[Qemu-devel] [RFC 01/12] Add iov_writev to use writev to send iovec (also for files)

[Orit Wasserman <owasserm@redhat.com>]

We use writev because sendmsg can only be used on socket fds.

Signed-off-by: Orit Wasserman <owasserm@redhat.com>
---
 include/qemu/iov.h | 12 ++++++++++++
 util/iov.c         | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/include/qemu/iov.h b/include/qemu/iov.h
index 68d25f2..e26b7ba 100644
--- a/include/qemu/iov.h
+++ b/include/qemu/iov.h
@@ -82,6 +82,18 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
 #define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
 
+/*
+ * writes iovcnt buffers of data described by iov to the file associated with
+ * the file descriptor fd.
+ *
+ * @fd - file descriptor
+ * @iov - iov to write
+ * @invcnt - number of buffers to write
+ *
+ * @return - number of bytes return or -1 on error
+ */
+ssize_t iov_writev(int fd, struct iovec *iov, unsigned iov_cnt);
+
 /**
  * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
  * in file `fp', prefixing each line with `prefix' and processing not more
diff --git a/util/iov.c b/util/iov.c
index 9dae318..bcd6e97 100644
--- a/util/iov.c
+++ b/util/iov.c
@@ -197,6 +197,42 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
     return ret;
 }
 
+ssize_t iov_writev(int fd, struct iovec *iov, unsigned iov_cnt)
+{
+#if defined CONFIG_IOVEC && defined CONFIG_POSIX
+    ssize_t ret;
+
+    do {
+        ret = writev(fd, iov, iov_cnt);
+    } while (ret < 0 && errno == EINTR);
+
+    return ret;
+#else
+    /* else send piece-by-piece */
+    /*XXX Note: windows has WSASend() and WSARecv() */
+    unsigned i = 0;
+    ssize_t ret = 0;
+    while (i < iov_cnt) {
+        ssize_t r = send(fd, iov[i].iov_base, iov[i].iov_len, 0);
+        if (r > 0) {
+            ret += r;
+        } else if (!r) {
+            break;
+        } else if (errno == EINTR) {
+            continue;
+        } else {
+            /* else it is some "other" error,
+             * only return if there was no data processed. */
+            if (ret == 0) {
+                ret = -1;
+            }
+            break;
+        }
+        i++;
+    }
+    return ret;
+#endif
+}
 
 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
                  FILE *fp, const char *prefix, size_t limit)
-- 
1.7.11.7