On 12 August 2012 06:29, Michael Tokarev <m...@tls.msk.ru> wrote: > On 12.08.2012 01:24, Peter Maydell wrote: >> POSIX allows sendmsg() and recvmsg() to fail EMSGSIZE if passed a zero >> msg.msg_iovlen (in particular the MacOS X implementation will do this). > >> Handle the case where iov_send_recv() is passed a zero byte count >> explicitly, to avoid accidentally depending on the OS to treat zero >> msg_iovlen as a no-op. > >> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> >> --- >> This is what was causing 'make check' to fail on MacOS X. >> The other option was to declare that a zero bytecount was illegal, I guess. > > I don't think sending/receiving zero bytes is a good idea in the > first place. Which test were failed on MacOS? Was it failing at > test-iov "random I/O"? > > I thought I ensured that the test does not call any i/o function > with zero "count" argument. Might be I was wrong, and in that > case THAT place should be fixed instead. > > Can you provide a bit more details please?
Sure. It fails in test-iov: #0 0x000000010000103a in do_send_recv (sockfd=4, iov=0x10060ffb0, iov_cnt=0, do_send=false) at iov.c:101 #1 0x0000000100001318 in iov_send_recv (sockfd=4, iov=0x10060ffb0, iov_cnt=3, offset=0, bytes=0, do_send=<value temporarily unavailable, due to optimizations>) at iov.c:179 #2 0x00000001000025c4 in test_io () at tests/test-iov.c:229 because the test does: for (i = 0; i <= sz; ++i) { for (j = i; j <= sz; ++j) { k = i; iov_memset(iov, niov, 0, 0xff, -1); do { s = g_test_rand_int_range(0, j - k + 1); r = iov_recv(sv[0], iov, niov, k, s); so on the first time round the loop i=0 so k=0 and we pass a zero bytes count to iov_recv. > The whole thing is actually interesting: this is indeed a system- > dependent corner case which should be handled in the code to make > the routine consistent. But how to fix this is an open question > I think. Your approach seems to be best, but we as well may > print a warning there... Since sendmsg()/recvmsg() do permit you to send nothing by having a non-zero length vector whose elements are all zero bytes long, making the zero length vector a no-op seemed to be the consistent approach. -- PMM