RFC: syscall(2), annotation

[walter harms <wharms-fPG8STNUNVg@public.gmane.org>]

Am 26.04.2017 17:53, schrieb Al Viro:
> On Wed, Apr 26, 2017 at 12:35:08PM +0100, David Howells wrote:
> 
>> AT_EMPTY_PATH wasn't there back in 2010.  I could eliminate the:
>>
>> 	statx(fd, NULL, 0, ...);
>>
>> option in favour of:
>>
>> 	statx(fd, "", AT_EMPTY_PATH, ...);
>>
>> Any thoughts either way, Al?
>>
>> It would seem that AT_EMPTY_PATH should be redundant, though, since you can
>> just set the pathname pointer to NULL.
> 
> NULL pathname pointer means an error for a lot of existing syscalls, so
> if you want to turn them into wrappers for ...at() ones at libc level,
> you'd need to do special-casing of NULL both kernel-side and in libc wrappers.
> 
> Requiring "" + AT_EMPTY_PATH means a single dereference of userland pointer.  
> OTOH, that's not a terrible burden...


perhaps this is something the manpage should mention ?
lately we had some changes in syscall:
Re: [PATCH] syscall(2): note parisc handling of aligned register pairs

I have no clue about NULL pointers in syscalls() but when we write that
"General: pathname" (i assume: char *) "NULLpointer mean an error for
existing syscalls".

This sounds right,




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