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RE: [dm-devel] [Bug 164617] extracting tar image causes paths sta te change to [ready][failed]

On Fri, 29 Jul 2005 15:35:25 +0200
christophe varoqui <christophe varoqui free fr> wrote
> Subject: [dm-devel] [Bug 164617] extracting tar image causes paths
> 	state	change to [ready][failed]
> To: narasimha murthy hp com
> Cc: device-mapper development <dm-devel redhat com>
> Message-ID: <1122644125 3569 37 camel zezette>
> Content-Type: text/plain
> Will provide the following additional info :
> Was the daemon runing ?
> If so paste a verbose daemon log.
> Paste a dmesg too.

Talking with Narasimha on the weekly multipathing conference call,
it seems this problem only occurs when a second multipath mapped
device is manually created via dmsetup to utilize the SAME paths
as a multipath mapped device already configured by multipath(8).

Seems to me that neither multipath nor multipathd will react well
to this configuration since there is but a single path data structure
for each physical path and each path structure has but a single link
to its multipath data structure.

It also seems that the kernel dm code should not be allowing this to
happen, that is, a target device should not be used as a target of
more than a single device-mapper mapped device.

Target devices are claimed for use by but a single exclusive open via
a call to bd_claim in open_dev, but the device-mapper uses the same
claim holder value for all target devices -- thereby allowing the same
device to be a target device of multiple mapped devices.

A possible fix here is to use a claim holder value (ptr to mapped
device possibly) which is unique for each mapped device -- thereby
causing an attempt to create a mapped device using a target device
of an already existing mapped device to fail.

I can experiment with this and get a patch as soon as I have a host to use.

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