Re: [PATCH] accept4 tests: fix specified flags

[Pino Toscano]

On Friday 09 October 2015 15:41:47 Pádraig Brady wrote:
> On 09/10/15 14:38, Pino Toscano wrote:
> > On Thursday 08 October 2015 15:46:42 Pádraig Brady wrote:
> >> On 08/10/15 13:47, Pino Toscano wrote:
> >>> Pass only SOCK_* flags to accept4, as they are the only documented
> >>> ones, and passing others may trigger EINVAL.
> >>> * tests/test-accept4.c: (main): Pass SOCK_CLOEXEC instead of
> >>> O_CLOEXEC | O_BINARY to accept4.
> >>> ---
> >>>  ChangeLog            | 7 +++++++
> >>>  tests/test-accept4.c | 4 ++--
> >>>  2 files changed, 9 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/ChangeLog b/ChangeLog
> >>> index 02d8bf8..3601eda 100644
> >>> --- a/ChangeLog
> >>> +++ b/ChangeLog
> >>> @@ -1,3 +1,10 @@
> >>> +2015-10-08  Pino Toscano  <address@hidden>
> >>> +
> >>> + Pass only SOCK_* flags to accept4, as they are the only documented
> >>> + ones, and passing others may trigger EINVAL.
> >>> + * tests/test-accept4.c: (main): Pass SOCK_CLOEXEC instead of
> >>> + O_CLOEXEC | O_BINARY to accept4.
> >>> +
> >>>  2015-10-06  Pavel Raiskup  <address@hidden>
> >>>  
> >>>   gnulib-tool: fix tests of 'extensions' module
> >>> diff --git a/tests/test-accept4.c b/tests/test-accept4.c
> >>> index b24af0b..b2e6fa8 100644
> >>> --- a/tests/test-accept4.c
> >>> +++ b/tests/test-accept4.c
> >>> @@ -43,7 +43,7 @@ main (void)
> >>>  
> >>>      errno = 0;
> >>>      ASSERT (accept4 (-1, (struct sockaddr *) &addr, &addrlen,
> >>> -                     O_CLOEXEC | O_BINARY)
> >>> +                     SOCK_CLOEXEC)
> >>>              == -1);
> >>>      ASSERT (errno == EBADF);
> >>>    }
> >>> @@ -54,7 +54,7 @@ main (void)
> >>>      close (99);
> >>>      errno = 0;
> >>>      ASSERT (accept4 (99, (struct sockaddr *) &addr, &addrlen,
> >>> -                     O_CLOEXEC | O_BINARY)
> >>> +                     SOCK_CLOEXEC)
> >>>              == -1);
> >>>      ASSERT (errno == EBADF);
> >>>    }
> >>
> >> That change looks good, though it also suggests that
> >> the implementation doesn't assume the availability of SOCK_CLOEXEC etc.
> >> I think we also may need the following included in your patch,
> >> to ensure the test compiles on all platforms, and that those
> >> constants are defined appropriately on all platforms?
> > 
> > The idea seems ok -- should I merge it with my patch, or can/should it
> > go as separate patch?
> > 
> >> diff --git a/lib/accept4.c b/lib/accept4.c
> >> index adf0989..992dfd0 100644
> >> --- a/lib/accept4.c
> >> +++ b/lib/accept4.c
> >> @@ -24,10 +24,6 @@
> >>  #include "binary-io.h"
> >>  #include "msvc-nothrow.h"
> >>
> >> -#ifndef SOCK_CLOEXEC
> >> -# define SOCK_CLOEXEC 0
> >> -#endif
> >> -
> >>  int
> >>  accept4 (int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags)
> >>  {
> >> diff --git a/lib/sys_socket.in.h b/lib/sys_socket.in.h
> >> index d29cc09..2d9df45 100644
> >> --- a/lib/sys_socket.in.h
> >> +++ b/lib/sys_socket.in.h
> >> @@ -654,10 +654,16 @@ _GL_WARN_ON_USE (shutdown, "shutdown is not always 
> >> POSIX compliant - "
> >>
> >>  #if @GNULIB_ACCEPT4@
> >>  /* Accept a connection on a socket, with specific opening flags.
> >> -   The flags are a bitmask, possibly including O_CLOEXEC (defined in 
> >> <fcntl.h>)
> >> -   and O_TEXT, O_BINARY (defined in "binary-io.h").
> >> +   The flags are a bitmask, possibly including SOCK_NONBLOCK,
> >> +   SOCK_CLOEXEC, and O_TEXT, O_BINARY (defined in "binary-io.h").
> >>     See also the Linux man page at
> >>     
> >> <http://www.kernel.org/doc/man-pages/online/pages/man2/accept4.2.html>.  */
> >> +# ifndef SOCK_CLOEXEC
> >> +#  define SOCK_CLOEXEC O_CLOEXEC
> >> +# endif
> >> +# ifndef SOCK_NONBLOCK
> >> +#  define SOCK_NONBLOCK O_NONBLOCK
> >> +# endif
> >>  # if @HAVE_ACCEPT4@
> >>  #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
> >>  #   define accept4 rpl_accept4
> > 
> > SOCK_CLOEXEC is used only in src/accept4.c, so that seems ok.
> > OTOH, SOCK_NONBLOCK is checked in tests/test-nonblocking.c, where it
> > would enable the code passing extra flags to the socket type; defining
> > could make that check failing in case the OS does not implement accept4
> > (and thus we are providing SOCK_*). What do you think?
> 
> Yes good point.
> 
> accept4() makes no sense without SOCK_CLOEXEC or SOCK_NONBLOCK,
> so my change to define make sense in that respect.
> Defining them to non zero will ensure for example EINVAL is
> returned for SOCK_NONBLOCK on platforms where we replace accept4()
> (though I suppose we could simulate that also).

