[Bug 644489] Re: constantly changes /dev/disk/by-id/{scsi, wwn}-* LUN symlinks with multipathing

[Peter Petrakis]

After chatting with Douglas Gilbert on this I know have a better
understanding of the problem. This very issue has been raised by
him before on linux-scsi and it never saw final resolution.

http://kerneltrap.org/mailarchive/linux-scsi/2010/2/15/6778453

When the file descriptor to the SD device is closed, the change
event occurs, presumably because it was opened with O_RDRW
to begin with, though nothing actually changed.

By changing that flag to O_RDONLY, no udev events are generated
when the fd closes. It doesn't address the root cause but it's
sufficient to get us unjammed safely while we continue to work
on a better solution. That solution may be adjusting the multipath
priority checkers to use the corresponding sg devices when 
presented with an sd device. Either way, there's more work to do.

Since all the priority checkers amount to different degrees of
scsi inquiry, and vendor specific san interrogation commands. I
believe we're safe with the O_RDONLY approach. All data
direction flags for sg io in this case are SG_DXFER_FROM_DEV
or SG_DXFER_NONE.


** Patch added: "multipath-tools-eliminate-udev-change-events-lp644489.debdiff"
   https://bugs.launchpad.net/ubuntu/+source/multipath-tools/+bug/644489/+attachment/2177364/+files/multipath-tools-eliminate-udev-change-events-lp644489.debdiff

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Title:
  constantly changes /dev/disk/by-id/{scsi,wwn}-* LUN symlinks with
  multipathing

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