[dm-devel] [PATCH 2/3] dm: Start pr_reserve from the same starting path

[Christoph Hellwig]

On Thu, Jul 14, 2022 at 07:34:57PM -0500, Mike Christie wrote:
> I also ran the libiscsi PGR tests. We pass all of those tests except the
> Write Exclusive and Exclusive Access tests. I don't think those reservation
> types make sense for multipath devices though. And as I write this I'm
> thinking we should add a check for these types and just return failure).

Why would any reservation type make less sense for multipath vs
non-multipath setups/

> 
> 
> > systems that don't have the requirement to pin the PR to a device?
> 
> I didn't find any real applications that use the All Registrants type of
> reservation where every registered path is a reservation holder. However,
> libiscsi has PGR tests for that type of reservation and the code works ok.

Well.  In general ALL_TG_PT would usually be the preferred method
everywhere.  But that assumes:

 1) it actually is supported by the target
 2) the target actually has a useful concept of the Linux system being
    a single initiator, which outside of a few setups like software
    only iSCSI are rarely true

so we usually have to fall back to just registering every path
separately.