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Re: [PATCH] <sys/stat.h>: Use Linux kernel UAPI header if available and useful
On Jun 06 2019, Florian Weimer <fweimer@redhat.com> wrote:
> * Andreas Schwab:
>
>> On Jun 06 2019, Florian Weimer <fweimer@redhat.com> wrote:
>>
>>> diff --git a/sysdeps/unix/sysv/linux/statx.c b/sysdeps/unix/sysv/linux/statx.c
>>> index b99e30dc3e..5d634960a6 100644
>>> --- a/sysdeps/unix/sysv/linux/statx.c
>>> +++ b/sysdeps/unix/sysv/linux/statx.c
>>> @@ -21,6 +21,11 @@
>>>
>>> #include "statx_generic.c"
>>>
>>> +/* Ensure that the kernel headers have not changed the struct size.
>>> + If this ever happens, it may be necessary to introduce a new symbol
>>> + version. */
>>> +_Static_assert (sizeof (struct statx) == 256, "struct statx size changed");
>>
>> Why is that needed? Isn't the point of statx that only the known parts
>> are filled?
>
> There have been some discussions that future kernel versions might add
> additional fields to the struct, outside the padding. Userspace would
> request that by setting an additional flag.
And why is that a problem? Either the kernel knows about the flag and
happily fills the structure, or it will return an error.
Andreas.
--
Andreas Schwab, SUSE Labs, schwab@suse.de
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