-        offset += len;
+            buf_off += len;
+            offset += len;
+            size -= len;
+        }
+        iov_off += iov[i].iov_len;
     }
-    return offset;
+    return buf_off;
 }
 
 size_t iov_to_buf(const struct iovec *iov, const unsigned int iovcnt,
diff --git a/iov.h b/iov.h
index 60a8547..2677527 100644
--- a/iov.h
+++ b/iov.h
@@ -13,7 +13,7 @@
 #include "qemu-common.h"
 
 size_t iov_from_buf(struct iovec *iov, unsigned int iovcnt,
-                    const void *buf, size_t size);
+                    const void *buf, size_t offset, size_t size);
 size_t iov_to_buf(const struct iovec *iov, const unsigned int iovcnt,
                   void *buf, size_t offset, size_t size);
 size_t iov_size(const struct iovec *iov, const unsigned int iovcnt);
-- 
1.6.0.2