[dm-devel] [PATCH 0/3] New approach at handling changed WWIDs

[Martin Wilck]

On Mon, 2019-03-25 at 17:27 -0500, Benjamin Marzinski wrote:
> 
> > One remark: With the kernel exporting the VPD pages in sysfs
> > and my late "multipath -u" patch series, udev should be able to
> > process
> > uevents for path devices without a single actual device IO. (*) 
> > While there are still possible causes for udev processing to get
> > stuck,
> > this would make it much less likely.
> 
> For reasons I don't understand, not all devices get a vpd_pg83 sysfs
> file, even though they clearly have a page 0x83, since multipath and
> sg_inq can read from it via ioctl.  I have a device like this. This
> is
> quite possibly a kernel issue that should get fixed, but regardless,
> it's been there for a while, and I just cheked and it still exists in
> the 5.0.0-rc6 kernel.

This is intentional. The kernel applies conservative heuristics to
determine whether these VPDs are supported. See the comment in
scsi_device_supports_vpd(). Sometimes the kernel gets it wrong, usually
because the device claims to be a pre-SCSI_SPC_2 device. Such devices
should be fixed with the BLIST_TRY_VPD_PAGES device flag if they do
support the DI VPD.

OPEN-V devices are a notorious example. But meanwhile the blist flags
are in place for them.

Regards
Martin

-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)