[PATCH 3/3] powerpc/pseries: Expose post-migration in kernel device tree update to drmgr

[Michael Ellerman]

On Fri, 2015-02-27 at 18:24 -0800, Tyrel Datwyler wrote:
> Traditionally after a migration operation drmgr has coordinated the device tree
> update with the kernel in userspace via the ugly /proc/ppc64/ofdt interface. This
> can be better done fully in the kernel where support already exists. Currently,
> drmgr makes a faux ibm,suspend-me RTAS call which we intercept in the kernel so
> that we can check VASI state for suspendability. After the LPAR resumes and
> returns to drmgr that is followed by the necessary update-nodes and
> update-properties RTAS calls which are parsed and communitated back to the kernel
> through /proc/ppc64/ofdt for the device tree update. The drmgr tool should
> instead initiate the migration using the already existing
> /sysfs/kernel/mobility/migration entry that performs all this work in the kernel.
> 
> This patch adds a show function to the sysfs "migration" attribute that returns
> 1 to indicate the kernel will perform the device tree update after a migration
> operation and that drmgr should initiated the migration through the sysfs
> "migration" attribute.

I don't understand why we need this?

Can't drmgr just check if /sysfs/kernel/mobility/migration exists, and if so it
knows it should use it and that the kernel will handle the whole procedure?

cheers