Re: [Qemu-devel] [PATCH 6/6] experimental native preadv/pwritev support for Linux

[Christoph Hellwig <hch@lst.de>]

On Sun, Mar 15, 2009 at 04:36:16PM +0200, Blue Swirl wrote:
> On 3/14/09, Christoph Hellwig <hch@lst.de> wrote:
> >
> >
> >  This ties up Gerd Hoffmann's unmegred preadv/pwritev syscalls to qemu.  Use with
> >  care as the syscall numbers aren't finalized yet.
> >
> >  If someone of the BSD folks is interested it should be trivial to tie this up
> >  for the preadv/pwritev syscalls that have been around there for a while.
> 
> At least OpenBSD has preadv & pwritev.

NetBSD also.  But I don't have setup of either one, so I'll need some
help on that front.

> I'd add a check to configure to see if preadv exist and then define
> HAVE_PREADV. Though it's not possible to see if the kernel supports
> preadv if libc support does not exist (checking features by running
> programs breaks cross compilation).

The way glibc does it is only enable it if the underlying interface
exists, and then have another shortcut if it exists in the headers
but isn't supported by the underlying kernel.  That's what I'll try
to implement.