tools/xenstore: remember global and per domain max accounting values

Add saving the maximum values of the different accounting data seen
per domain and (for unprivileged domains) globally, and print those
values via the xenstore-control quota command. Add a sub-command for
resetting the global maximum values seen.

This should help for a decision how to set the related quotas.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>

docs/misc/xenstore.txt

@@ -426,7 +426,7 @@ CONTROL			<command>|[<parameters>|]
 	print|<string>
 		print <string> to syslog (xenstore runs as daemon) or
 		to console (xenstore runs as stubdom)
-	quota|[set <name> <val>|<domid>]
+	quota|[set <name> <val>|<domid>|max [-r]]
 		without parameters: print the current quota settings
 		with "set <name> <val>": set the quota <name> to new value
 		<val> (The admin should make sure all the domain usage is
@@ -435,6 +435,9 @@ CONTROL			<command>|[<parameters>|]
 		violating the new quota setting isn't increased further)
 		with "<domid>": print quota related accounting data for
 		the domain <domid>
+		with "max [-r]": show global per-domain maximum values of all
+		unprivileged domains, optionally reset the values by adding
+		"-r"
 	quota-soft|[set <name> <val>]
 		like the "quota" command, but for soft-quota.
 	help			<supported-commands>