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iov: handle partial writes from sendmsg and recvmsg

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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>
This commit is contained in:
Paolo Bonzini 2013-03-27 17:36:31 +01:00
parent f48869ad28
commit 83f75c26e8
1 changed files with 57 additions and 49 deletions
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106
util/iov.c
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@ -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;
}
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;
}
/* 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);
/* 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;
}
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;
}
return ret;
return total;
}