On Tue, 2022-02-01 at 11:11 +0100, Zdenek Kabelac wrote: > > > > > > But yes, if temporarily losing the symlink causes issues, your > > > patch > > > solves that (Zdenek will push that upstream). > > > > Thank you very much! It occured to me that if we want to solve my > > use > > case with minimal risk, we could make the the case in which the > > symlinks are preserved conditional on ACTION=="add" (i.e. true > > coldplug > > events). Tell me if you'd prefer that, I can re-submit. > > The problem is handling of 'suspended' state in udev rules - as I've > mentioned > original no userland tool should mostly care about this. > > However since there are those things like udev 'trigger' and it would > be kind > of ugly if the 'left-over' suspended device would stop whole system > operation > it's most likely better ATM to have some kind of support for this. > > It's should be noted there is still 'race' risk of system freezing in > the case > the suspend happens just after sysfs test and before actual i.e. > 'blkid' use. Right. Even if blkid was smart enough to check immediately before doing I/O on the device, there would still be a race window. It occured to me that it might be useful if IO on suspended DM devices failed with -EAGAIN when opened with a non-blocking file descriptor. But I haven't thought it through ... I suppose that would have other issues, it would be a breaking change anyway. The good thing is that most of the time, the devices are suspended only for a short period of time, so blkid will just hang for a few fractions of a second. The fact that udev skips calling blkid is only for the very rare remaining cases in which the suspend state persists for a long time. > The missed issue to be solve is - that ALL rules have to rely on a > single > suspend check - otherwise we risk 'partial' processing which is the > last > thing we want to see (aka all or nothing). Don't we have that already? Isn't that the check that sets the DM_SUSPENDED flag? > Your real problem was not the suspend on its own - which still may > happen > anytime (so i.e. just after the test whether device is suspended), > but the bug was related to bad exit path cleaning udev db content in > this case > - which is clear bug. Next bug is that other rules have to be > consistent and > properly skip its processing if the 1st. rules decides its meant to > be skipped. Part of the consistency problem is that we have a lot of related but not equivalent udev variables: DM_SUSPENDED DM_NOSCAN DM_UDEV_DISABLE_OTHER_RULES_FLAG DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG DM_UDEV_DISABLE_DISK_RULES_FLAG and then of course SYSTEMD_READY MPATH_DEVICE_READY For consumers of these variables (i.e. udev rules from other subsystems), it's not always obvious which one they should look at (just my €0.02). Regards, Martin -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
