[PATCH] xl: fix block-attach command parsing

[Jeremy Fitzhardinge <jeremy@goop.org>]

Fix two command-line parsing problems:
 - the argc check is wrong: it must be provided with the frontend device
 - the ro/rw mode is optional, so default to rw if it is absent

Also, update the usage message accordingly.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff -r 0f0a25c4c991 tools/libxl/xl_cmdimpl.c
--- a/tools/libxl/xl_cmdimpl.c	Thu May 20 09:18:33 2010 -0700
+++ b/tools/libxl/xl_cmdimpl.c	Thu May 20 14:37:24 2010 -0700
@@ -3444,7 +3444,7 @@
     uint32_t fe_domid, be_domid = 0;
     libxl_device_disk disk = { 0 };
 
-    if ((argc < 3) || (argc > 6)) {
+    if ((argc < 4) || (argc > 6)) {
         help("block-attach");
         exit(0);
     }
@@ -3489,7 +3489,7 @@
     }
     disk.virtpath = argv[3];
     disk.unpluggable = 1;
-    disk.readwrite = (argv[4][0] == 'w') ? 1 : 0;
+    disk.readwrite = (argc <= 4 || argv[4][0] == 'w') ? 1 : 0;
 
     if (domain_qualifier_to_domid(argv[1], &fe_domid, 0) < 0) {
         fprintf(stderr, "%s is an invalid domain identifier\n", argv[1]);
diff -r 0f0a25c4c991 tools/libxl/xl_cmdtable.c
--- a/tools/libxl/xl_cmdtable.c	Thu May 20 09:18:33 2010 -0700
+++ b/tools/libxl/xl_cmdtable.c	Thu May 20 14:37:24 2010 -0700
@@ -216,7 +216,7 @@
     { "block-attach",
       &main_blockattach,
       "Create a new virtual block device",
-      "<Domain> <BackDev> <FrontDev> <Mode> [BackDomain]",
+      "<Domain> <BackDev> <FrontDev> [<Mode>] [BackDomain]",
     },
     { "block-list",
       &main_blocklist,