[arch-general] udev rules 2 times exec script

[Maarten de Vries]

On Sat, 12 Jun 2021 at 18:44, Maykel Franco via arch-general <
arch-general at lists.archlinux.org> wrote:

> El sáb, 12 jun 2021 a las 17:43, mpan via arch-general
> (<arch-general at lists.archlinux.org>) escribió:
> >
> >    If the command shares any resources, and name “autobackup” suggests
> > it does, it should include some mechanism that prevents concurrent
> > execution if another instance is already running. Otherwise, even if a
> > single match happens, multiple instances of the script may be executed.
> > For USB devices that may be a tiny power interruption during insertion,
> > causing it to be detected, removed, detected again:
> >
> > insertion - - - removal - - - insertion - - - - - - -
> >    |-- script ---------------------------------------> \_ two instances
> >                                  |-- script ---------> /  of the code
> >
> > It should be either of those:
> >    |-- script ------------------------------------------------->
> >                                  |--- BAIL OUT! -|
> > or
> >    |-- script --------------------------------- end|
> >                                  |-- WAIT .......... script --->
> >
> > > SUBSYSTEM=="block", ACTION=="add", ATTRS{idVendor}=="058f",
> > > ATTRS{idProduct}=="6387", SYMLINK+="external%n",
> > > RUN+="/usr/local/bin/autobackup.sh"
> > >
> > > This works well, buth exec 2 times the script...
> > >
> > > Jun 12 13:53:09 archlaptop autobackup.sh: BEGIN SCRIPT
> > > Jun 12 13:53:13 archlaptop autobackup.sh: BEGIN SCRIPT
> >    Because there are two matches for that pattern:
> >   - //devices/platform/…/target0:0:0/0:0:0:0/block/sda
> >   - //devices/platform/…/target0:0:0/0:0:0:0/block/sda/sda1
> > Both of them have SUBSYSTEM=="block", ACTION=="add",
> > ATTRS{idVendor}=="058f" and ATTRS{idProduct}=="6387".
> >
> > > If add ENV{DEVTYPE}=="usb_device" and change the
> > > SUBSYSTEM=="usb_device" , when plug usb, udev does nothing ...
> >    Because there is nothing that matches SUBSYSTEM=="usb_device".
> >
>
> Hi, thanks for your response.
>
> I understand, I add the size of partition sda1 for only match pattern
> --> ATTR{size}=="3930112"
>
> SUBSYSTEM=="block", ACTION=="add", ATTRS{idVendor}=="058f",
> ATTRS{idProduct}=="6387", ATTR{size}=="3930112",
> SYMLINK+="external%n", RUN+="/usr/local/bin/autobackup.sh"
>
> And now, only exec the script one time. The name of device change when
> connect different port usb...
>
> I have to put a more precise and less ugly rule. Maybe with KERNEL
> variable --> KERNEL=="sd*1" :
>
> SUBSYSTEM=="block", ACTION=="add", ATTRS{idVendor}=="058f",
> ATTRS{idProduct}=="6387", KERNEL=="sd*1", SYMLINK+="external%n",
> RUN+="/usr/local/bin/autobackup.sh"
>
> With these, works well!
>
> Thanks.
>

If you want udev to match on a specific USB stick partition, I would
recommend to match on something like the filesystem label (ID_FS_LABEL) or
filesystem UUID (ID_FS_UUID).

Personally I would go for the filesystem label, because then you can easily
create a new USB stick that matches: all you have to do is format the
filesystem with the same label.

Kind regards,
Maarten de Vries