RUN rules to enable/disable printer queues

RUN rules to enable/disable printer queues

[Zack Weinberg]

I have a USB printer which is turned off most of the time.  I want to have
the computer automatically run "lpc start" and "lpc stop" on the relevant
print queue when the printer is turned on and off, respectively.

I tried to do this with this rule:

BUS="usb", SYSFS{product}="Lexmark Optra E310", SYSFS{serial}="0101137", \
    SYMLINK="lp_epson", RUN+="/etc/udev/scripts/lpqueue.sh"

where lpqueue.sh is a little script I wrote that maps ACTION­d to lpc
start, and ACTION=remove to lpc stop.

This correctly creates and deletes the lp_epson symlink, but lpqueue.sh is
only invoked on add events, not remove events, so it can only do half of
its job.  I believe that the rule *does* match on both add and remove,
because if it didn't match on remove, it wouldn't know to delete the
symlink; so there must be some quirk with RUN= that is not mentioned in
the manual...  Any ideas?

I am using udev 068 as packaged by Debian unstable, in conjunction with
kernel 2.6.12.5 (prepackaged Debian kernel, linux-image-2.6.12-1-686-smp).

As a side note, it isn't terribly important to me as I only have the one
printer, but I have to hardwire the name of the print queue in lpqueue.sh
because there isn't enough info passed in its environment to tell one USB
printer from another.  If the SYMLINK list were made available to RUN
scripts, the script could then do the right thing for an arbitrary number
of printers.  (This would be useful to someone who had both a color inkjet
and a B/W laser printer attached to the same computer via USB, say.)

zw



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Re: RUN rules to enable/disable printer queues

[Kay Sievers]

On Thu, Aug 25, 2005 at 05:43:53PM -0700, Zack Weinberg wrote:
> I have a USB printer which is turned off most of the time.  I want to have
> the computer automatically run "lpc start" and "lpc stop" on the relevant
> print queue when the printer is turned on and off, respectively.
> 
> I tried to do this with this rule:
> 
> BUS="usb", SYSFS{product}="Lexmark Optra E310", SYSFS{serial}="0101137", \
>     SYMLINK="lp_epson", RUN+="/etc/udev/scripts/lpqueue.sh"
> 
> where lpqueue.sh is a little script I wrote that maps ACTION­d to lpc
> start, and ACTION=remove to lpc stop.
> 
> This correctly creates and deletes the lp_epson symlink, but lpqueue.sh is
> only invoked on add events, not remove events, so it can only do half of
> its job. 

Use two rules, one for ACTION="add" and one for "remove" if you want to
name the device at the same time. The SYMLINK key prevents rule to be catched
by a "remove" cause it is only valid to _create_ a link - same for NAME, OWNER,
GROUP, MODE.

> I believe that the rule *does* match on both add and remove,
> because if it didn't match on remove, it wouldn't know to delete the
> symlink

udev has it's own database to remember the created nodes and symlinks.
On remove everything that was created with add is removed without a
explicit rule.

Kay


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Re: RUN rules to enable/disable printer queues

[Zack Weinberg]

Kay Sievers said:

> Use two rules, one for ACTION="add" and one for "remove" if you want to
> name the device at the same time. The SYMLINK key prevents rule to be
> catched by a "remove" cause it is only valid to _create_ a link - same
> for NAME, OWNER, GROUP, MODE.

Okay, so now I have

    BUS="usb", SYSFS{product}="Lexmark Optra E310", \
    SYSFS{serial}="0101137", ACTION="remove", \
        RUN+="/etc/udev/scripts/lpqueue.sh"

    BUS="usb", SYSFS{product}="Lexmark Optra E310", \
    SYSFS{serial}="0101137", ACTION="add", \
        SYMLINK="lp_epson", RUN+="/etc/udev/scripts/lpqueue.sh"

... and it still doesn't work: lpqueue.sh is invoked only on add, not remove.

Even if it did work, I would not be happy about having to duplicate the
BUS=..., SYSFS{product}=..., SYSFS{serial}=... piece.  The constraint
you describe (SYMLINK, NAME, etc. implicitly restricting rules to add
events) is silly, because RUN= may do something useful with that
information on remove events as well (or could, if it were all being put
into the environment, as it ought to be).

zw



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Re: RUN rules to enable/disable printer queues

[Kay Sievers]

On Thu, Aug 25, 2005 at 08:06:05PM -0700, Zack Weinberg wrote:
> Kay Sievers said:
> 
> > Use two rules, one for ACTION="add" and one for "remove" if you want to
> > name the device at the same time. The SYMLINK key prevents rule to be
> > catched by a "remove" cause it is only valid to _create_ a link - same
> > for NAME, OWNER, GROUP, MODE.
> 
> Okay, so now I have
> 
>     BUS="usb", SYSFS{product}="Lexmark Optra E310", \
>     SYSFS{serial}="0101137", ACTION="remove", \
>         RUN+="/etc/udev/scripts/lpqueue.sh"

> ... and it still doesn't work: lpqueue.sh is invoked only on add, not remove.

