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Date:      Sun, 8 Dec 2002 08:54:03 +1100 (EST)
From:      Bruce Evans <bde@zeta.org.au>
To:        Archie Cobbs <archie@dellroad.org>
Cc:        Kirk McKusick <mckusick@beastie.mckusick.com>, Julian Elischer <julian@elischer.org>, <freebsd-current@FreeBSD.ORG>, Thomas-Henning von Kamptz <tomsoft@FreeBSD.ORG>
Subject:   Re: backgroud fsck is still locking up system (fwd)
Message-ID:  <20021208083912.G14505-100000@gamplex.bde.org>
In-Reply-To: <200212072033.gB7KXddC072338@arch20m.dellroad.org>

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On Sat, 7 Dec 2002, Archie Cobbs wrote:

> Bruce Evans wrote:
> > Er, it should be obvious that growfs can't reasonably work on the mounted
> > partitions.  growfs.1 doesn't exist, but growfs.8 already has the warning
> > in a general form:
> >
> >      ....  Currently growfs can only enlarge unmounted file systems.  Do not
> >      try enlarging a mounted file system, your system may panic and you will
> >      not be able to use the file system any longer...
>
> Well, I suspected that it might not work... but I would disagree that it
> was *obvious* that it would not work. This was before "mount" had been
> run, so / was supposedly mounted (?) read-only.

Perhaps the unobvious point is that fsck could work.  If the mount is r/w,
then neither growfs nor fsck can even open the partition r/w.  fsck somehow
works in the case of a r/o root, but growfs apparently doesn't.  I think
fsck depends on no other processes making (significant) vfs syscalls for
on the same partition while it is running (even r/o ones might be harmful
if they caused reads of metadata which might be inconsistent).  Then when
fsck has finished it calls mount(... MNT_RELOAD...) to sync the metadata.
growfs doesn't do this, and even if it did it is not clear that it does
all the necessary syncing (growfs may change more or different metadata).
However, I think it does most of the necessary things.

Bruce


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