posix_fallocate on ZFS

[Willem Jan Withagen]

On 10/02/2018 19:24, Alan Somers wrote:
> On Sat, Feb 10, 2018 at 10:28 AM, Willem Jan Withagen <wjw at digiware.nl 
> <mailto:wjw at digiware.nl>> 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.

Yup, that was what I'm going to do.
But then I would like to know how to annotate it.

And I guess that I'd get reactions submitting code to fix this, since 
the journal could run out of space.
So I'd beter know what is going on.

I seem to remember that on a pool level is is possible to reserve space 
whilest creating a filesystem? And then it could/should be fixed when 
building the disk-infra for an OSD.

--WjW