@@ -563,6 +563,105 @@ static void *read_reply(
return body;
}
+/*
+ * Wrapper around sendmsg() to resubmit on EINTR or short write. Returns
+ * @true if all data was transmitted, or @false with errno for an error.
+ * Note: May alter @iov in place on resubmit.
+ */
+static bool sendmsg_exact(int fd, struct iovec *iov, unsigned int nr)
+{
+ struct msghdr hdr = {
+ .msg_iov = iov,
+ .msg_iovlen = nr,
+ };
+
+ /* Sanity check first element isn't empty */
+ assert(iov->iov_len == sizeof(struct xsd_sockmsg));
+
+ while (hdr.msg_iovlen) {
+ ssize_t res = sendmsg(fd, &hdr, 0);
+
+ if (res < 0 && errno == EINTR)
+ continue;
+ if (res <= 0)
+ return false;
+
+ while (res) {
+ if (res >= hdr.msg_iov->iov_len) {
+ /* Skip full element. */
+ res -= hdr.msg_iov->iov_len;
+ hdr.msg_iovlen--;
+ hdr.msg_iov++;
+ continue;
+ }
+
+ /* Partial element, adjust base/len. */
+ hdr.msg_iov->iov_len -= res;
+ hdr.msg_iov->iov_base += res;
+ break;
+ }
+
+ while (hdr.msg_iov->iov_len == 0) {
+ /* Skip empty element. */
+ hdr.msg_iovlen--;
+ hdr.msg_iov++;
+ }
+ }
+
+ return true;
+}
+
+/*
+ * Wrapper around sendmsg() to resubmit on EINTR or short write. Returns
+ * @true if all data was transmitted, or @false with errno for an error.
+ * Note: May alter @iov in place on resubmit.
+ */
+static bool writev_exact(int fd, struct iovec *iov, unsigned int nr)
+{
+ /* Sanity check first element isn't empty */
+ assert(iov->iov_len == sizeof(struct xsd_sockmsg));
+
+ while (nr) {
+ ssize_t res = writev(fd, iov, nr);
+
+ if (res < 0 && errno == EINTR)
+ continue;
+ if (res <= 0)
+ return false;
+
+ while (res) {
+ if (res >= iov->iov_len) {
+ /* Skip full element. */
+ res -= iov->iov_len;
+ nr--;
+ iov++;
+ continue;
+ }
+
+ /* Partial element, adjust base/len. */
+ iov->iov_len -= res;
+ iov->iov_base += res;
+ break;
+ }
+
+ while (iov->iov_len == 0) {
+ /* Skip empty element. */
+ nr--;
+ iov++;
+ }
+ }
+
+ return true;
+}
+
+static bool write_request(struct xs_handle *h, struct iovec *iov, unsigned int nr)
+{
+ if (h->is_socket)
+ return sendmsg_exact(h->fd, iov, nr);
+ else
+ return writev_exact(h->fd, iov, nr);
+}
+
/*
* Send message to xenstore, get malloc'ed reply. NULL and set errno on error.
*
@@ -605,9 +704,8 @@ static void *xs_talkv(struct xs_handle *h,
mutex_lock(&h->request_mutex);
- for (i = 0; i < num_vecs; i++)
- if (!xs_write_all(h->fd, iovec[i].iov_base, iovec[i].iov_len))
- goto fail;
+ if (!write_request(h, iovec, num_vecs))
+ goto fail;
ret = read_reply(h, &reply_type, len);
if (!ret)
With the input data now conveniently arranged, use writev()/sendmsg() instead of decomposing it into write() calls. This causes all requests to be submitted with a single system call, rather than at least two. While in principle short writes can occur, the chances of it happening are slim given that most xenbus comms are only a handful of bytes. Nevertheless, provide {writev,sendmsg}_exact() wrappers which take care of resubmitting on EINTR or short write. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Anthony PERARD <anthony.perard@vates.tech> CC: Juergen Gross <jgross@suse.com> --- tools/libs/store/xs.c | 104 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 101 insertions(+), 3 deletions(-)