[8837] in athena10
Re: [Debathena] #463: Pay attention to the state of union mounts
daemon@ATHENA.MIT.EDU (Debathena Trac)
Thu Feb 23 15:11:40 2012
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From: "Debathena Trac" <debathena@MIT.EDU>
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To: geofft@MIT.EDU, broglek@MIT.EDU
Date: Thu, 23 Feb 2012 20:11:36 -0000
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#463: Pay attention to the state of union mounts and overlayfs
--------------------------+------------------------------------------------
Reporter: geofft | Owner:
Type: enhancement | Status: new
Priority: normal | Milestone: Precise Alpha
Component: login chroot | Resolution:
Keywords: | Upstream bug: http://valerieaurora.org/union/
--------------------------+------------------------------------------------
Comment (by geofft):
[http://thread.gmane.org/gmane.linux.file-systems/61698 v2 union mount
patches] were just posted; doesn't look like they're requesting a merge
into mainline though.
Also, regarding overlayfs' usability,
[http://irclogs.ubuntu.com/2012/02/16/%23ubuntu-devel.txt from #ubuntu-
devel]:
{{{
[02:00] <broder> oh what the heck. why does insserv ftbfs, but only in
sbuild
[02:00] <broder> ...with fopen(file_the_test_suite_just_wrote_out):
Operation not permitted
[02:00] <infinity> broder: In your local sbuild, you mean?
[02:00] <broder> infinity: yeah
[02:00] <infinity> broder: Is that running on top of an overlayfs-using
schroot?
[02:00] <infinity> broder: If so, that's your answer.
[02:00] <broder> ...seriously?
[02:01] <broder> ugh
[02:01] <infinity> broder: The good news is that the buildds won't fail
that way. :P
[02:01] <infinity> broder: The bad news is you need to test without
overlayfs locally.
[02:01] <broder> wait, but why does it not happen if i build it with
schroot dpkg-buildpackage, but not using sbuild?
[02:02] <broder> oh, i guess that would be hitting one of the bind mounts
[02:02] <broder> what is overlayfs doing wrong?
[02:02] <infinity> broder: overlayfs plays fast and loose with inodes in
ways that can confuse tools that assume that inodes don't (or do) change
based on certain actions.
[02:03] <broder> oww
[02:03] <infinity> broder: The tools (or, in this case, test suite) are
usually wrong, not overlayfs, but...
[02:04] <broder> ok. since i *can* build it without copying the source
into the overlayfs, i'll go ahead and move forward
[02:04] <geofft> infinity: out of curiosity, is there documentation of
usual overlayfs issues?
[02:04] <geofft> I have a local buildd that I was just about to switch
from LVM chroots to overlayfs one of these weekends...
[02:04] <infinity> geofft: Mostly in apw's head, and scattered around to
others who've had to deal with it. :P
[02:05] <infinity> geofft: If you have a working LVM setup, I see no
compelling reason to switch.
[02:05] <geofft> infinity: "working" is a bit much, it randomly panics
during rebuilds every so often
[02:05] <infinity> Special.
[02:06] <broder> also LVM snapshot-based chroots are borderline unusably
slow, especially when there are a lot of them in action
[02:08] <infinity> Anyhow, other than "some software makes stupid
assumptions about filesystems that it shouldn't" and "overlayfs doesn't
support inotify", I can't think of any other known gotchas.
}}}
and [http://irclogs.ubuntu.com/2012/02/22/%23ubuntu-devel.txt later]:
{{{
[01:53] <broder> a dpkg trigger wouldn't be an unreasonable way to work
around overlayfs+inotify sucking
[01:54] <SpamapS> GrueMaster: no build will work if it depends on an
upstart job AFAICT
[01:54] <SpamapS> broder: well in mk-sbuild chroots, policy.d denies
starting jobs anyway
[01:54] <broder> SpamapS: right, but there's a livecd issue
[01:54] <SpamapS> policy-rc.d rather.. or whatever its called
[01:55] <SpamapS> broder: I think we should actually be able to fix
overlayfs.. very troubling to me that its broken.
[01:55] * SpamapS wanders off to eat dinner.
[01:56] <broder> good plan :)
[02:09] <infinity> SpamapS: Fixing inotify in overlayfs is a much tougher
problem than it looks like at first blush. apw and I have talked circles
around it a few times.
}}}
So, we may want to wait out union mounts for actual logins as opposed to
just the buildd, sadly.
--
Ticket URL: <https://athena10.mit.edu/trac/ticket/463#comment:8>
Debathena <http://debathena.mit.edu>
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