Re: posix_fallocate on ZFS

On Sat, Feb 10, 2018 at 12:43 PM, Ian Lepore <ian_at_freebsd.org> wrote:

> On Sat, 2018-02-10 at 11:24 -0700, Alan Somers wrote:
> > On Sat, Feb 10, 2018 at 10:28 AM, Willem Jan Withagen
> > wrote:
> >
> > >
> > > Hi,
> > >
> > > This has been disabled on ZFS since last November.
> > > And I do understand the rationale on this.
> > >
> > > BUT
> > >
> > > I've now upgraded some of my HEAD Ceph test systems and they now fail,
> > > since Ceph uses posix_fallocate() to allocate space for the
> > > FileStore-journal.
> > >
> > > Is there any expectation that this is going to fixed in any near
> future?
> > >
> > > --WjW
> > >
> > No.  It's fundamentally impossible to support posix_fallocate on a COW
> > filesystem like ZFS.  Ceph should be taught to ignore an EINVAL result,
> > since the system call is merely advisory.
> >
> > -Alan
>
> Unfortunately, posix documents that the function returns EINVAL only
> due to bad input parameters, so ignoring that seems like a bad idea.
>
> Wouldn't it be better if we returned EOPNOTSUP if that's the actual
> situation?  That could be safely ignored.
>

I'm afraid you are mistaken.  Posix _should've_ required EOPNOTSUP in this,
but it actually requires EINVAL.

http://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_fallocate.html