[Virtio-fs] [PATCH 4/4] virtiofsd: use fallocate(2) instead posix_fallocate(3)

[Dr. David Alan Gilbert]

* Miklos Szeredi (mszeredi at redhat.com) wrote:
> On Wed, Apr 17, 2019 at 4:05 PM Dr. David Alan Gilbert
> <dgilbert at redhat.com> wrote:
> >
> > * Miklos Szeredi (mszeredi at redhat.com) wrote:
> > > On Wed, Apr 17, 2019 at 3:18 PM Dr. David Alan Gilbert
> > > <dgilbert at redhat.com> wrote:
> > > >
> > > > * Liu Bo (bo.liu at linux.alibaba.com) wrote:
> > > > > From: Xiaoguang Wang <xiaoguang.wang at linux.alibaba.com>
> > > > >
> > > > > This is because posix_fallocate(3) does not support FALLOC_FL_KEEP_SIZE
> > > > > and FALLOC_FL_PUNCH_HOLE. Our underlying host filesystem is ext4 and
> > > > > ext4 supports FALLOC_FL_KEEP_SIZE and FALLOC_FL_PUNCH_HOLE well, so
> > > > > this change will be ok.
> > > > >
> > > > > Signed-off-by: Xiaoguang Wang <xiaoguang.wang at linux.alibaba.com>
> > > >
> > > >   We need to check what 'fuse' expects - is it defined what
> > > > fallocate features it has, and what the semantics are?
> > >
> > > The patch looks good to me.
> > >
> > > Fuse (the kernel part) supports FALLOC_FL_KEEP_SIZE and
> > > FALLOC_FL_PUNCH_HOLE, but returns EOPNOTSUPP for any other flag.
> > >
> > > Even if, at a later time, fuse starts supporting additional fallocate
> > > flags, then the passthrough implementation calling fallocate(2) should
> > > be fine.
> >
> > OK, so then I'll take this patch; would it make sense for it to be sent
> > to upstream fuse?
> 
> It would have to be wrapped in #ifdef HAVE_FALLOCATE to make it
> portable.   Otherwise I don't see why not.

OK, I'll take it for now.

Liu Bo: Can you make it portable please and post it upstream on the fuse
list?

Dave

> Thanks,
> Miklos
--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK