Re: [gentoo-dev] Re: rfc: improve file system mounting and unmounting in OpenRC

[Ian Stakenvicius]

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On 05/08/15 10:01 AM, William Hubbs wrote:
> On Wed, Aug 05, 2015 at 04:50:40AM +0000, Duncan wrote:
>> Ian Stakenvicius posted on Tue, 04 Aug 2015 17:17:51 -0400 as
>> excerpted:
>>
>>> So what you are suggesting here now is that you want to (A)
>>> potentially break mounting with the need to externally manage
>>> mounts via services in openrc instead of just using /etc/fstab,
>>> and (B) also break services if something doesn't start, which
>>> is one of the reasons why you wanted to go through with this
>>> per-mount service in the first place.  My point is that no, we
>>> should keep localmount as succeeding even if one of the
>>> dependent services fails to mount, *just like it does right
>>> now*, *for the same reasons* as it succeeds on failure right
>>> now.
>>
>> +1
>>
>> IMO, localmount must continue to succeed /by/ /default/, even if
>> some mounts fail, because it's basically legacy, and must
>> maintain legacy behavior.  Turning it into a wrapper "internally"
>> is fine, but the overall localmount must still succeed, as too
>> much depends on that behavior as it is.
>
> Here's what I'm trying to deal with. Consider what happens if
> service a still has "need localmount" and service b has "need
> mount.foo".
>
> Mounting a file system twice causes failures the second time it is
> mounted, so I  either have to add special handling in the new
> mount script for file systems that are already mounted or come up
> with a way to make sure localmount runs after all instances of the
> new mount script.

Yes.  I sincerely hope this was always part of the plan???

If localmount is kept as a 'mount -a' then it won't remount anything
that's already been mounted, so nothing to worry about there.  If it's
a wrapper to the individual local mount.*'s then it just has to
depend() on them all via a need/want (so that they will be brought in
even if they aren't in the runlevel) and/or the mount.*'s need a
'before localmount' so that they're definitely started/attempted
first.  Am I missing something that makes this harder than it seems?


>
> The issue with making sure all mount scripts run before localmount
> would complicate things more for users because they would have to
> add the mount.foo symlinks to the appropriate runlevels (boot for
> local file systems and default for network ones).

Likely true as things stand now, which is why I expect major changes
would be needed in openrc internals to make it so this is not
necessary.  At minimum, "want" dependencies would need to be used so
that if mount.foo's don't exist they won't cause depend() failures.

(You thought this system was going to let you get away with -not-
using 'want' for mounting, didn't you?  :)

Of course this still doesn't handle how depend() sections will be
dynamically generated from /etc/fstab in the first place, nor how the
cache will be affected by this; so there's still lots of work to do to
sort that out.

>
> If I did add special handling to the mount script for an
> already-mounted file system, what should that be -- to ignore it or
> remount it? I'm tending toward remount.

Well you're already deciding to return success if the mount.foo
doesn't actually point to a real mount, so I don't see why this can't
be extended to return success if the filesystem is already mounted
too.  But either way, so long as it works.


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