From: Luca Ceresoli <luca@lucaceresoli.net>
To: buildroot@busybox.net
Subject: [Buildroot] [RFC 3/6] system: add mdev-only /dev management (without devtmpfs)
Date: Fri, 18 Sep 2015 18:37:16 +0200 [thread overview]
Message-ID: <55FC3DBC.1080800@lucaceresoli.net> (raw)
In-Reply-To: <87fv2fvp5m.fsf@dell.be.48ers.dk>
Dear Peter,
Peter Korsgaard wrote:
>>>>>> "Arnout" == Arnout Vandecappelle <arnout@mind.be> writes:
>
> Hi,
>
> > On 15-09-15 14:01, Peter Korsgaard wrote:
> >> Or alternatively, extend the S10mdev logic to detect that it need to
> >> create a tmpfs on /dev (by looking for devtmpfs in /proc/filesystems or
> >> detecting that /dev is RO) and have all the fixup there. That way it
> >> atleast doesn't add any more complications to the rest of Buildroot /
> >> users.
>
> > That's a great idea, because it actually simplifies the buildroot code (no
> > longer needed to force devtmpfs in the kernel when mdev is selected).
>
> > To detect, it's as simple as:
>
> > if [ "$(cut -d ' ' -f 2,3 /proc/mounts | sed -n '/^\/dev /s///p')" != devtmpfs ]
>
> Or simply 'grep -q devtmpfs /proc/filesystems'. It doesn't check if /dev
> is really a devtmpfs, but as we force DEVTMPFS_MOUNT=y (and the cpio
> init wrapper) that is probably good enough.
>
> For mdev, I think it makes more sense to check if /dev is writable, as
> that is the really what mdev requires (E.G. we could be in an initramfs
> on a <2.6.32 kernel or similar.
>
Theoretically correct, but having a dynamic /dev management on flash
storage seems a very bad idea.
In addition, i'm not sure I can write a good test to check whether it's
writable. [ -w /dev] does not consider if the filesystem is mounted
read-only. Checking if "/" has the "ro" option in /proc/mounts can be
done. But I'm not sure there are other possible configuration that make
/dev not writable for other reasons. SELinux maybe?
Mmh, overall I think the best idea is to base mdev either on devtmpfs
or on a generic tmpfs. It's more or less what Arnout's test does, except
it does not take into account the case where a tmpfs (but not devtmpfs)
is already mounted. But this should happen only if a user tweaks inittab
to do so.
--
Luca
next prev parent reply other threads:[~2015-09-18 16:37 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-08 21:28 [Buildroot] [RFC 0/6] mdev-only /dev management (without devtmpfs) Luca Ceresoli
2015-09-08 21:28 ` [Buildroot] [RFC 1/6] Move mounting /sys from fstab to inittab Luca Ceresoli
2015-09-09 9:12 ` Arnout Vandecappelle
2015-09-08 21:28 ` [Buildroot] [RFC 2/6] system: clarify /dev management using devtmpfs + {mdev, eudev} Luca Ceresoli
2015-09-09 9:40 ` Arnout Vandecappelle
2015-09-09 10:53 ` Luca Ceresoli
2015-09-09 10:54 ` Arnout Vandecappelle
2015-09-08 21:28 ` [Buildroot] [RFC 3/6] system: add mdev-only /dev management (without devtmpfs) Luca Ceresoli
2015-09-09 9:21 ` Arnout Vandecappelle
2015-09-09 12:29 ` Luca Ceresoli
2015-09-09 12:32 ` Arnout Vandecappelle
2015-09-09 13:54 ` Thomas Petazzoni
2015-09-14 13:47 ` Luca Ceresoli
2015-09-14 22:23 ` Arnout Vandecappelle
2015-09-15 22:35 ` Luca Ceresoli
2015-09-14 20:53 ` Peter Korsgaard
2015-09-14 21:34 ` Thomas Petazzoni
2015-09-14 21:38 ` Peter Korsgaard
2015-09-15 7:30 ` Thomas Petazzoni
2015-09-15 8:09 ` Peter Korsgaard
2015-09-15 9:41 ` Thomas Petazzoni
2015-09-15 12:01 ` Peter Korsgaard
2015-09-15 12:27 ` Arnout Vandecappelle
2015-09-15 12:32 ` Peter Korsgaard
2015-09-18 16:37 ` Luca Ceresoli [this message]
2015-09-15 13:03 ` Thomas Petazzoni
2015-09-15 13:14 ` Peter Korsgaard
2015-09-15 22:34 ` Luca Ceresoli
2015-10-01 9:36 ` Luca Ceresoli
2015-10-01 10:03 ` Peter Korsgaard
2015-09-15 22:31 ` Luca Ceresoli
2015-09-16 7:32 ` Peter Korsgaard
2015-09-18 15:47 ` Luca Ceresoli
2015-09-09 9:34 ` Arnout Vandecappelle
2015-09-09 11:23 ` Thomas Petazzoni
2015-09-09 11:29 ` Thomas Petazzoni
2015-09-09 20:33 ` Arnout Vandecappelle
2015-09-14 16:07 ` Luca Ceresoli
2015-09-14 16:05 ` Luca Ceresoli
2015-09-14 19:34 ` Thomas Petazzoni
2015-09-14 20:19 ` Arnout Vandecappelle
2015-09-15 22:07 ` Luca Ceresoli
2015-09-08 21:28 ` [Buildroot] [RFC 4/6] system: strip the initial /dev for mdev-only /dev management Luca Ceresoli
2015-09-08 21:28 ` [Buildroot] [RFC 5/6] docs/manual: document "Dynamic using mdev only" " Luca Ceresoli
2015-09-09 10:39 ` Arnout Vandecappelle
2015-09-08 21:28 ` [Buildroot] [RFC 6/6] **** DO NOT COMMIT THIS **** ugly stuff to test mdev-only " Luca Ceresoli
2015-09-09 9:26 ` [Buildroot] [RFC 0/6] mdev-only /dev management (without devtmpfs) Arnout Vandecappelle
2015-09-09 11:30 ` Thomas Petazzoni
2015-09-14 21:03 ` Peter Korsgaard
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