Re: [Qemu-devel] [RFC PATCH v4 3/4] raw-posix: Add full image preallocation option

[Hu Tao]

On Fri, Jan 17, 2014 at 04:56:42PM +0800, Stefan Hajnoczi wrote:
> On Fri, Dec 27, 2013 at 11:05:53AM +0800, Hu Tao wrote:
> > diff --git a/block/raw-posix.c b/block/raw-posix.c
> > index 6f6b8c1..a722d27 100644
> > --- a/block/raw-posix.c
> > +++ b/block/raw-posix.c
> > @@ -1160,17 +1160,52 @@ static int64_t 
> > raw_get_allocated_file_size(BlockDriverState *bs)
> >      return (int64_t)st.st_blocks * 512;
> >  }
> >  
> > +#ifdef __linux__
> > +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> > +{
> > +    int ret = -1;
> > +
> > +    ret = fallocate(fd, 0, offset, length);
> > +    if (ret < 0) {
> > +        ret = -errno;
> > +    }
> > +
> > +    /* fallback to posix_fallocate() if fallocate() is not supported */
> > +    if (ret == -ENOSYS || ret == -EOPNOTSUPP) {
> > +        ret = posix_fallocate(fd, offset, length);
> > +    }
> > +
> > +    return ret;
> > +}
> 
> Why is this Linux-specific #ifdef necessary?  glibc will try to use the
> fallocate(2) system call, if possible.

Fine. I'll drop this.