Add check for speed (takes 33 minutes on my laptop, OUCH!)

Make xenstored use tdb, transactions can soft-fail (EAGAIN)
Transactions no longer take root dir, no longer lock & block: commit can fail spuriously with EAGAIN, not ETIMEDOUT.
Speeds up transactions by over 1000 times, should be NFS safe.
New program: xs_tdb_dump to dump raw TDB contents.
Don't do failure testing: we are no longer robust against all ENOMEM 8(
Introduce "struct node" which contains perms, children and data.
Make struct xs_permissions unpadded, so we can write to tdb w/o valgrind complaints.
Gently modify TDB to use talloc, not do alloc on tdb_delete.

Fix up transaction users for new semantics.
Don't need a transaction around a single read in xen/i386/kernel/smpboot.c.
Python: transaction_start() returns True/False rather than raising exception on EAGAIN.
Fix usage comment on xs_transaction_end().
Include stdarg to xs_tdb_dump so it compiles.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tools/python/xen/lowlevel/xs/xs.c

@@ -582,9 +582,8 @@ static PyObject *xspy_unwatch(PyObject *self, PyObject *args, PyObject *kwds)
 }
 
 #define xspy_transaction_start_doc "\n"				\
-	"Start a transaction on a path.\n"			\
+	"Start a transaction.\n"				\
 	"Only one transaction can be active at a time.\n"	\
-	" path [string]: xenstore path.\n"			\
 	"\n"							\
 	"Returns None on success.\n"				\
 	"Raises RuntimeError on error.\n"			\
@@ -593,8 +592,8 @@ static PyObject *xspy_unwatch(PyObject *self, PyObject *args, PyObject *kwds)
 static PyObject *xspy_transaction_start(PyObject *self, PyObject *args,
                                         PyObject *kwds)
 {
-    static char *kwd_spec[] = { "path", NULL };
-    static char *arg_spec = "s|";
+    static char *kwd_spec[] = { NULL };
+    static char *arg_spec = "";
     char *path = NULL;
 
     struct xs_handle *xh = xshandle(self);
@@ -606,7 +605,7 @@ static PyObject *xspy_transaction_start(PyObject *self, PyObject *args,
     if (!PyArg_ParseTupleAndKeywords(args, kwds, arg_spec, kwd_spec, &path))
         goto exit;
     Py_BEGIN_ALLOW_THREADS
-    xsval = xs_transaction_start(xh, path);
+    xsval = xs_transaction_start(xh);
     Py_END_ALLOW_THREADS
     if (!xsval) {
         PyErr_SetFromErrno(PyExc_RuntimeError);
@@ -623,7 +622,7 @@ static PyObject *xspy_transaction_start(PyObject *self, PyObject *args,
 	"Attempts to commit the transaction unless abort is true.\n"	\
 	" abort [int]: abort flag (default 0).\n"			\
 	"\n"								\
-	"Returns None on success.\n"					\
+	"Returns True on success, False if you need to try again.\n"	\
 	"Raises RuntimeError on error.\n"				\
 	"\n"
 
@@ -646,11 +645,16 @@ static PyObject *xspy_transaction_end(PyObject *self, PyObject *args,
     xsval = xs_transaction_end(xh, abort);
     Py_END_ALLOW_THREADS
     if (!xsval) {
+	if (errno == EAGAIN) {
+	    Py_INCREF(Py_False);
+	    val = Py_False;
+	    goto exit;
+	}
         PyErr_SetFromErrno(PyExc_RuntimeError);
         goto exit;
     }
-    Py_INCREF(Py_None);
-    val = Py_None;
+    Py_INCREF(Py_True);
+    val = Py_True;
  exit:
     return val;
 }

tools/python/xen/xend/XendDomainInfo.py

@@ -839,20 +839,20 @@ class XendDomainInfo:
         """Release all vm devices.
         """
 
-        t = xstransact("%s/device" % self.path)
-
-        for n in controllerClasses.keys():
-            for d in t.list(n):
-                try:
-                    t.remove(d)
-                except ex:
-                    # Log and swallow any exceptions in removal -- there's
-                    # nothing more we can do.
-                    log.exception(
-                        "Device release failed: %s; %s; %s; %s" %
-                        (self.info['name'], n, d, str(ex)))
-        t.commit()
-
+        while True:
+            t = xstransact("%s/device" % self.path)
+            for n in controllerClasses.keys():
+                for d in t.list(n):
+                    try:
+                        t.remove(d)
+                    except ex:
+                        # Log and swallow any exceptions in removal --
+                        # there's nothing more we can do.
+                        log.exception(
+                           "Device release failed: %s; %s; %s; %s" %
+                            (self.info['name'], n, d, str(ex)))
+            if t.commit():
+                break
 
     def eventChannel(self, path=None):
         """Create an event channel to the domain.

