Re: [PATCH] Re: zero-filed page on VOP_PUTPAGES

[manu%netbsd.org@localhost (Emmanuel Dreyfus)]

YAMAMOTO Takashi <yamt%mwd.biglobe.ne.jp@localhost> wrote:

> > +                       rvap->va_size = MAX(rvap->va_size, vp->v_size);
> 
> couldn't it be a problem if the size of the file is shrinked by the server?

In that case, ou client will not see the file being shrunk until it
forgets about it and looks it up again. I guess it means that when you
hold a file open, you do not see it being shrunk by another client. 

That may be annoying, though I have trouble to find a situation where it
would cause problems. A mail system, perhaps, with clients being SMTP
and IMAP daemons? But in such a setup, you use locking so that only a
single client opens a mailbox, otherwise you breaak everything.

> how about stopping using FAF for SETATTR?
> i guess puffs_msg_setcall can be used instead.

I am not sure it would fix all corner cases. Basically the problem is
that synchronisation of kernel and filesystem view of file size are not
atomic. Getting rid of the FAF for SETATTR will not prevent a race with
another thread that tests or sets file size. 

-- 
Emmanuel Dreyfus
http://hcpnet.free.fr/pubz
manu%netbsd.org@localhost