Re: grub-probe detects ext4 wronly as ext2

["Javier Martín" <lordhabbit@gmail.com>]

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El mié, 04-02-2009 a las 08:41 +0100, Felix Zielcke escribió:
> Am Montag, den 11.08.2008, 16:14 +0200 schrieb Javier Martín:
> > Hi there,
> > 
> > After reading Felix's reply I've once again found your post and
> > implemented your request, so here is a new version of the patch
> > ("version 6"). Sorry for missing your message in the first instance...
> > u_u
> 
> I'd like to bring this up again.
> