[Xen-devel] [PATCH] Protocol change of suspending through xenbus

[Frank Pan <frankpzh@xxxxxxxxx>]

Xend/libxl uses polling on suspending PV/PV-on-HVM guests.
They simply check whether the guest has been suspended again
and again. Guest has no chance to report errors to Xend/libxl.

The following patch is for libxl. It creates a key in the xenbus:
control/shutdown-error. Guest can post any error string into this
key, and also libxl can return this error to the user/administrator
asap.

Signed-off-by: Frank Pan <frankpzh@xxxxxxxxx>
---
 tools/libxl/libxl_create.c |    3 ++-
 tools/libxl/libxl_dom.c    |   26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletions(-)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index d94480e..95795e0 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -287,7 +287,8 @@ int libxl__domain_make(libxl_ctx *ctx,
libxl_domain_create_info *info,
     libxl__gc gc = LIBXL_INIT_GC(ctx); /* fixme: should be done by caller */
     int flags, ret, i, rc;
     char *uuid_string;
-    char *rw_paths[] = { "control/shutdown", "device",
"device/suspend/event-channel" , "data"};
+    char *rw_paths[] = { "control/shutdown", "control/shutdown-error",
+                         "device", "device/suspend/event-channel" , "data"};
     char *ro_paths[] = { "cpu", "memory", "device", "error", "drivers",
                          "control", "attr", "messages" };
     char *dom_path, *vm_path;
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index c702cf7..42c5e79 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -438,9 +438,35 @@ static int
libxl__domain_suspend_common_callback(void *data)
     LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "wait for the guest to suspend");
     watchdog = 60;
     while (watchdog > 0) {
+        char *err_path, *err_msg;
         xc_domaininfo_t info;

         usleep(100000);
+
+        /*
+         * Check if guest returns an error.
+         */
+        err_path = libxl__sprintf(si->gc, "%s/control/shutdown-error",
+                                  libxl__xs_get_dompath(si->gc, si->domid));
+      retry_transaction1:
+        t = xs_transaction_start(ctx->xsh);
+
+        err_msg = libxl__xs_read(si->gc, t, err_path);
+
+        if (strlen(err_msg))
+            libxl__xs_write(si->gc, t, err_path, "");
+
+        if (!xs_transaction_end(ctx->xsh, t, 0))
+            if (errno == EAGAIN)
+                goto retry_transaction1;
+
+        if (strlen(err_msg)) {
+            LIBXL__LOG(ctx, LIBXL__LOG_ERROR,
+                       "guest returns error on suspending: %s,
request cancelled",
+                       err_msg);
+            return 0;
+        }
+
         ret = xc_domain_getinfolist(ctx->xch, si->domid, 1, &info);
         if (ret == 1 && info.domain == si->domid && info.flags &
XEN_DOMINF_shutdown) {
             int shutdown_reason;
-- 
1.7.0.4

-- 
æéç, Frank Pan

Computer Science and Technology
Tsinghua University

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