posix_fallocate on ZFS
Ian Lepore
ian at freebsd.org
Sat Feb 10 19:43:31 UTC 2018
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.
-- Ian
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