Date: Wed, 7 Nov 2018 08:06:48 -0800 (PST) From: "Rodney W. Grimes" <freebsd@pdx.rh.CN85.dnsmgr.net> To: Ian Lepore <ian@freebsd.org> Cc: rgrimes@freebsd.org, Maxim Sobolev <sobomax@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org> Subject: Re: svn commit: r340187 - head/sys/geom Message-ID: <201811071606.wA7G6mQW001639@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <1541606248.52306.42.camel@freebsd.org>
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> On Tue, 2018-11-06 at 16:17 -0800, Rodney W. Grimes wrote:
> > >
> > > Rodney, this was actually my original intention, however then I noticed in
> > > the GEOM code there is at least one case when BIO_FLUSH request is being
> > > generated internally with bio_offset == mediasize and bio_lenth == 0, so I
> > > thought there might be some need to allow such requests through. But I'd
> > > happily go with the stricter rule if it does no harm. I simply don't know
> > > enough about the intended use and the logic behind zero-length transfers to
> > > make that call.
> > I am not sure enough on if mediasize is 0 based or not,
> > if it is then the error case should be fixed, and the
> > code you show below should also be fixed as it is
> > technically making a request beyond the end of device.
> >
> > I am also murky on why we are even doing a 0 size
> > operation and end of device, is that to validate
> > we can access all the media???If so then this wrong
> > code and wrong error return should be fixed as it
> > is off by 1.
> >
> > >
> > >
> > > -Max
> > >
> > > int
> > > g_io_flush(struct g_consumer *cp)
> > > {
> > > ...
> > > ????????bp = g_alloc_bio();
> > > ????????bp->bio_cmd = BIO_FLUSH;
> > > ...
> > > ????????bp->bio_offset = cp->provider->mediasize;
> > The above should have a - 1 on it.
> >
>
> Unless offset > mediasize is specifically a signal to downstream code
> in some way about how the flush is to be performed.
Could very well be, should be documented some place though.
> Nearly identical code to create a BIO_FLUSH bio appears in ufs softdeps
> and in zfs. Before starting to arbitrarily change code that has worked
> since 2006, it might be a good idea to track down why these values are
> set the way they are. Unfortunately, there is no clue in the commit
> logs, but maybe the author (pjd@, cc'd) can englighten us.
I agree with that take on the situation, and it is why I asked
for a revert and investigation, rather than trying to solve
why we suddenly fail some regression tests.
--
Rod Grimes rgrimes@freebsd.org
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