Date: Sun, 10 Oct 2021 07:48:49 -0600 From: Alan Somers <asomers@freebsd.org> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: RFC: Use of VOP_ALLOCATE() by NFSV4.2 nfsd Message-ID: <CAOtMX2j0gM-ujuK2G-%2Bzi9_eNtECy3CNv-ujZtajWgr3gvPMrg@mail.gmail.com> In-Reply-To: <YQXPR0101MB0968AE9C289D46AC37D48556DDB49@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> References: <YQXPR0101MB0968322C2DEBFAA672FFBC8EDDB49@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <CAOtMX2hyoyLam%2BOY7_hziiX7%2BEP8h2Ca4qiTpkj8suKZnkv68g@mail.gmail.com> <YQXPR0101MB0968AE9C289D46AC37D48556DDB49@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM>
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On Sat, Oct 9, 2021 at 11:57 PM Rick Macklem <rmacklem@uoguelph.ca> wrote: > > Alan Somers wrote: > >On Sat, Oct 9, 2021 at 7:13 PM Rick Macklem <rmacklem@uoguelph.ca> wrote: > >> > >> Hi, > >> > >> I ran into an issue this week during the nfsv4@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? No. It works for UFS, which is an overwriting file system. But for ZFS, when the user comes back later to rewrite those same offsets, ZFS will actually allocate new LBAs for them. > > >> - 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 > >
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