tools/python/xen/xend/server/DevController.py

@@ -126,20 +126,21 @@ class DevController:
         compulsory to use it; subclasses may prefer to allocate IDs based upon
         the device configuration instead.
         """
-        path = self.frontendMiscPath()
-        t = xstransact(path)
-        try:
-            result = t.read("nextDeviceID")
-            if result:
-                result = int(result)
-            else:
-                result = 1
-            t.write("nextDeviceID", str(result + 1))
-            t.commit()
-            return result
-        except:
-            t.abort()
-            raise
+        while True:
+            path = self.frontendMiscPath()
+            t = xstransact(path)
+            try:
+                result = t.read("nextDeviceID")
+                if result:
+                    result = int(result)
+                else:
+                    result = 1
+                t.write("nextDeviceID", str(result + 1))
+                if t.commit():
+                    return result
+            except:
+                t.abort()
+                raise
 
 
     ## private:

tools/python/xen/xend/xenstore/xsnode.py

@@ -280,8 +280,8 @@ class XenStore:
                                (', while writing %s : %s' % (str(path),
                                                              str(data))))
 
-    def begin(self, path):
-        self.getxs().transaction_start(path)
+    def begin(self):
+        self.getxs().transaction_start()
 
     def commit(self, abandon=False):
         self.getxs().transaction_end(abort=abandon)

tools/python/xen/xend/xenstore/xstransact.py

@@ -14,16 +14,8 @@ class xstransact:
     def __init__(self, path):
         self.in_transaction = False
         self.path = path.rstrip("/")
-        while True:
-            try:
-                xshandle().transaction_start(path)
-                self.in_transaction = True
-                return
-            except RuntimeError, ex:
-                if ex.args[0] == errno.ENOENT and path != "/":
-                    path = "/".join(path.split("/")[0:-1]) or "/"
-                else:
-                    raise
+        xshandle().transaction_start()
+        self.in_transaction = True
 
     def __del__(self):
         if self.in_transaction:
@@ -175,14 +167,8 @@ class xstransact:
             t = cls(path)
             try:
                 v = t.read(*args)
-                t.commit()
-                return v
-            except RuntimeError, ex:
                 t.abort()
-                if ex.args[0] == errno.ETIMEDOUT:
-                    pass
-                else:
-                    raise
+                return v
             except:
                 t.abort()
                 raise
@@ -194,14 +180,8 @@ class xstransact:
             t = cls(path)
             try:
                 t.write(*args, **opts)
-                t.commit()
-                return
-            except RuntimeError, ex:
-                t.abort()
-                if ex.args[0] == errno.ETIMEDOUT:
-                    pass
-                else:
-                    raise
+                if t.commit():
+                    return
             except:
                 t.abort()
                 raise
@@ -217,14 +197,8 @@ class xstransact:
             t = cls(path)
             try:
                 t.remove(*args)
-                t.commit()
-                return
-            except RuntimeError, ex:
-                t.abort()
-                if ex.args[0] == errno.ETIMEDOUT:
-                    pass
-                else:
-                    raise
+                if t.commit():
+                    return
             except:
                 t.abort()
                 raise
@@ -236,14 +210,8 @@ class xstransact:
             t = cls(path)
             try:
                 v = t.list(*args)
-                t.commit()
-                return v
-            except RuntimeError, ex:
-                t.abort()
-                if ex.args[0] == errno.ETIMEDOUT:
-                    pass
-                else:
-                    raise
+                if t.commit():
+                    return v
             except:
                 t.abort()
                 raise
@@ -255,14 +223,8 @@ class xstransact:
             t = cls(path)
             try:
                 v = t.gather(*args)
-                t.commit()
-                return v
-            except RuntimeError, ex:
-                t.abort()
-                if ex.args[0] == errno.ETIMEDOUT:
-                    pass
-                else:
-                    raise
+                if t.commit():
+                    return v
             except:
                 t.abort()
                 raise
@@ -274,14 +236,8 @@ class xstransact:
             t = cls(path)
             try:
                 v = t.store(*args)
-                t.commit()
-                return v
-            except RuntimeError, ex:
-                t.abort()
-                if ex.args[0] == errno.ETIMEDOUT:
-                    pass
-                else:
-                    raise
+                if t.commit():
+                    return v
             except:
                 t.abort()
                 raise