[Xen-devel] [PATCH] libxl: trigger attach events for devices attached before xl devd startup

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

When this daemon is started after creating backend device, that device
will not be configured.

Racy situation:
1. driver domain is started
2. frontend domain is started (just after kicking driver domain off)
3. device in frontend domain is connected to the backend (as specified
   in frontend domain configuration)
4. xl devd is started in driver domain

End result is that backend device in driver domain is not configured
(like network interface is not enabled), so the device doesn't work.

Fix this by artifically triggering events for devices already present in
xenstore before xl devd is started. Do this only after xenstore watch is
already registered, and only for devices not already initialized (in
XenbusStateInitWait state).

Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
 tools/libxl/libxl.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 1c81239..99815a7 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -4743,8 +4743,16 @@ int libxl_device_events_handler(libxl_ctx *ctx,
     uint32_t domid;
     libxl__ddomain ddomain;
     char *be_path;
+    char **kinds = NULL, **domains = NULL, **devs = NULL;
+    const char *sstate;
+    char *state_path;
+    int state;
+    unsigned int nkinds, ndomains, ndevs;
+    int i, j, k;
+    xs_transaction_t t;
 
     ddomain.ao = ao;
+    FILLZERO(ddomain.watch);
     LIBXL_SLIST_INIT(&ddomain.guests);
 
     rc = libxl__get_domid(gc, &domid);
@@ -4762,9 +4770,41 @@ int libxl_device_events_handler(libxl_ctx *ctx,
                                     be_path);
     if (rc) goto out;
 
+    rc = libxl__xs_transaction_start(gc, &t);
+    if (rc) goto out;
+    kinds = libxl__xs_directory(gc, t, be_path, &nkinds);
+    if (kinds) {
+        for (i = 0; i < nkinds; i++) {
+            domains = libxl__xs_directory(gc, t,
+                    GCSPRINTF("%s/%s", be_path, kinds[i]), &ndomains);
+            if (!domains)
+                continue;
+            for (j = 0; j < ndomains; j++) {
+                devs = libxl__xs_directory(gc, t,
+                        GCSPRINTF("%s/%s/%s", be_path, kinds[i], domains[j]), 
&ndevs);
+                if (!devs)
+                    continue;
+                for (k = 0; k < ndevs; k++) {
+                    state_path = GCSPRINTF("%s/%s/%s/%s/state",
+                            be_path, kinds[i], domains[j], devs[k]);
+                    rc = libxl__xs_read_checked(gc, t, state_path, &sstate);
+                    if (rc)
+                        continue;
+                    state = atoi(sstate);
+                    if (state == XenbusStateInitWait)
+                        backend_watch_callback(egc, &ddomain.watch,
+                                be_path, state_path);
+                }
+            }
+        }
+    }
+
+    libxl__xs_transaction_abort(gc, &t);
+
     return AO_INPROGRESS;
 
 out:
+    libxl__ev_xswatch_deregister(gc, &ddomain.watch);
     return AO_CREATE_FAIL(rc);
 }
 
-- 
2.5.5


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