[dm-devel] udev cookie on DM_DEVICE_RELOAD

[Hannes Reinecke]

Hi all,

I've been debugging weird failures in multipathing, where 'multipath
-r' would occasionally incide libdevmapper to create
device nodes under /dev/mapper on it's own, instead of relying on
udev for doing so.
Looking in the logs, I've found:

Jun 29 15:15:05 | libdevmapper: ioctl/libdm-iface.c(1725): dm reload
3600508b4000cf1c300008000002b0000  NF   [16384] (*1)
Jun 29 15:15:05 | libdevmapper: ioctl/libdm-iface.c(1689): Cookie
value is not set while trying to call DM_DEVICE_RESUME ioctl.
Please, consider using libdevmapper's udev synchronisation interface
or disable it explicitly by calling dm_udev_set_sync_support(0).
Jun 29 15:15:05 | libdevmapper: ioctl/libdm-iface.c(1691): Switching
off device-mapper and all subsystem related udev rules. Falling back
to libdevmapper node creation.

Okay, that'll explain it.
Then I've added a cookie to the call of DM_DEVICE_RELOAD, and
encountered a hang:
Jun 29 15:41:55 | 3600508b1001047395656543131580001: addmap [0
143305920 multipath 1 queue_if_no_path 0 1 1 service-time 0 1 1 104:0 1]
Jun 29 15:41:55 | libdevmapper: libdm-common.c(2105): Udev cookie
0xd4d7246 (semid 6062098) created
Jun 29 15:41:55 | libdevmapper: libdm-common.c(2125): Udev cookie
0xd4d7246 (semid 6062098) incremented to 1
Jun 29 15:41:55 | libdevmapper: libdm-common.c(1997): Udev cookie
0xd4d7246 (semid 6062098) incremented to 2
Jun 29 15:41:55 | libdevmapper: libdm-common.c(2238): Udev cookie
0xd4d7246 (semid 6062098) assigned to RELOAD task(1) with flags
DISABLE_LIBRARY_FALLBACK (0x20)
Jun 29 15:41:55 | libdevmapper: ioctl/libdm-iface.c(1725): dm reload
3600508b1001047395656543131580001  NNS    [16384] (*1)
Jun 29 15:41:55 | libdevmapper: libdm-common.c(2032): Udev cookie
0xd4d7246 (semid 6062098) decremented to 1
Jun 29 15:41:55 | libdevmapper: libdm-common.c(2288): Udev cookie
0xd4d7246 (semid 6062098) waiting for zero
(hangs)

So apparently you can only set the cookie for DM_DEVICE_RESUME,
_not_ DM_DEVICE_RELOAD.

Which is odd, as DM_DEVICE_RELOAD is the only call I'll ever do;
apparently it's being translated internally into a
suspend/reload/resume cycle.

Shouldn't device-mapper take care of setting the cookie correctly?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare at suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)