ioemu: Re-enable guest boot with blktap devices (Weekly VMX status report. Xen: #18577 & Xen0: #696)

[Yosuke Iwamatsu <y-iwamatsu@ab.jp.nec.com>]

Li, Haicheng wrote:
> Our testing was blocke by bug #1367; and totally 2 new issues were found this week,
> 
> New Bugs:
> =====================================================================
> 1. [Qcow]Guest cannot boot up with Qcow image
> http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1367

Bug #1367 looks caused by the xenstore path checking code recently added
to ioemu-remote. I saw the same problem and found that the code didn't
consider the case blktap devices were attached to the guest. The patch
below should avoid the problem.

Signed-off-by: Yosuke Iwamatsu <y-iwamatsu@ab.jp.nec.com>

diff --git a/xenstore.c b/xenstore.c
index f5aa8a7..39ff8a6 100644
--- a/xenstore.c
+++ b/xenstore.c
@@ -158,6 +158,7 @@ static void xenstore_get_backend_path(char 
**backend, const char *devtype,
      char *frontend_path=0;
      char *backend_dompath=0;
      char *expected_backend=0;
+    char *expected_devtype=0;
      char *frontend_backend_path=0;
      char *backend_frontend_path=0;
      char *frontend_doublecheck=0;
@@ -191,11 +192,18 @@ static void xenstore_get_backend_path(char 
**backend, const char *devtype,
      backend_dompath = xs_get_domain_path(xsh, domid_backend);
      if (!backend_dompath) goto out;

+    if (pasprintf(&expected_devtype, "%s", devtype) == -1) goto out;
+
+ again:
      if (pasprintf(&expected_backend, "%s/backend/%s/%lu/%s",
-                  backend_dompath, devtype, frontend_domid, inst_danger)
+                  backend_dompath, expected_devtype, frontend_domid, 
inst_danger)
          == -1) goto out;

      if (strcmp(bpath, expected_backend)) {
+        if (!strcmp(expected_devtype, "vbd")) {
+            pasprintf(&expected_devtype, "tap");
+            goto again;
+        }
          fprintf(stderr, "frontend `%s' expected backend `%s' got `%s',"
                  " ignoring\n", frontend_path, expected_backend, bpath);
          errno = EINVAL;
@@ -223,6 +231,7 @@ static void xenstore_get_backend_path(char 
**backend, const char *devtype,
      free(frontend_path);
      free(backend_dompath);
      free(expected_backend);
+    free(expected_devtype);
      free(frontend_backend_path);
      free(backend_frontend_path);
      free(frontend_doublecheck);