True: if gnulib is providing accept4 to some platform which does not
provide it, then SOCK_CLOEXEC and SOCK_NONBLOCK ought to be provided
too, as they are part of the interface.

> However SOCK_CLOEXEC and SOCK_NONBLOCK may not be defined
> on platforms with select(), and we probably shouldn't define
> as user space may be doing:
> 
>   #ifdef SOCK_CLOEXEC
>     socket(..., SOCK_CLOEXEC);
>   #else
>     socket();
>     fcntl(..., FD_CLOEXEC);
>   #endif

One workaround to that, albeit local to gnulib, would be to define
something like GNULIB_DEFINED_SOCK_NONBLOCK, and adapt
tests/test-nonblocking.c to
# if defined(SOCK_NONBLOCK) && !defined(GNULIB_DEFINED_SOCK_NONBLOCK)
or, even better, add some configure check to test whether
socket(.., .. | SOCK_NONBLOCK) works.

However, the above would not work with 3rd party code doing that check;
one could think that such code may be broken already, as the underlying
kernel could not support those extra flags for socket.

> So let's forget my adjustment and instead I suggest
> merging this into your change:
> 
> diff --git a/doc/glibc-functions/accept4.texi 
> b/doc/glibc-functions/accept4.texi
> index 20386e9..b4114db 100644
> --- a/doc/glibc-functions/accept4.texi
> +++ b/doc/glibc-functions/accept4.texi
> @@ -16,4 +16,7 @@ programs that spawn child processes.
> 
>  Portability problems not fixed by Gnulib:
>  @itemize
> address@hidden
> +SOCK_CLOEXEC and SOCK_NONBLOCK may not be defined
> +as they're also significant to the socket() function.
>  @end itemize
> diff --git a/tests/test-accept4.c b/tests/test-accept4.c
> index b24af0b..5a29680 100644
> --- a/tests/test-accept4.c
> +++ b/tests/test-accept4.c
> @@ -31,6 +31,10 @@ SIGNATURE_CHECK (accept4, int, (int, struct sockaddr *, 
> socklen_t *, int));
> 
>  #include "macros.h"
> 
> +#ifndef SOCK_CLOEXEC
> +# define SOCK_CLOEXEC 0
> +#endif
> +

I was not unsure about this, but then I noticed we do the same also in
lib/accept4.c itself, so it will not make things worse (platforms
without accept4 and SOCK_* flags already have an accept4 implementation
which basically works like socket).

Should I merge the above bit in my patch? What about authorship of it?

Thanks,
-- 
Pino Toscano

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