On Sat, Oct 9, 2021, 11:58 PM Rick Macklem <rmack...@uoguelph.ca> wrote:
> Alan Somers wrote: > >On Sat, Oct 9, 2021 at 7:13 PM Rick Macklem <rmack...@uoguelph.ca> wrote: > >> > >> Hi, > >> > >> I ran into an issue this week during the nf...@ietf.org's testing > event. > >> UFS - supports VOP_ALLOCATE() by using vop_stdallocate(). > >> ZFS - just return EINVAL for VOP_ALLOCATE(). > >> > >> An NFSv4.2 server can either support Allocate or not, but it has to be > >> for all exported file systems. > > > >That seems like a protocol bug to me. Could this be fixed in a future > >NFS revision? > Who knows. I don't see any interest in a 4.3. 4.2 is extensible, but I > think > this is now "cast in stone". > > >> > >> This leads me to a couple of questions: > >> - Is there a good reason for not using vop_stdallocate() for ZFS? > > > >Yes. posix_fallocate is supposed to guarantee that subsequent writes > >to the file will not fail with ENOSPC. But ZFS, being a copy-on-write > >file system, cannot possibly guarantee that. See SVN r325320. > However, vop_stdallocate() just does VOP_WRITE()s to the area (with > bytes of data all zeros). Wouldn't that satisfy the criteria? > Since it is log based, that would make it worse. The blocks aren't instantly reclaimed when marked invalid. So you'd need storage for both and the 0d blocks could cause a resource shortage when the real writes come in. ZFS doesn't have a reservation system to reserve blocks in the log for a given file... Warner >> - Should I try and support both file system types via vop_stdallocate() > >> or not support Allocate at all? > > > >Since you can't possibly support it for ZFS (not to mention other file > >systems like fusefs) you'll have to not support it at all. > It does sound like not supporting it is the best alternative. > > rick > > > > > Btw, as a bit of an aside, "cc" uses posix_fallocate() and in weird ways, > > such as offset=0, len=1. Why, I have no idea? > > > > Thanks in advance for any comments, rick > > > >