On Tue, Sep 03, 2024 at 05:02:44PM +0200, Philippe Mathieu-Daudé wrote:
> On 3/9/24 15:37, Clément Léger wrote:
> > On 03/09/2024 15:34, Philippe Mathieu-Daudé wrote:
> > > On 3/9/24 09:53, Clément Léger wrote:
> > > > On 02/09/2024 21:38, Philippe Mathieu-Daudé wrote:
> > > > > On 30/8/24 13:57, Clément Léger wrote:
> > > > > > On 30/08/2024 13:31, Michael Tokarev wrote:
> > > > > > > 30.08.2024 14:14, Clément Léger wrote:
> > > > > > > > On some systems (MacOS for instance), sysconf(_SC_OPEN_MAX) can
> > > > > > > > return
> > > > > > > > -1. In that case we should fallback to using the OPEN_MAX
> > > > > > > > define.
> > > > > > > > According to "man sysconf", the OPEN_MAX define should be
> > > > > > > > present and
> > > > > > > > provided by either unistd.h and/or limits.h so include them for
> > > > > > > > that
> > > > > > > > purpose. For other OSes, just assume a maximum of 1024 files
> > > > > > > > descriptors
> > > > > > > > as a fallback.
> > > > > > > >
> > > > > > > > Fixes: 4ec5ebea078e ("qemu/osdep: Move close_all_open_fds() to
> > > > > > > > oslib-
> > > > > > > > posix")
> > > > > > > > Reported-by: Daniel P. Berrangé <berra...@redhat.com>
> > > > > > > > Signed-off-by: Clément Léger <cle...@rivosinc.com>
> > > > > > >
> > > > > > > Reviewed-by: Michael Tokarev <m...@tls.msk.ru>
> > > > > > >
> > > > > > > > @@ -928,6 +933,13 @@ static void
> > > > > > > > qemu_close_all_open_fd_fallback(const
> > > > > > > > int *skip, unsigned int nskip,
> > > > > > > > void qemu_close_all_open_fd(const int *skip, unsigned int
> > > > > > > > nskip)
> > > > > > > > {
> > > > > > > > int open_max = sysconf(_SC_OPEN_MAX);
> > > > > > > > + if (open_max == -1) {
> > > > > > > > +#ifdef CONFIG_DARWIN
> > > > > > > > + open_max = OPEN_MAX;
> > > > >
> > > > > Missing errno check.
> > > >
> > > > man sysconf states that:
> > > >
> > > > "On error, -1 is returned and errno is set to indicate the error (for
> > > > example, EINVAL, indicating that name is invalid)."
> > > >
> > > > So it seems checking for -1 is enough no ? Or were you thinking about
> > > > something else ?
> > >
> > > Mine (macOS 14.6) is:
> > >
> > > RETURN VALUES
> > > If the call to sysconf() is not successful, -1 is returned and
> > > errno is set appropriately. Otherwise, if the variable is
> > > associated with functionality that is not supported, -1 is
> > > returned and errno is not modified. Otherwise, the current
> > > variable value is returned.
> >
> > Which seems to imply the same than mine right ? -1 is always returned in
> > case of error and errno might or not be set. So checking for -1 seems
> > enough to check an error return.
>
> Yes but we can check for the unsupported case. Something like:
>
> long qemu_sysconf(int name, long unsupported_default)
> {
> int current_errno = errno;
> long retval;
>
> retval = sysconf(name);
> if (retval == -1) {
> if (errno == current_errno) {
> return unsupported_default;
> }
> perror("sysconf");
> return -1;
> }
> return retval;
> }
That looks uncessarily complicated, and IMHO makes it less
portable. eg consider macOS behaviour:
"if the variable is associated with functionality that is
not supported, -1 is returned and errno is not modified"
vs Linux documented behaviour:
"If name corresponds to a maximum or minimum limit, and
that limit is indeterminate, -1 is returned and errno
is not changed."
IMHO we should do what Clément already suggested and set a
default anytime retval == -1, and ignore errno. There is
no user benefit from turning errnos into a fatal error
via perror()
With regards,
Daniel
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