Re: [PATCH 2/2] qemu/osdep: handle sysconf(_SC_OPEN_MAX) return value == -1

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

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 <berrange@redhat.com>
>>> Signed-off-by: Clément Léger <cleger@rivosinc.com>
>>
>> Reviewed-by: Michael Tokarev <mjt@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.

>>> +#else
>>> +        open_max = 1024;
>>> +#endif
>>
>> BTW, Can we PLEASE cap this to 1024 in all cases? :)
>> (unrelated to this change but still).
> 
> Hi Michael,
> 
> Do you mean for all OSes or always using 1024 rather than using the
> sysconf returned value ?

Alternatively add:

   long qemu_sysconf(int name, long unsupported_default);

which returns value, unsupported_default if not supported, or -1.

> 
> In any case, the code now uses close_range() or /proc/self/fd and is
> handling that efficiently.
> 
> Thanks,
> 
> Clément
> 
>>
>> /mjt
> 
>