Bug#580972: multipath-tools: unnecessary call to multipath in /etc/udev/rules.d/z60_multipath.rules

[Apollon Oikonomopoulos]

Package: multipath-tools
Version: 0.4.8-14+lenny2
Severity: normal

Hi,

/etc/udev/rules.d/z60_multipath.rules, as shipped with all debian packages up
to sid's version, contains the following rules:

RUN+="socket:/org/kernel/dm/multipath_event"
ACTION=="add|change", SUBSYSTEM=="block", RUN+="/sbin/multipath -v0 /dev/$name"

Multipathd itself has uevent support, which is what the first rule is used for.
However, the second rule is redundant and useful only in the case of block
devices showing up during boot, between /etc/init.d/multipath-tools-boot and
/etc/init.d/multipath-tools. Furthermore, it causes major system load whenever
a bulk of new LUNs are added to a running system. In our case, adding 10 LUNs
with 8 paths each causes the system load to rocket to 70-80 for 25s, while 80
multipath processes are racing to coallesce the multipaths. Disabling the
second rule causes the whole process to finish in less than 2 seconds while
multipathd itself handles the uevents generated by the kernel.

It should be noted that upstream do not include the second rule in their sample
rulefile[1].

Thus, the second rule should be removed or at least check whether multipathd is
running before executing /sbin/multipath.

One final note: multipathd uevent handling is broken with kernel 2.6.32, fixed
in a backwards compatible way upstream with commit
7fa7affc3d23dd9dc906804d22a61144bca9f9b9 (already present in squeeze/sid).
I know this is more of a wishlist item, but please backport the fix if possible
to make lenny's multipathd usable with newer kernels.

Thank you

-- System Information:
Debian Release: 5.0.4
  APT prefers stable
  APT policy: (500, 'stable'), (80, 'testing'), (70, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.32-trunk-amd64 (SMP w/2 CPU cores)
Locale: LANG=el_GR.UTF-8, LC_CTYPE=el_GR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash