[PATCH for-4.15?] docs/misc: xenstored: Re-instate and tweak the documentation for XS_RESUME

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

Commit 13dd372834a4 removed the documentation for XS_RESUME, however
this command is still implemented (at least in C Xenstored) and used by
libxl when resuming a domain.

So re-instate the documentation for the XS_RESUME. Take the opportunity
to update it as there is a user of the command.

Fixes: 13dd372834a4 ("docs/designs: re-work the xenstore migration document...")
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

---

Cc: raphning@xxxxxxxxx
Cc: jgross@xxxxxxxx
Cc: paul@xxxxxxx

Ian, would you still consider documentation update for 4.15?

I looked at the implementation of domain_resume() in Xen, it doesn't
look like we can get away with XS_RESUME because Xen will not send
VIRQ_DOM_EXC on resume.
---
 docs/misc/xenstore.txt | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/docs/misc/xenstore.txt b/docs/misc/xenstore.txt
index 148074233001..334dc8b6fdf5 100644
--- a/docs/misc/xenstore.txt
+++ b/docs/misc/xenstore.txt
@@ -294,6 +294,22 @@ IS_DOMAIN_INTRODUCED       <domid>|                T| or F|
        ie, if INTRODUCE for the domain has not yet been followed by
        domain destruction or explicit RELEASE.
 
+RESUME                 <domid>|
+
+       Arranges that @releaseDomain events will once more be
+       generated when the domain becomes shut down.  This might have
+       to be used if a domain were to be shut down (generating one
+       @releaseDomain) and then subsequently restarted, since the
+       state-sensitive algorithm in xenstored will not otherwise send
+       further watch event notifications if the domain were to be
+       shut down again.
+
+       This command will be issued in place such as resume because
+       Xen will "shutdown" the domain on suspend.
+
+       xenstored prevents the use of RESUME other than by dom0.
+
+
 SET_TARGET             <domid>|<tdomid>|
        Notifies xenstored that domain <domid> is targeting domain
        <tdomid>. This grants domain <domid> full access to paths
-- 
2.17.1