Dne 11.6.2015 v 04:54 M.H. Tsai napsal(a):
2015-06-08 15:17 GMT+08:00 Zdenek Kabelac <zkabelac@redhat.com>:
It doesn't really matter here what you could confirm here - there is a race
you can't avoid - i.e. udev is completely 'independent' and may execute
trigger udev rules at any random point in time or some other command may try
to open device in parallel (i.e. 'dd')
So the only way how to ensure there is no such race - is to deactivate such
device (which should be possible - since as you said - noone has it open)
Also remember - activation routine is 'separate' from command code - as it
could run on a completely different node - so you cannot 'validate' from
command code there is no user of a device on 'activation' node unless device
is locally active.
Thus going through the proper sequence of steps and allowing udev to
properly synchronize (i.e. you should not 'mix' activation & deactivation
under same cookie) is clearly the best way how to achieve your desired goal.
Hi,
Sorry for opening this question again. I could image the potential problem in
name swapping. But does that mean, It's even unrecommended to rename
an active device, although the target name are not used? The renaming path
in LVM is not suggested ?
## this is not recommended
# lvchange -ay vg1/lv1
# lvrename vg1/lv1 vg1/lv2
## do this instead
# lvchange -an vg1/lv1
# lvrename vg1/lv1 vg1/lv2
Rename is fine as long as you are not reusing names while devices are still
active.
Check which devices names are reported by i.e. mount after you rename a device
- keep devices mounted and do rename like this:
lvcreate lv1
mkfs,mount lv1
lvrename lv1 -> lv2
lvcreate lv3
mkfs,mount lv3
lvrename lv3 -> lv1
Check 'mount' result or /proc/self/mountinfo
So doing such 'live' rename may lead to major confusion of system admin -
since those device names might be completely different from reality in your
/dev dir.
Zdenek
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