Re: [PATCH v2] Add preadv and pwritev system calls.

Gerd Hoffmann
2008-12-12T15:49:05Z

Matthew Wilcox wrote:
>> +asmlinkage ssize_t sys_preadv(unsigned long fd, const struct iovec __user *vec,
>> + unsigned long vlen, loff_t pos)
>> +asmlinkage ssize_t sys_pwritev(unsigned long fd, const struct iovec __user *vec,
>> + unsigned long vlen, loff_t pos)
>
> Are these prototypes required? MIPS and PARISC will need wrappers to
> fix them if they are. These two architectures have an ABI which
> requires 64-bit arguments to be passed in aligned pairs of registers,
> but glibc doesn't know that (and given the existence of syscall(3),
> can't do much about it even if it knew), so some of the arguments end up
> in the wrong registers.
>
> Things will go much better if we can prototype these as:
>
> asmlinkage ssize_t sys_preadv(unsigned int fd,
> const struct iovec __user *vec,
> loff_t pos, unsigned long vlen);
> asmlinkage ssize_t sys_pwritev(unsigned int fd,
> const struct iovec __user *vec,
> loff_t pos, unsigned long vlen);

Hmm. It is the argument ordering used by NetBSD, thats why I used that
too. It certainly should be the application-visible ordering. We'll
have glibc between apps and kernel though, so I think we can reorder the
arguments at syscall level if that helps on these archs. Cc'ing Ulrich
Drepper for comments on that.

> By the way, why did you make 'fd' an unsigned long? The rest of the
> kernel uses unsigned int.

sys_{readv,writev} have unsigned long too, this is where I got it from.
Don't know what the reason for this is, it looks a bit odd indeed.

cheers,
Gerd