Re: CVS commit: [yamt-nfs-mp] src/sys

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

hi,

> On Thu, Jun 25, 2009 at 12:47:38AM +0000, YAMAMOTO Takashi wrote:
>> > On Wed, Jun 24, 2009 at 02:21:44PM +0000, YAMAMOTO Takashi wrote:
>> >> Module Name:      src
>> >> Committed By:     yamt
>> >> Date:             Wed Jun 24 14:21:44 UTC 2009
>> >> 
>> >> Modified Files:
>> >>   src/sys/kern [yamt-nfs-mp]: vfs_syscalls.c
>> >>   src/sys/nfs [yamt-nfs-mp]: nfs_vfsops.c nfs_vnops.c
>> >> 
>> >> Log Message:
>> >> lock vnode when calling VOP_GETATTR because there's no reasonable way for
>> >> an implementation of VOP_GETATTR to prevent the vnode from being revoked.
>> > 
>> > I've not looked at the specific code, but surely a reference count is 
>> > enough?
>> > Requiring callers to lock vnodes doesn't seem right to me - since it
>> > is only likely to cause locking violations in layered fs.
>> > 
>> > The fact that the caller has a reference to the vnode at all should
>> > really be enough, surely??
>> 
>> do you mean vref?
>> it doesn't prevent revoke(2).
>> thus a filesystem can't access v_data safely.
> 
> How does Solaris do this? My understanding is you _don't_ have to lock 
> nodes any where near as often as we do (or did last I looked, which was 
> admittedly a while ago).
> 
> I think we should steal some other OSs vnode interface, at least as far as 
> locking and reclaim logic. Since we are turning into SolarisBSD (a good 
> thing!), it's a likely choice.
> 
> Other OSs have faced this issue and fixed it. Let's learn from them. :-)
> 
> Take care,
> 
> Bill

iirc,
        - solaris doesn't have revoke.  (i don't know what it does for
          forced unmount.)
        - freebsd removed the support of revoking non-device files.
        - dragonflybsd has some change in this area.

anyway, fixing revoke is not in the scope of this branch. :-)

YAMAMOTO Takashi