Dne 25.7.2011 14:17, Kay Sievers napsal(a): > On Mon, Jul 25, 2011 at 12:12, Zdenek Kabelac <zkabelac@xxxxxxxxxx> wrote: >> Dne 25.7.2011 02:18, Kay Sievers napsal(a): >>> On Fri, 2011-07-22 at 16:22 +0200, Zdenek Kabelac wrote: >>> >>>> For now udev recieves 3 event for removal of DM logical volumes. (1 for >>>> bdi and 2 for same block kobject). Reason is dm device generates its >>>> own kobject event with approriate env parameter and block layer sends >>>> another KOBJ_REMOVE event on its own unconditionaly for the same >>>> kobject. As for now only the kobject cleanup checks that the REMOVE >>>> event has been already sent and avoids duplicate REMOVE event. >>> >>>> The patch for kobject_uevent_env() which has been testing for duplicate >>>> REMOVE event did not passed into the mainline (yet?): >>> >>> No, it's wasn't merged. Subsystems should really not send their own >>> 'add' or 'remove' events. These are properties of the driver core. >>> >>>> I'm proposing alternative way around to always use kobject cleanup >>>> routine for sending REMOVE event if it was not send by the module - so >>>> it makes the code few lines shorter. >>> >>> The events the core creates are only sent out at release() not at del(), >>> so we would delay 'remove' events when we keep the device pinned but >>> it's not valid anymore. We can not do that today, we would need to move >>> the core-created 'remove' events to del(). >>> >>> For device-mapper, I would prefer to add a '.dev_uevent' callback to the >>> 'block' class let this callback check 'struct block_device_operations' >>> for a possibly specified '.uevent' callback and call it. >>> >>> Then have 'dm_blk_dops' add '.uevent' and let the core call into the dm >>> code to the needed properties to the 'remove' event, instead of sending >>> its own, and see the duplication. >> >> Sounds like complex solution > > I don't think so, It's clean, ~30 lines long, and technically correct, I expect. Well then I've probably not fully understand your idea here - I guess it would then simpler written by you? >> maybe it would be easier to just register some >> environment variable on dm code side - like kobject_add_env() - so it would >> take envs from this internal kobject list and after sending uevent it would >> implicitly clear this list. > > So we would keep allocated per-event-type variables in the kobject, to > send when 'remove' is finally called? The callbacks are just much > simpler , I guess. No - nothing so complex - kobject would have the list - and you would be able to add some env param to this list - the nearest kobject_uevent() would just splice those parameters to the env list it wants to send (something like 10 lines of code). The only user would be probably dm so far - and it would check it wants to send REMOVE - and in this case it would add env to kobject and would skip kobject_uvent. On the other hand, it would probably extended kobject struct size without big use case - so Milan's solution that checks whether REMOVE has been already sent and skip all future REMOVE events seems by far the simplest here. I think your proposal also requires struct extension to store callback somewhere ? >> So in dm case dm-uevent would just register env(cookie) for KOBJ_REMOVE and >> would left kobject_uevent() on block layer ? >> >> Also I'm aware that remove event would be delayed by leaving it on >> kobject_cleanup(), but since you mentioned 'del()' as a better place - why not >> move this implicit uvent call there. > > It's probably not wrong to do that, but I don't remember now why we > added it to release() that time. del() looks like the best natural place here - and safe few lines of code ;) Zdenek -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
