[oe] invalidating udev cache, how?
Koen Kooi
k.kooi at student.utwente.nl
Thu Dec 4 16:05:58 UTC 2008
Hi,
The udev 124 has cache (/etc/dev.tar) to avoid doing the coldplug udev
dance that can take a few seconds to a minute depending on machine speed
and kernel options. It is working a bit too well at the moment:
* user boots image with 2.6.26 kernel on an omap board
* user gets /dev/fb0
* user fixes the bootargs in uboot to enable the overlay
* user doesn't get /dev/fb1
so remove /etc/dev.tar and reboot: /dev/fb1 appears.
I also encountered a case where the permissions on /dev/null where wrong
during first boot (it's a mystery why that happened) and udev cached
those making ssh daemons fail on boot.
My current ideas:
1) remove /etc/dev.tar if its > x weeks old
2) recreate it on shutdown
3) remove it after x times
option 1) breaks on systems without an RTC and/or no /etc/timestamp
option 2) moves the slowness to shutdown
option 3) requires extra logic and filesystem access
and all options don't fix the first case I mentioned, they all take a
while to make /dev/fb1 appear.
The key is that it should be transparent to users, so adding a check for
.e.g 'ignore_dev.tar=1' in bootargs wouldn't work, since that implies
that users are aware of the problem and know how to 'fix' it.
Does anyone have other ways to invalidate the cache, and if not, which
option would get your vote?
regards,
Koen
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