[gentoo-user] udev + incron wheel's remake : hal/dbus usefulness quest

A small email to sumarize some thoughts about udev, removable
storage and incron to make the job of hal and re-invent the wheel.

---- context (skipable) -----
there is ONE common thing where gnome is quicker than bash : mounting
an unknown usb stick.

For my own stuff, I already used labels and uuids for ages but for
stranger devices it's not possible.

So those are the steps I did thousands of times :
- grab root (the device can be sdc3 as sde1 so there is no specific fstab entry)
- [dmesg|tail to check the device name or bash completion]
- mount -o users,rw /dev/new_device_X /mnt/remusb
- ^D
- cd /mnt/remusb

So what I needed was to get my plugged devices automounted to have
quickly a terminal in the directory. (I use fluxbox without idesk or
whatever)

Here comes the solution I found :

---- configuration -----------

FSTAB : some lines of /etc/fstab

LABEL=docus	/home/ftp/pub/Docus	ext3		users,auto		0 0
UUID=0467-FFC1	/mnt/mp3		vfat		users,rw,noatime	0 0

UDEV : some lines of /etc/udev/rules.d/80-custom.rules

ACTION=="add", SUBSYSTEM=="block", ENV{ID_FS_LABEL}=="docus", "RUN+="/bin/mount -L docus"
ACTION=="add", SUBSYSTEM=="block", ENV{ID_FS_UUID}=="0467-FFC1", RUN+="/bin/mkdir -p /mnt/mp3", RUN+="/bin/mount -U 0467-FFC1"

Ok, so this UDEV rules only make KNOWN devices automounted (but
nothing for unknown devices)

I then needed to have unknown devices mounted into /mnt/remusb, so the
other devices are given a $ENV{} variable.

ACTION=="add", SUBSYSTEM=="block", ENV{ID_FS_LABEL}=="docus", RUN+="/bin/mount -L docus", ENV{custom_rules}="add"
ACTION=="add", SUBSYSTEM=="block", ENV{ID_FS_UUID}=="0467-FFC1", RUN+="/bin/mkdir -p /mnt/mp3", RUN+="/bin/mount -U 0467-FFC1", ENV{custom_rules}="add"
# so I can add :
ACTION=="add", SUBSYSTEM=="block", KERNEL=="sd[b-z][1-9]", ENV{custom_rules}=="", RUN="mkdir -p /mnt/remusb", RUN+="mount /dev/%k /mnt/remusb"

But as I have many more removable medias, I factorised the code and used
exclusively ENV{} like the following :

## definitions examples :
ACTION=="add", SUBSYSTEM=="block", ENV{ID_FS_LABEL}=="integral", ENV{mount_point}="integral", ENV{mount_cmd}="-L integral", ENV{custom_rules}="add"ACTION=="add", SUBSYSTEM=="block", ENV{ID_FS_LABEL}=="docus", ENV{mount_cmd}="-L docus", ENV{custom_rules}="add"

## actions :
ENV{custom_rules}=="add", ENV{mount_point}!="", RUN+="/bin/mkdir -p /mnt/$env{mount_point}"
ENV{custom_rules}=="add", ENV{mount_cmd}!="", RUN+="/bin/mount $env{mount_cmd}"

--------------------
Now I want to be notified !
2 solutions :
- the bad one, udev runs as root : who && su -l my_user && DISPLAY=:0 osd_cat "new
  device"
- another one, use a per-session user daemon (as I ignored the hal
  documentation I didn't even looked at dbus-launch or others hal
  "plugins").

I decided to be notified by a file creation : INCRON
UDEV has to create a file in a directory monitored by incron.
[The creation a file whose name gives some useful information monitored by a daemon
is a kind a replacement of a real bus messaging system]

So, in the udev rule for my mp3 player I add the following :
RUN+="/bin/mkdir /tmp/.incron.device/%k"
(in fact I added it as the last one of the "actions" part of the udev rules file)

For my user I create a incrontab like :
/tmp/.incron.device IN_CREATE,IN_DELETE /home/myuser/.automount-script.sh $@ $# $%
So it's now possible to control what to do as udev notify us by incron,
better, monitoring /proc/partitions or whatever is useless as udev passes the
device name to incron which forward it to the script.

Example of automount-script.sh :
if [[ $theevent =~ IN_CREATE ]]; then
	destdir=$(mount|sed -n "s;^/dev/$thedevice on \(.*\) type.*$;\1;p")
	urxvtc -cd $destdir
fi

In that way I have a terminal spawned in the mount point each time
a removable device is plugged.

I attached my fstab, udev rule, incrontab -l and custom script.

I would be curious to read some advices about this architecture.

I also have 2 questions :
- what's the way to have a incremental number for unknown devices like
  /mnt/remusb1 then /mnt/remusb2 instead of /mnt/remusb (within udev) ?
- where to put the creation of /tmp/.incron.device in the init scripts
  to be sure it will be created BEFORE incron starts (without having to
  create a new startup script) ?

Raph