[PATCH v3] cmp: Only return success when both files have the same contents

[Glenn Washburn]

This allows the cmp command to be used in GRUB scripts to conditionally
run commands based on whether two files are the same.

The command is now quiet by default and the -v switch can be given to enable
verbose mode, the previous behavior.

Update documentation accordingly.

Suggested-by: Li Gen <ligenlive@gmail.com>
Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 docs/grub.texi           | 12 ++++++++----
 grub-core/commands/cmp.c | 38 +++++++++++++++++++++++++-------------
 2 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/docs/grub.texi b/docs/grub.texi
index ff44b1cbe9..1752fcb7db 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4508,9 +4508,14 @@ on platforms that support CMOS.
 @node cmp
 @subsection cmp
 
-@deffn Command cmp file1 file2
-Compare the file @var{file1} with the file @var{file2}. If they differ
-in size, print the sizes like this:
+@deffn Command cmp [@option{-v}] file1 file2
+Compare the file @var{file1} with the file @var{file2}. If they are completely
+identical, @code{$?} will be set to 0. Otherwise, if the files are not 
identical,
+@code{$?} will be set to a nonzero value.
+
+By default nothing will be output. If the @option{-v} is used, verbose mode is
+enabled. In this mode when when the files differ in size, print the sizes like
+this:
 
 @example
 Differ in size: 0x1234 [foo], 0x4321 [bar]
@@ -4523,7 +4528,6 @@ bytes like this:
 Differ at the offset 777: 0xbe [foo], 0xef [bar]
 @end example
 
-If they are completely identical, nothing will be printed.
 @end deffn
 
 
diff --git a/grub-core/commands/cmp.c b/grub-core/commands/cmp.c
index e9c3b25d34..46185fbbcb 100644
--- a/grub-core/commands/cmp.c
+++ b/grub-core/commands/cmp.c
@@ -22,14 +22,21 @@
 #include <grub/file.h>
 #include <grub/mm.h>
 #include <grub/command.h>
+#include <grub/extcmd.h>
 #include <grub/i18n.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
 #define BUFFER_SIZE 512
 
+static const struct grub_arg_option options[] =
+  {
+    {0, 'v', 0, N_("Enable verbose output"), 0, 0},
+    {0, 0, 0, 0, 0, 0}
+  };
+
 static grub_err_t
-grub_cmd_cmp (grub_command_t cmd __attribute__ ((unused)),
+grub_cmd_cmp (grub_extcmd_context_t ctxt,
              int argc, char **args)
 {
   grub_ssize_t rd1, rd2;
@@ -38,19 +45,20 @@ grub_cmd_cmp (grub_command_t cmd __attribute__ ((unused)),
   grub_file_t file2 = 0;
   char *buf1 = 0;
   char *buf2 = 0;
+  grub_err_t err = GRUB_ERR_TEST_FAILURE;
 
   if (argc != 2)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("two arguments expected"));
 
-  grub_printf_ (N_("Compare file `%s' with `%s':\n"), args[0],
-               args[1]);
+  if (ctxt->state[0].set)
+    grub_printf_ (N_("Compare file `%s' with `%s':\n"), args[0], args[1]);
 
   file1 = grub_file_open (args[0], GRUB_FILE_TYPE_CMP);
   file2 = grub_file_open (args[1], GRUB_FILE_TYPE_CMP);
   if (! file1 || ! file2)
     goto cleanup;
 
-  if (grub_file_size (file1) != grub_file_size (file2))
+  if (ctxt->state[0].set && (grub_file_size (file1) != grub_file_size (file2)))
     grub_printf_ (N_("Files differ in size: %llu [%s], %llu [%s]\n"),
                  (unsigned long long) grub_file_size (file1), args[0],
                  (unsigned long long) grub_file_size (file2), args[1]);
@@ -78,9 +86,10 @@ grub_cmd_cmp (grub_command_t cmd __attribute__ ((unused)),
            {
              if (buf1[i] != buf2[i])
                {
-                 grub_printf_ (N_("Files differ at the offset %llu: 0x%x [%s], 
0x%x [%s]\n"),
-                               (unsigned long long) (i + pos), buf1[i],
-                               args[0], buf2[i], args[1]);
+                 if (ctxt->state[0].set)
+                   grub_printf_ (N_("Files differ at the offset %llu: 0x%x 
[%s], 0x%x [%s]\n"),
+                                 (unsigned long long) (i + pos), buf1[i],
+                                 args[0], buf2[i], args[1]);
                  goto cleanup;
                }
            }
@@ -90,7 +99,9 @@ grub_cmd_cmp (grub_command_t cmd __attribute__ ((unused)),
       while (rd2);
 
       /* TRANSLATORS: it's always exactly 2 files.  */
-      grub_printf_ (N_("The files are identical.\n"));
+      if (ctxt->state[0].set)
+        grub_printf_ (N_("The files are identical.\n"));
+      err = GRUB_ERR_NONE;
     }
 
 cleanup:
@@ -102,18 +113,19 @@ cleanup:
   if (file2)
     grub_file_close (file2);
 
-  return grub_errno;
+  return err;
 }
 
-static grub_command_t cmd;
+static grub_extcmd_t cmd;
 
 GRUB_MOD_INIT(cmp)
 {
-  cmd = grub_register_command ("cmp", grub_cmd_cmp,
-                              N_("FILE1 FILE2"), N_("Compare two files."));
+  cmd = grub_register_extcmd ("cmp", grub_cmd_cmp, 0,
+                             N_("FILE1 FILE2"), N_("Compare two files."),
+                             options);
 }
 
 GRUB_MOD_FINI(cmp)
 {
-  grub_unregister_command (cmd);
+  grub_unregister_extcmd (cmd);
 }
-- 
2.34.1