Re: udev - that famouse obsolete %e option

["Alexander E. Patrakov" <patrakov@ums.usu.ru>]

VMiklos wrote:
> 2006/8/1, Kay Sievers <kay.sievers@vrfy.org>:
>> If you want to work on this, please start with one of the several
>> solutions to name optical drives persistently by writing udev rules. I'm
>> sure at some point we will include one of them in the udev tree.
> 
> here cames my first try:
> 
> http://frugalware.org/~vmiklos/patches/udev-096-optical_gen.diff
> 
> comments? :)

(I have not fully read that, but can still identify missing pieces)

The interaction with the boot scripts must be documented. The problem is
that udev rules that are needed to generate cdrom rules are triggered
when the root filesystem is read-only, and thus the generated rules
cannot be saved without additional efforts.

Debian works around this by saving the generated rules to /dev/shm and
copying them to /etc/udev/rules.d in a separate bootscript. LFS in the
past (until the Debian-based generator was completely dropped due to
cries of some people about too much automation, and because of mails
like
http://archives.linuxfromscratch.org/mail-archives/lfs-dev/2006-May/057166.html) 

did the following:

# /etc/udev/rules.d/81-cdrom.rules: Set CD-ROM permissions and get
device capabilities
ACTION="add", SUBSYSTEM="block", ENV{ID_TYPE}="cd",
IMPORT{program}="cdrom_id --export $tempnode", GROUP="cdrom"

# /etc/udev/rules.d/82-persistent-cd.rules: generated file
ACTION="add", SUBSYSTEM="block", BUS="ide", ID="0.1",
ENV{ID_CDROM}="1", SYMLINK+="cdrom", ENV{GENERATED}="1"

# /etc/udev/rules.d/83-cdrom-symlinks.rules: Determine CD drive capability.

ACTION!="add",          GOTO="cd_aliases_generator_end"
SUBSYSTEM!="block",     GOTO="cd_aliases_generator_end"
ENV{GENERATED}="?*",   GOTO="cd_aliases_generator_end"

# Fail the uevent if the autogenerated rules cannot be saved
ENV{ID_CDROM}="?*", PROGRAM="/bin/grep -c ' / [^[:space:]]* rw'
/proc/mounts",
RESULT!="2", RUN+="/bin/false", GOTO="cd_aliases_generator_end"

ENV{ID_CDROM}="?*", PROGRAM="write_cd_aliases", SYMLINK+="%c"

LABEL="cd_aliases_generator_end"

The idea is that the rule with grep fails the entire uevent when the
root filesystem is read-only. Udev will then add a symlink to the
relevant directory in sysfs to /dev/.udev/failed, and a separate
bootscript will retrigger all failed uevents again after mounting all
filesystems.

-- 
Alexander E. Patrakov


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