Re: [PATCH] Refuse to install on XFS destroying its superblock

[Robert Millan <rmh@aybabtu.com>]

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On Sat, Oct 17, 2009 at 12:18:05AM +0200, Vladimir 'phcoder' Serbinenko wrote:
>  2009-10-16  Vladimir Serbinenko  <phcoder@gmail.com>
>  
> +	* util/i386/pc/grub-setup.c (setup): Refuse to overwrite XFS superblock.
> +	(options): New option --destroy-xfs.
> +	(main): Handle --destroy-xfs.

I gave this some more thought, and I think this could be less ad-hoc.  We're
treating XFS as if it were a "weird", unique thing just because it isn't biased
towards DOS-style boot like most filesystems are.

Instead, I've done something more generic, using our standard filesystem
probing engine which should be more reliable than a single memcmp.

I propose the attached patch.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

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=== modified file 'ChangeLog'
--- ChangeLog	2009-10-16 20:21:12 +0000
+++ ChangeLog	2009-10-17 11:19:35 +0000
@@ -1,3 +1,13 @@
+2009-10-17  Robert Millan  <rmh.grub@aybabtu.com>
+
+	* include/grub/fs.h (struct grub_fs): Add `begins_at_first_sector'
+	member.
+	* fs/xfs.c (grub_xfs_fs): Initialize `begins_at_first_sector' to 1.
+	* util/i386/pc/grub-setup.c (setup): Add safety check that probes for
+	filesystems which begin at first sector.
+	(options): New option --skip-fs-probe.
+	(main): Handle --skip-fs-probe and pass it to setup().
+
 2009-10-16  Vladimir Serbinenko  <phcoder@gmail.com>
 
 	Let user specify OpenBSD root device.

=== modified file 'fs/xfs.c'
--- fs/xfs.c	2009-08-26 14:17:34 +0000
+++ fs/xfs.c	2009-10-17 11:19:35 +0000
@@ -805,6 +805,9 @@
     .close = grub_xfs_close,
     .label = grub_xfs_label,
     .uuid = grub_xfs_uuid,
+#ifdef GRUB_UTIL
+    .begins_at_first_sector = 1,
+#endif
     .next = 0
   };
 

=== modified file 'include/grub/fs.h'
--- include/grub/fs.h	2009-06-10 21:04:23 +0000
+++ include/grub/fs.h	2009-10-17 11:19:35 +0000
@@ -68,6 +68,12 @@
   /* Get writing time of filesystem. */
   grub_err_t (*mtime) (grub_device_t device, grub_int32_t *timebuf);
 
+#ifdef GRUB_UTIL
+  /* Whether this filesystem begins at first sector or reserves it for
+     DOS-style boot.  */
+  int begins_at_first_sector;
+#endif
+
   /* The next filesystem.  */
   struct grub_fs *next;
 };

=== modified file 'util/i386/pc/grub-setup.c'
--- util/i386/pc/grub-setup.c	2009-08-25 08:28:13 +0000
+++ util/i386/pc/grub-setup.c	2009-10-17 11:19:35 +0000
@@ -86,7 +86,7 @@
 static void
 setup (const char *dir,
        const char *boot_file, const char *core_file,
-       const char *root, const char *dest, int must_embed, int force)
+       const char *root, const char *dest, int must_embed, int force, int fs_probe)
 {
   char *boot_path, *core_path, *core_path_dev;
   char *boot_img, *core_img;
@@ -251,6 +251,16 @@
   if (grub_disk_read (dest_dev->disk, 0, 0, GRUB_DISK_SECTOR_SIZE, tmp_img))
     grub_util_error ("%s", grub_errmsg);
 
+  if (fs_probe)
+    {
+      grub_fs_t fs;
+      fs = grub_fs_probe (dest_dev);
+      if (fs && fs->begins_at_first_sector)
+	grub_util_error ("%s appears to contain a %s filesystem, which would be "
+			 "overwritten by grub-setup (--skip-fs-probe disables this "
+			 "check, use at your own risk).", dest_dev->disk->name, fs->name);
+    }
+
   /* Copy the possible DOS BPB.  */
   memcpy (boot_img + GRUB_BOOT_MACHINE_BPB_START,
 	  tmp_img + GRUB_BOOT_MACHINE_BPB_START,
@@ -556,6 +566,7 @@
     {"device-map", required_argument, 0, 'm'},
     {"root-device", required_argument, 0, 'r'},
     {"force", no_argument, 0, 'f'},
+    {"skip-fs-probe", no_argument, 0, 's'},
     {"help", no_argument, 0, 'h'},
     {"version", no_argument, 0, 'V'},
     {"verbose", no_argument, 0, 'v'},
@@ -580,6 +591,7 @@
   -m, --device-map=FILE   use FILE as the device map [default=%s]\n\
   -r, --root-device=DEV   use DEV as the root device [default=guessed]\n\
   -f, --force             install even if problems are detected\n\
+  -s, --skip-fs-probe     do not probe for filesystems in DEVICE\n\
   -h, --help              display this message and exit\n\
   -V, --version           print version information and exit\n\
   -v, --verbose           print verbose messages\n\
@@ -613,7 +625,7 @@
   char *dev_map = 0;
   char *root_dev = 0;
   char *dest_dev;
-  int must_embed = 0, force = 0;
+  int must_embed = 0, force = 0, fs_probe = 1;
 
   progname = "grub-setup";
 
@@ -666,6 +678,10 @@
 	    force = 1;
 	    break;
 
+	  case 's':
+	    fs_probe = 0;
+	    break;
+
 	  case 'h':
 	    usage (0);
 	    break;
@@ -767,7 +783,7 @@
 	  setup (dir ? : DEFAULT_DIRECTORY,
 		 boot_file ? : DEFAULT_BOOT_FILE,
 		 core_file ? : DEFAULT_CORE_FILE,
-		 root_dev, grub_util_get_grub_dev (devicelist[i]), 1, force);
+		 root_dev, grub_util_get_grub_dev (devicelist[i]), 1, force, fs_probe);
 	}
     }
   else
@@ -776,7 +792,7 @@
     setup (dir ? : DEFAULT_DIRECTORY,
 	   boot_file ? : DEFAULT_BOOT_FILE,
 	   core_file ? : DEFAULT_CORE_FILE,
-	   root_dev, dest_dev, must_embed, force);
+	   root_dev, dest_dev, must_embed, force, fs_probe);
 
   /* Free resources.  */
   grub_fini_all ();