python: Workaround UNIX socket path length limits

From aa28e8bfb646a54ba91e3545f3c0b9db39eddb7f Mon Sep 17 00:00:00 2001
From: James Page <[email protected]>
Date: Wed, 16 Jan 2013 10:52:59 +0000
Subject: [PATCH] python: Workaround UNIX socket path length limits
To: [email protected]

UNIX socket paths have a limit in terms of length.  On Linux
this is 103 characters.

This is a problem in Debian/Ubuntu buildds which can generate
quite long paths.

This patch works around this issue by detecting when socket
connection/binding fails due to this issue and accessing the
socket path using a file descriptor path in /proc/self/fd.

The workaround is limited to Linux.

This is based on similar code in the C parts of OpenvSwitch.

Signed-off-by: James Page <[email protected]>
Signed-off-by: Ben Pfaff <[email protected]>

python/ovs/socket_util.py

@@ -70,9 +70,44 @@ def make_unix_socket(style, nonblock, bind_path, connect_path):
         return 0, sock
     except socket.error, e:
         sock.close()
-        if bind_path is not None:
+        if (bind_path is not None and
+            os.path.exists(bind_path)):
             ovs.fatal_signal.unlink_file_now(bind_path)
-        return get_exception_errno(e), None
+        eno = ovs.socket_util.get_exception_errno(e)
+        if (eno == "AF_UNIX path too long" and
+            os.uname()[0] == "Linux"):
+            short_connect_path = None
+            short_bind_path = None
+            connect_dirfd = None
+            bind_dirfd = None
+            # Try workaround using /proc/self/fd
+            if connect_path is not None:
+                dirname = os.path.dirname(connect_path)
+                basename = os.path.basename(connect_path)
+                try:
+                    connect_dirfd = os.open(dirname, os.O_DIRECTORY | os.O_RDONLY)
+                except OSError, err:
+                    return get_exception_errno(e), None
+                short_connect_path = "/proc/self/fd/%d/%s" % (connect_dirfd, basename)
+
+            if bind_path is not None:
+                dirname = os.path.dirname(bind_path)
+                basename = os.path.basename(bind_path)
+                try:
+                    bind_dirfd = os.open(dirname, os.O_DIRECTORY | os.O_RDONLY)
+                except OSError, err:
+                    return get_exception_errno(e), None
+                short_bind_path = "/proc/self/fd/%d/%s" % (bind_dirfd, basename)
+
+            try:
+                return make_unix_socket(style, nonblock, short_bind_path, short_connect_path)
+            finally:
+                if connect_dirfd is not None:
+                    os.close(connect_dirfd)
+                if bind_dirfd is not None:
+                    os.close(bind_dirfd)
+        else:
+            return get_exception_errno(e), None
 
 
 def check_connection_completion(sock):