Re: [Xen-devel] [PATCH 16/19] libxl: suspend: Abolish usleeps in domain suspend wait

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Jackson writes ("Re: [PATCH 16/19] libxl: suspend: Abolish usleeps in 
domain suspend wait"):
> Reading xenstored_core.c suggests both read and write give EINVAL.  So
> making xswait work for it would indeed involve special-casing @ in
> libxl.

I looked at how this would seem in the API and it's very simple.  See
below.

I think I should probably add this to my series and use it in the
later patch.

Ian.

From 41abced84e669449a926ca38a78194a2188c7cff Mon Sep 17 00:00:00 2001
From: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Date: Fri, 14 Mar 2014 17:38:38 +0000
Subject: [PATCH] libxl: events: libxl__xswait* support @paths

Special-case paths starting with '@' in libxl__xswait.  Attempting to
read these from xenstore gives EINVAL.  Callers waiting for (say)
@releaseDomain will be checking for some condition which can be
observed other than by looking at xenstore.

Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
---
 tools/libxl/libxl_aoutils.c  |    8 ++++++--
 tools/libxl/libxl_internal.h |    2 ++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c
index 477717b..1c9eb9e 100644
--- a/tools/libxl/libxl_aoutils.c
+++ b/tools/libxl/libxl_aoutils.c
@@ -69,8 +69,12 @@ void xswait_xswatch_callback(libxl__egc *egc, 
libxl__ev_xswatch *xsw,
     int rc;
     const char *data;
 
-    rc = libxl__xs_read_checked(gc, XBT_NULL, xswa->path, &data);
-    if (rc) { xswait_report_error(egc, xswa, rc); return; }
+    if (xswa->path[0] == '@') {
+        data = 0;
+    } else {
+        rc = libxl__xs_read_checked(gc, XBT_NULL, xswa->path, &data);
+        if (rc) { xswait_report_error(egc, xswa, rc); return; }
+    }
 
     xswa->callback(egc, xswa, 0, data);
 }
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 644fcee..dc3d34c 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1110,6 +1110,8 @@ typedef struct libxl__xswait_state libxl__xswait_state;
  *     This HAS been logged.
  *     xswait will not continue (but calling libxl__xswait_stop is OK).
  *
+ * xswait.path may start with with '@', in which case no read is done
+ * and the callback will always get data==0.
  */
 typedef void libxl__xswait_callback(libxl__egc *egc,
       libxl__xswait_state *xswa, int rc, const char *data);
-- 
1.7.10.4


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