[Qemu-devel] [PATCH 2/3] NBD library: add aio-compatible read/write function

[Nicholas Thomas]

Signed-off-by: Nick Thomas <address@hidden>
---
 nbd.c |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 nbd.h |    2 ++
 2 files changed, 53 insertions(+), 0 deletions(-)

diff --git a/nbd.c b/nbd.c
index abe0ecb..83d3342 100644
--- a/nbd.c
+++ b/nbd.c
@@ -107,6 +107,57 @@ size_t nbd_wr_sync(int fd, void *buffer, size_t
size, bool do_read)
     return offset;
 }
 
+int nbd_wr_aio(int sockfd, struct iovec *iov, size_t len,  off_t
offset,
+               bool do_read)
+{
+    struct msghdr msg;
+    int ret, diff;
+
+    memset(&msg, 0, sizeof(msg));
+    msg.msg_iov = iov;
+    msg.msg_iovlen = 1;
+
+    len += offset;
+
+    while (iov->iov_len < len) {
+        len -= iov->iov_len;
+
+        iov++;
+        msg.msg_iovlen++;
+    }
+
+    diff = iov->iov_len - len;
+    iov->iov_len -= diff;
+
+    while (msg.msg_iov->iov_len <= offset) {
+        offset -= msg.msg_iov->iov_len;
+
+        msg.msg_iov++;
+        msg.msg_iovlen--;
+    }
+
+    msg.msg_iov->iov_base = (char *) msg.msg_iov->iov_base + offset;
+    msg.msg_iov->iov_len -= offset;
+
+retry:
+    if (do_read) {
+        ret = recvmsg(sockfd, &msg, 0);
+    } else {
+        ret = sendmsg(sockfd, &msg, 0);
+    }
+
+    /* recoverable error */
+    if (ret == -1 && (errno == EAGAIN || errno == EINTR)) {
+        goto retry;
+    }
+
+    msg.msg_iov->iov_base = (char *) msg.msg_iov->iov_base - offset;
+    msg.msg_iov->iov_len += offset;
+
+    iov->iov_len += diff;
+    return ret;
+}
+
 int tcp_socket_outgoing(const char *address, uint16_t port)
 {
     int s;
diff --git a/nbd.h b/nbd.h
index fc3a594..872218c 100644
--- a/nbd.h
+++ b/nbd.h
@@ -45,6 +45,8 @@ enum {
 #define NBD_DEFAULT_PORT       10809
 
 size_t nbd_wr_sync(int fd, void *buffer, size_t size, bool do_read);
+int nbd_wr_aio(int sockfd, struct iovec *iov, size_t len,  off_t
offset,
+               bool do_read);
 int tcp_socket_outgoing(const char *address, uint16_t port);
 int tcp_socket_incoming(const char *address, uint16_t port);
 int unix_socket_outgoing(const char *path);
-- 
1.7.0.4