Re: [PATCH v3 0/3] preadv & pwritev syscalls.

Ralf Baechle wrote:

On Mon, Dec 15, 2008 at 12:36:14PM +0100, Gerd Hoffmann wrote:

quoted

Next revision of the patch series, with the alignment issue fixed by
swapping the last two arguments as suggested by arch maintainers.

I've dropped the now-obsolete wrappers for mips.  Ralf, please
double-check.

It fixes the alignment issue but still won't work; on MIPS 32-bit userspace
will pass the 64-bit argument in two registers but the 64-bit kernel code
will assume it to be passed in a single registers.  It'd be ugly but passing
a pointer to a 64-bit argument would solve the issue; something like this:

sys_preadv(unsigned long fd, const struct iovec __user *vec,
                  unsigned long vlen, loff_t __user *pos);
compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
                  unsigned long vlen, loff_t __user *pos);

Suggestion from the s390 front was to explicitly pass high and low part
of pos as two arguments.  A bit ugly too, but should work fine as well
and it avoids the user pointer dereference.  What do you think about this?

sys_splice uses loff_t __user * arguments as well and that's why it's
doesn't need any compat wrapper.

Well, avoiding the compat wrapper altogether unfortunately isn't going
to work because struct iovec looks different in 32 and 64 bit.

I'm surprised this works for x86; does x86-64 code really expect 64-bit
arguments as 2 32-bit arguments?

Args are passed on the stack, not in registers.

Patch 1/3 looks like it's a bug fix and you may want to submit this
separate from the remainder of the series for 2.6.28?

Yep, it is a separate bugfix.  Spotted by Christoph while reviewing v1,
but there are no other dependencies to this patch series.

cheers,
  Gerd