git-p4: input to "p4 files" by stdin instead of arguments

This approach, suggested by Alex Riesen, bypasses the need for xargs-style
argument list handling. The handling in question looks broken in a corner
case with SC_ARG_MAX=4096 and final argument over 96 characters.

Signed-off-by: Scott Lamb <slamb@slamb.org>
Signed-off-by: Simon Hausmann <simon@lst.de>

contrib/fast-import/git-p4

@@ -725,27 +725,13 @@ class P4Sync(Command):
         if not files:
             return
 
-        # We cannot put all the files on the command line
-        # OS have limitations on the max lenght of arguments
-        # POSIX says it's 4096 bytes, default for Linux seems to be 130 K.
-        # and all OS from the table below seems to be higher than POSIX.
-        # See http://www.in-ulm.de/~mascheck/various/argmax/
-        if (self.isWindows):
-            argmax = 2000
-        else:
-            argmax = min(4000, os.sysconf('SC_ARG_MAX'))
-
-        chunk = ''
-        filedata = []
-        for i in xrange(len(files)):
-            f = files[i]
-            chunk += '"%s#%s" ' % (f['path'], f['rev'])
-            if len(chunk) > argmax or i == len(files)-1:
-                data = p4CmdList('print %s' % chunk)
-                if "p4ExitCode" in data[0]:
-                    die("Problems executing p4. Error: [%d]." % (data[0]['p4ExitCode']));
-                filedata.extend(data)
-                chunk = ''
+        filedata = p4CmdList('-x - print',
+                             stdin='\n'.join(['%s#%s' % (f['path'], f['rev'])
+                                              for f in files]),
+                             stdin_mode='w+')
+        if "p4ExitCode" in filedata[0]:
+            die("Problems executing p4. Error: [%d]."
+                % (filedata[0]['p4ExitCode']));
 
         j = 0;
         contents = {}