targetcli: serialize multiple requests

Problem:
-------
targetcli/rtslib cannot handle parallel requests at the moment.
Read more about this at http://bit.ly/targetcli-parallel-requests-issue

$ for i in {1..10}; do \
 targetcli /backstores/fileio create ${i} /tmp/file${i} 10M& done

Created fileio 1 with size 10485760
This _Backstore already exists in configFS
This _Backstore already exists in configFS
This _Backstore already exists in configFS
This _Backstore already exists in configFS
This _Backstore already exists in configFS
Created fileio 6 with size 10485760
Created fileio 2 with size 10485760
This _Backstore already exists in configFS
Created fileio 8 with size 10485760
Created fileio 9 with size 10485760

bails-out most of the time with above errors and sometimes even crashes.

Solution:
--------
Serialize/defend the parallel requests by simply taking a wait lock at
targetcli level, so that only one request can be processed by targetcli at
any given point in time.

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>

1 files changed, 0 insertions, 47 deletions

diff --git a/daemon/targetclid b/daemon/targetclid
index b909c6e..06ffbe8 100755
--- a/daemon/targetclid
+++ b/daemon/targetclid
@@ -44,8 +44,6 @@ class TargetCLI:
         self.socket_path = '/var/run/targetclid.sock'
         # pid file for defending on multiple daemon runs
         self.pid_file = '/var/run/targetclid.pid'
-        # lockfile for serializing multiple client requests
-        self.lock_file = '/var/run/targetclid.lock'
 
         self.NoSignal = True
 
@@ -85,16 +83,6 @@ class TargetCLI:
             self.pfd.close()
             sys.exit(1)
 
-        try:
-            self.lkfd = open(self.lock_file, 'w+');
-        except IOError as e:
-            self.display(
-                self.render(
-                    "opening lockfile failed: %s" %str(e),
-                    'red'))
-            self.pfd.close()
-            sys.exit(1)
-
         # Keep track, for later use
         self.con_stdout_ = self.con._stdout
         self.con_stderr_ = self.con._stderr
@@ -104,9 +92,6 @@ class TargetCLI:
         '''
         destructor
         '''
-        if not self.lkfd.closed:
-            self.lkfd.close()
-
         if not self.pfd.closed:
             self.pfd.close()
 
@@ -149,40 +134,10 @@ class TargetCLI:
         self.pfd.close()
 
 
-    def try_op_lock(self):
-        '''
-        acquire a blocking lock on lockfile, to serialize multiple client requests
-        '''
-        try:
-            fcntl.flock(self.lkfd, fcntl.LOCK_EX)  # wait here until ongoing request is finished
-        except Exception, e:
-            self.display(
-                self.render(
-                    "taking lock on lockfile failed: %s" %str(e),
-                    'red'))
-            sys.exit(1)
-
-
-    def release_op_lock(self):
-        '''
-        release blocking lock on lockfile, which can allow other requests process
-        '''
-        try:
-            fcntl.flock(self.lkfd, fcntl.LOCK_UN)  # allow other requests now
-        except Exception, e:
-            self.display(
-                self.render(
-                    "unlock on lockfile failed: %s" %str(e),
-                    'red'))
-            sys.exit(1)
-
-
     def client_thread(self, connection):
         '''
         Handle commands from client
         '''
-        self.try_op_lock()
-
         still_listen = True
         # Receive the data in small chunks and retransmit it
         while still_listen:
@@ -212,8 +167,6 @@ class TargetCLI:
                 connection.sendall(var)    # length of string
                 connection.sendall(output) # actual string
 
-        self.release_op_lock()
-
 
 def usage():
     print("Usage: %s [--version|--help]" % sys.argv[0], file=err)