[2/5] xen/xenbus: Add 'will_handle' callback support in xenbus_watch_path()

[2/5] xen/xenbus: Add 'will_handle' callback support in xenbus_watch_path()

Origin: https://git.kernel.org/linus/2e85d32b1c865bec703ce0c962221a5e955c52c2
Bug: https://xenbits.xen.org/xsa/advisory-349.html
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-29568

Some code does not directly make 'xenbus_watch' object and call
'register_xenbus_watch()' but use 'xenbus_watch_path()' instead.  This
commit adds support of 'will_handle' callback in the
'xenbus_watch_path()' and it's wrapper, 'xenbus_watch_pathfmt()'.

This is part of XSA-349

Cc: stable@vger.kernel.org
Signed-off-by: SeongJae Park <sjpark@amazon.de>
Reported-by: Michael Kurth <mku@amazon.de>
Reported-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name xen-xenbus-Add-will_handle-callback-support-in-xenbu.patch