[Buildroot] [PATCH] wf111: Add mdev dependency

Floris Bos bos at je-eigen-domein.nl
Wed Aug 12 10:29:45 UTC 2015


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



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