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authorPaolo Bonzini <pbonzini@redhat.com>2013-03-27 17:36:31 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2013-04-17 11:43:45 +0200
commit83f75c26e8e791311900d0e2a4cc9379abedb85c (patch)
tree691a4afcbe0ca292576057bd5b67691301082db1 /util
parentf48869ad2825b640911666bb091cedb1e1d6ad5e (diff)
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iov: handle partial writes from sendmsg and recvmsg
Partial writes can still happen in sendmsg and recvmsg, if a signal is received in the middle of a write. To handle this, retry the operation with a new offset/bytes pair. Reviewed-by: Juan Quintela <quintela@redhat.com> Reviewed-by: Orit Wassermann <owasserm@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'util')
-rw-r--r--util/iov.c102
1 files changed, 55 insertions, 47 deletions
diff --git a/util/iov.c b/util/iov.c
index f14ff0b..d32226d 100644
--- a/util/iov.c
+++ b/util/iov.c
@@ -144,63 +144,71 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
size_t offset, size_t bytes,
bool do_send)
{
+ ssize_t total = 0;
ssize_t ret;
size_t orig_len, tail;
unsigned niov;
- if (bytes == 0) {
- /* Catch the do-nothing case early, as otherwise we will pass an
- * empty iovec to sendmsg/recvmsg(), and not all implementations
- * accept this.
- */
- return 0;
- }
-
- /* Find the start position, skipping `offset' bytes:
- * first, skip all full-sized vector elements, */
- for (niov = 0; niov < iov_cnt && offset >= iov[niov].iov_len; ++niov) {
- offset -= iov[niov].iov_len;
- }
+ while (bytes > 0) {
+ /* Find the start position, skipping `offset' bytes:
+ * first, skip all full-sized vector elements, */
+ for (niov = 0; niov < iov_cnt && offset >= iov[niov].iov_len; ++niov) {
+ offset -= iov[niov].iov_len;
+ }
- /* niov == iov_cnt would only be valid if bytes == 0, which
- * we already ruled out above. */
- assert(niov < iov_cnt);
- iov += niov;
- iov_cnt -= niov;
-
- if (offset) {
- /* second, skip `offset' bytes from the (now) first element,
- * undo it on exit */
- iov[0].iov_base += offset;
- iov[0].iov_len -= offset;
- }
- /* Find the end position skipping `bytes' bytes: */
- /* first, skip all full-sized elements */
- tail = bytes;
- for (niov = 0; niov < iov_cnt && iov[niov].iov_len <= tail; ++niov) {
- tail -= iov[niov].iov_len;
- }
- if (tail) {
- /* second, fixup the last element, and remember the original
- * length */
+ /* niov == iov_cnt would only be valid if bytes == 0, which
+ * we already ruled out in the loop condition. */
assert(niov < iov_cnt);
- assert(iov[niov].iov_len > tail);
- orig_len = iov[niov].iov_len;
- iov[niov++].iov_len = tail;
- }
+ iov += niov;
+ iov_cnt -= niov;
+
+ if (offset) {
+ /* second, skip `offset' bytes from the (now) first element,
+ * undo it on exit */
+ iov[0].iov_base += offset;
+ iov[0].iov_len -= offset;
+ }
+ /* Find the end position skipping `bytes' bytes: */
+ /* first, skip all full-sized elements */
+ tail = bytes;
+ for (niov = 0; niov < iov_cnt && iov[niov].iov_len <= tail; ++niov) {
+ tail -= iov[niov].iov_len;
+ }
+ if (tail) {
+ /* second, fixup the last element, and remember the original
+ * length */
+ assert(niov < iov_cnt);
+ assert(iov[niov].iov_len > tail);
+ orig_len = iov[niov].iov_len;
+ iov[niov++].iov_len = tail;
+ }
- ret = do_send_recv(sockfd, iov, niov, do_send);
+ ret = do_send_recv(sockfd, iov, niov, do_send);
- /* Undo the changes above */
- if (tail) {
- iov[niov-1].iov_len = orig_len;
- }
- if (offset) {
- iov[0].iov_base -= offset;
- iov[0].iov_len += offset;
+ /* Undo the changes above before checking for errors */
+ if (tail) {
+ iov[niov-1].iov_len = orig_len;
+ }
+ if (offset) {
+ iov[0].iov_base -= offset;
+ iov[0].iov_len += offset;
+ }
+
+ if (ret < 0) {
+ assert(errno != EINTR);
+ if (errno == EAGAIN && total > 0) {
+ return total;
+ }
+ return -1;
+ }
+
+ /* Prepare for the next iteration */
+ offset += ret;
+ total += ret;
+ bytes -= ret;
}
- return ret;
+ return total;
}