From: Floris Bos <bos@je-eigen-domein.nl>
To: buildroot@busybox.net
Subject: [Buildroot] [PATCH] wf111: Add mdev dependency
Date: Wed, 12 Aug 2015 12:29:45 +0200 [thread overview]
Message-ID: <55CB2019.5030304@je-eigen-domein.nl> (raw)
In-Reply-To: <1439277422-26111-1-git-send-email-cdhmanning@gmail.com>
On 08/11/2015 09:17 AM, Charles Manning wrote:
> wf111 really needs mdev
Problem I have seen with mdev in its default configuration is that it
doesn't just handle firmware load requests, but also takes it upon
itself to create/delete the device nodes (even when that already is
being handled by devtmpfs), and does a bad job with that.
It doesn't preserve sequencing by default, and events are processed
concurrently, and get out-of-order.
Becomes a problem if your software for example does anything that causes
the kernel to re-read the partition table of your storage.
In that case the kernel sends events to delete all devices nodes of the
storage device, and add them again, right after each other.
However depending on your luck, they can get processed in reverse order:
==
mdev[598]: 9.191594 ACTION:add SUBSYSTEM:block DEVNAME:mmcblk0p6
DEVPATH:/devices/platform/soc/3f300000.mmc/mmc_host/mmc0/mmc0:1234/block/mmcblk0/mmcblk0p6
mdev[598]: dev 179,6
[...]
mdev[593]: 9.192168 ACTION:remove SUBSYSTEM:block DEVNAME:mmcblk0p6
DEVPATH:/devices/platform/soc/3f300000.mmc/mmc_host/mmc0/mmc0:1234/block/mmcblk0/mmcblk0p6
mdev[593]: rule matched, line -1
mdev[593]: unlink: mmcblk0p6
==
Add is processed before remove, with the end result that /dev/mmcblk0p6
goes missing...
So please don't pull in mdev automatically just for firmware loading,
because it does more than just that, and can have serious side effects.
Yours sincerely,
Floris Bos
next prev parent reply other threads:[~2015-08-12 10:29 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-11 7:17 [Buildroot] [PATCH] wf111: Add mdev dependency Charles Manning
2015-08-11 11:40 ` Baruch Siach
2015-08-11 20:11 ` Charles Manning
2015-08-12 4:38 ` Baruch Siach
2015-08-12 5:16 ` Charles Manning
2015-08-12 5:38 ` Baruch Siach
2015-08-12 5:56 ` Charles Manning
2015-08-12 22:54 ` Floris Bos
2015-08-12 10:29 ` Floris Bos [this message]
2015-08-12 20:49 ` Charles Manning
2015-08-12 21:47 ` Floris Bos
2015-08-18 20:28 ` Thomas Petazzoni
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