Public bug reported:
"multipath -r" causes the /dev/mapper/<wwid> to disappear momentarily,
which leads to some issue in consumer applications as such OpenStack.
After some investigation, I found that /dev/mapper/<wwid> was deleted by
udev during the reload, and it was re-created soon later by multipathd
(livdevmapper code of cause). Detailed findings are as follows:
For reload in domap (rename as well),
case ACT_RELOAD:
r = dm_addmap_reload(mpp, params);
if (r)
r = dm_simplecmd_noflush(DM_DEVICE_RESUME, mpp->alias,
0, MPATH_UDEV_RELOAD_FLAG);
break;
it passes 0 to dm_simplecmd_noflush as argument for needsync, which makes
dm_task_set_cookie call being skipped in dm_simplecmd,
if (udev_wait_flag && !dm_task_set_cookie(dmt, &cookie,
((conf->daemon)? DM_UDEV_DISABLE_LIBRARY_FALLBACK : 0) | udev_flags)) {
dm_udev_complete(cookie);
goto out;
}
because of the short-circuit evaluation. Thus _do_dm_ioctl in libdevmapper will
add DM_UDEV_DISABLE_DM_RULES_FLAG flag to dmi->event_nr, and that will
eventually be used in the udev rules (55-dm.rules),
ENV{DM_UDEV_DISABLE_DM_RULES_FLAG}!="1", ENV{DM_NAME}=="?*",
SYMLINK+="mapper/$env{DM_NAME}"
Since the DM_UDEV_DISABLE_DM_RULES_FLAG is set, the rule will not match. As a
result the link is removed.
** Affects: multipath-tools (Ubuntu)
Importance: Undecided
Assignee: Liang Chen (cbjchen)
Status: In Progress
** Changed in: multipath-tools (Ubuntu)
Status: New => In Progress
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https://bugs.launchpad.net/bugs/1621340
Title:
'multipath -r' causes /dev/mapper/<wwid> being removed
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