Re: [Qemu-devel] [PATCH 05/11] snapshot: add paired functions for internal snapshot id and name

[Wenchao Xia]

于 2013-6-11 17:14, Stefan Hajnoczi 写道:

On Sat, Jun 08, 2013 at 02:58:01PM +0800, Wenchao Xia wrote:

+/*
+ * Every internal snapshot have an ID used by qemu block layer, this function
+ * check whether name used by user mess up with ID. An empty string is also
+ * invalid.
+ */
+bool snapshot_name_wellformed(const char *name)
+{
+    char *p;
+    /* variable v is used to remove gcc warning of "ignoring return value" and
+       "set but not used" */
+    unsigned long v;
+
+    if (*name == '\0') {
+        return false;
+    }
+
+    v = strtoul(name, &p, 10);
+    v++;
+
+    if (*p == '\0') {
+        /* Numeric string */
+        return false;
+    }
+    return true;
+}

Shorter function with the same behavior and a rewritten doc comment:

/*
  * Return true if the given internal snapshot name is valid, false
  * otherwise.
  *
  * To prevent clashes with internal snapshot IDs, names consisting only
  * of digits are rejected.  Empty strings are also rejected.
  */
bool snapshot_name_wellformed(const char *name)
{
     return strspn(name, "0123456789") != strlen(name);
}

  much nicer, will use it, thanks!

+
+/* Following function generate id string, used by block driver, such as qcow2.
+   Since no better place to go, place the funtion here for now. */
+void snapshot_id_string_generate(int id, char *id_str, int id_str_size)
+{
+    snprintf(id_str, id_str_size, "%d", id);
+}

Since the caller has to manage id, this function doesn't really abstract
anything.  I would keep the snprintf() inline, there's only one caller.

  Its purpose is move the id rules from one implemention(qcow2) into
generic. If not, it would be a question why snapshot_name_wellformed()
could make sure name not conflict with ID, then reader find the answer
in qcow2...
  I think at least a document is needed about how should implemention
under ./block generate snapshot ID.

--
Best Regards

Wenchao Xia