Re: [Qemu-devel] [PATCH] compatfd.c: Don't pass NULL pointer to SYS_signalfd

[Peter Maydell]

On 14 October 2011 18:20, Stefan Weil <s...@weilnetz.de> wrote:
> Am 13.10.2011 19:45, schrieb Peter Maydell:
>>
>> Don't pass a NULL pointer in to SYS_signalfd in qemu_signalfd_available():
>> this isn't valid and Valgrind complains about it.
>>
>> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
>> ---
>> compatfd.c | 12 ++++++++++--
>> 1 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/compatfd.c b/compatfd.c
>> index 31654c6..02306a4 100644
>> --- a/compatfd.c
>> +++ b/compatfd.c
>> @@ -119,9 +119,17 @@ int qemu_signalfd(const sigset_t *mask)
>> bool qemu_signalfd_available(void)
>> {
>> #ifdef CONFIG_SIGNALFD
>> + sigset_t mask;
>> + int fd;
>> + bool ok;
>> + sigemptyset(&mask);
>> errno = 0;
>> - syscall(SYS_signalfd, -1, NULL, _NSIG / 8);
>> - return errno != ENOSYS;
>> + fd = syscall(SYS_signalfd, -1, &mask, _NSIG / 8);
>> + ok = (errno != ENOSYS);
>> + if (fd >= 0) {
>
> Maybe better: fd != -1

Style issue -- I prefer the >= 0; if you do a
'git grep -A2 open' you'll see that mostly the existing
codebase does 'is it less than zero or not' comparisons
for "did this thing returning an fd fail?" checks, rather
than 'is it equal to -1 or not'.

>> + close(fd);
>> + }
>> + return ok;
>> #else
>> return false;
>> #endif
>
> The variable 'ok' is not needed, simply returning
> errno != ENOSYS would work, too.

The call to close() might have trashed errno (although
admittedly the chances of close() returning ENOSYS are
rather low I think it's clearer to return the result
of checking the errno for the syscall we care about rather
than the one we don't).

-- PMM