libxl: introduce libxl_userdata_unlink

This will be used in later patch for xl to remove its "xl" userdata
file.

Both CTX lock and userdata lock are taken in this API. CTX lock is taken
to maintain locking hierarchy, but it also has a side effect to protect
against R-M-W by other threads. Userdata lock is used to protect against
domain destruction.

In general application should not rely on these internal locks to
protect its own userdata files. It should deploys its own lock if it
cares.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 3bee6596da218fe4266e1da0729fe09f6a714375..bc68cacdda4f3a01b322bb1ee57e7c6b7c08830b 100644 (file)
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -67,6 +67,13 @@
  * the same $(XEN_VERSION) (e.g. throughout a major release).
  */
 
+/* LIBXL_HAVE_USERDATA_UNLINK
+ *
+ * If it is defined, libxl has a library function called
+ * libxl_userdata_unlink.
+ */
+#define LIBXL_HAVE_USERDATA_UNLINK 1
+
 /* LIBXL_HAVE_CPUPOOL_QUALIFIER_TO_CPUPOOLID
  *
  * If this is defined, libxl has a library function called
@@ -1268,6 +1275,9 @@ int libxl_userdata_retrieve(libxl_ctx *ctx, uint32_t domid,
    * data_r and datalen_r may be 0.
    * On error return, *data_r and *datalen_r are undefined.
    */
+int libxl_userdata_unlink(libxl_ctx *ctx, uint32_t domid,
+                          const char *userdata_userid);
+
 
 int libxl_get_physinfo(libxl_ctx *ctx, libxl_physinfo *physinfo);
 int libxl_set_vcpuaffinity(libxl_ctx *ctx, uint32_t domid, uint32_t vcpuid,

diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index 02384acdf74cb0531b1297dbedddae08149ed893..ce0c4ac771d2ab48125a509ff83469c2bfb9e646 100644 (file)
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -2016,6 +2016,32 @@ out:
     return rc;
 }
 
+int libxl_userdata_unlink(libxl_ctx *ctx, uint32_t domid,
+                          const char *userdata_userid)
+{
+    GC_INIT(ctx);
+    int rc;
+
+    libxl__domain_userdata_lock *lock;
+    const char *filename;
+
+    CTX_LOCK;
+    lock = libxl__lock_domain_userdata(gc, domid);
+    if (!lock) {
+        rc = ERROR_LOCK_FAIL;
+        goto out;
+    }
+
+    filename = libxl__userdata_path(gc, domid, userdata_userid, "d");
+    if (unlink(filename)) rc = ERROR_FAIL;
+
+    libxl__unlock_domain_userdata(lock);
+out:
+    CTX_UNLOCK;
+    GC_FREE;
+    return rc;
+}
+
 /*
  * Local variables:
  * mode: C