The device is removed, so sysfs is obviously not available.

Kay


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Re: RUN rules to enable/disable printer queues

[Ian Pilcher]

Kay Sievers wrote:
> udev has it's own database to remember the created nodes and symlinks.
> On remove everything that was created with add is removed without a
> explicit rule.

In the future, perhaps it would be possible to add a "destructor" to
the database, a program that would be automatically run before the
device is actually removed.  This would obviate the need for separate
rules.

-- 
====================================
Ian Pilcher                                        i.pilcher@comcast.net
====================================



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Re: RUN rules to enable/disable printer queues

[Kay Sievers]

[-- Attachment #1: Type: text/plain, Size: 1366 bytes --]

On Fri, Aug 26, 2005 at 01:46:25PM +0200, Kay Sievers wrote:
> On Thu, Aug 25, 2005 at 08:06:05PM -0700, Zack Weinberg wrote:
> > Kay Sievers said:
> > 
> > > Use two rules, one for ACTION="add" and one for "remove" if you want to
> > > name the device at the same time. The SYMLINK key prevents rule to be
> > > catched by a "remove" cause it is only valid to _create_ a link - same
> > > for NAME, OWNER, GROUP, MODE.
> > 
> > Okay, so now I have
> > 
> >     BUS=="usb", SYSFS{product}=="Lexmark Optra E310", \
> >     SYSFS{serial}=="0101137", ACTION=="remove", \
> >         RUN+="/etc/udev/scripts/lpqueue.sh"
> 
> > ... and it still doesn't work: lpqueue.sh is invoked only on add, not remove.
> 
> The device is removed, so sysfs is obviously not available.

The attached patch should make it possible to store a variable in the
environment and at the same time in the udev database. This variable is
also available at "remove":
  ACTION=="add", KERNEL=="sda", ENV{MY_DEVICE}="1234", RUN+="/bin/logger add $devpath"
  ACTION=="remove", ENV{MY_DEVICE}=="1234", RUN+="/bin/logger remove $devpath"

This way it is also possible to export "remove" values, that are used in a RUN
key:
  ACTION=="add", KERNEL=="sda", ENV{MY_REMOVE}="/bin/logger remove $devpath", RUN+="/bin/logger add $devpath"
  ACTION=="remove", ENV{MY_REMOVE}!="", RUN+="$env{MY_REMOVE}"

Kay

[-- Attachment #2: udev-env-at-remove-01.patch --]
[-- Type: text/plain, Size: 1183 bytes --]

diff --git a/udev_event.c b/udev_event.c
--- a/udev_event.c
+++ b/udev_event.c
@@ -91,15 +91,21 @@ int udev_process_event(struct udev_rules
 			}
 			sysfs_close_class_device(class_dev);
 		} else if (strcmp(udev->action, "remove") == 0) {
+			struct name_entry *name_loop;
+
+			/* get data from db, remove db-entry, delete node */
 			dbg("node remove");
+			retval = udev_remove_device(udev);
+
+			/* restore stored persistent data */
+			list_for_each_entry(name_loop, &udev->env_list, node)
+				putenv(name_loop->name);
+
 			udev_rules_get_run(rules, udev, NULL, NULL);
 			if (udev->ignore_device) {
 				dbg("device event will be ignored");
 				return -1;
 			}
-
-			/* get name from db, remove db-entry, delete node */
-			retval = udev_remove_device(udev);
 		}
 
 		/* export name of device node or netif */
diff --git a/udev_rules.c b/udev_rules.c
--- a/udev_rules.c
+++ b/udev_rules.c
@@ -859,6 +859,7 @@ try_parent:
 			const char *key_name = key_pair_name(rule, pair);
 			const char *value = key_val(rule, &pair->key);
 
+			name_list_key_add(&udev->env_list, key_name, value);
 			setenv(key_name, value, 1);
 			dbg("export ENV '%s=%s'", key_name, value);
 		}