| Message ID | 1344720275-26744-1-git-send-email-peter.maydell@linaro.org |
|---|---|
| State | New |
| Headers | show |
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.maydell@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? 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... Thank you! /mjt > iov.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/iov.c b/iov.c > index b333061..60705c7 100644 > --- a/iov.c > +++ b/iov.c > @@ -146,6 +146,13 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, > { > ssize_t ret; > unsigned si, ei; /* start and end indexes */ > + 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, */
On 12 August 2012 06:29, Michael Tokarev <mjt@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.maydell@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
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.maydell@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. Acked-by: Michael Tokarev <mjt@tls.msk.ru> Kevin, does this fix the test-iov failure you're seeing on one of the build bots? Thank you! /mjt > iov.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/iov.c b/iov.c > index b333061..60705c7 100644 > --- a/iov.c > +++ b/iov.c > @@ -146,6 +146,13 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, > { > ssize_t ret; > unsigned si, ei; /* start and end indexes */ > + 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, */
Am 12.08.2012 12:32, schrieb Michael Tokarev: > 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.maydell@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. > > Acked-by: Michael Tokarev <mjt@tls.msk.ru> > > Kevin, does this fix the test-iov failure you're seeing on one of > the build bots? It's not on a build bot but on my test machine, but yes, this does fix it indeed. Thanks for looking into it, Peter! Kevin
On Sat, Aug 11, 2012 at 10:24:35PM +0100, 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.maydell@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. > > iov.c | 7 +++++++ > 1 file changed, 7 insertions(+) Thanks, applied to the trivial patches tree: https://github.com/stefanha/qemu/commits/trivial-patches Stefan
diff --git a/iov.c b/iov.c index b333061..60705c7 100644 --- a/iov.c +++ b/iov.c @@ -146,6 +146,13 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, { ssize_t ret; unsigned si, ei; /* start and end indexes */ + 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, */
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.maydell@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. iov.c | 7 +++++++ 1 file changed, 7 insertions(+)