Hi,

-----Original Message-----
From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
owner@vger.kernel.org] On Behalf Of Neil Brown
Sent: Monday, November 22, 2010 6:02 AM
To: Hawrylewicz Czarnowski, Przemyslaw
Cc: linux-raid@vger.kernel.org; Neubauer, Wojciech; Williams, Dan J;
Ciechanowski, Ed; Labun, Marcin; Czarnowska, Anna
Subject: Re: Autorebuild, new dynamic udev rules for hot-plugs

On Fri, 19 Nov 2010 15:12:19 +0000
"Hawrylewicz Czarnowski, Przemyslaw"
[off-list ref] wrote:

quoted

Hi,

I would like to present another patch for our autorebuild tree (it should

be applied on the top of Autorebuild series, as devel-3.2 is not stable
yet). Dan Williams proposed to reduce overhead associated with passing each
hot-plugged block device to mdadm, using just the devices described in
policies via mdadm.conf file.

quoted

See patch below for details, comments are as always very welcome.

I am in general in favour of this approach.
It has the benefit that it can very easily be not-used if there turn out to
be problems with it.

Four comments.

1/ I wouldn't write a file in /lib/udev/rules.d/
  I think it should be written to "/dev/.udev/rules.d/"
  which is referred to as the "temporary rules directory"
  in the udev documentation.

I am not sure if it is what we are looking for. Temporary means they disappear after reboot. It is OK as cold-plug does not need support for bare disks (or maybe I am wrong?). But in such case, one who wants to use autorebuild should invoke mdadm --activate-domains for example in /etc/init.d/local.boot or somewhere else. Second idea here is to use ActivateDomain() when one starts monitor with autorebuild enabled. Which one? I would prefer to leave it as it was written initially (considering comment #4). Then, if one removes policies from config, invoking --activate-domains should reset/remove rules (but see #3)

2/ I would be good to process the type=disk or type=part part of the
   policy into the rules file as well.

OK

3/ I'm not very comfortable with hard-coding the name of the
   file to be created in the rules.d directory.  Maybe usage could be
      --activate-domains=63-md-whatever

Good idea, but only if we store our rules in /dev/.udev/rules.d. Otherwise it would be difficult to maintain all generated rules and remove the old ones... I would leave default if not given by user, but one can pass any file name.

4/ I don't think it is good to have an incomplete file in rules.d that udev
   might accidentally read.  We should create the file with a name with a
   leading '.' (assuming udev ignores those, I haven't checked) and then
   rename it after it has been completely written.

You're right. In theory, such partial udev rules are excluded when udev can't interpret them properly. I have looked into udev's sources and found that it looks for "*.rules" files. All other file extensions are ignored. Files with leading dots are also omitted. I would prefer to create <name>.temp file and then rename it into <name>.rules.

Other than that, it looks pretty good.

Great

Thanks,
NeilBrown

quoted

Date: Thu, 18 Nov 2010 01:19:52 +0100
Subject: [PATCH] New dynamic hot-plug udev rules for policies

When introducing policies, new hot-plug rules were added to support
bare disks. Mdadm was started for each hot plugged block device
to determine if it could be used as spare or as a replacement member for
degraded array.
This patch introduces limitation of range of devices that are handled
by mdadm. It limits them to the ones specified in domains associated
with the actions: spare-same-port, spare and spare-force.
In order to enable hot-plug for bare disks one must update udev rules
with command

	mdadm --activate-domains

After mdadm.conf is changed one is obliged to re-run
"mdadm --activate-domains" command in order to bring the system
configuration up to date.
All hot-plugged disks containing metadata are still handled by existing
rules.

Note: this patch is just a proposition to minimize overhead of using

mdadm for

quoted

each plugged block device. If accepted, it will be incorporated in
previous implementation of hot-plug for bare disks.

Signed-off-by: Przemyslaw Czarnowski

[off-list ref]

quoted

---
 Makefile           |    2 +
 ReadMe.c           |    1 +
 mdadm.c            |    4 ++
 mdadm.h            |    9 +++-
 policy.c           |  137

++++++++++++++++++++++++++++++++++++++++++++++++++++

quoted

 udev-md-raid.rules |    5 +-
 6 files changed, 154 insertions(+), 4 deletions(-)

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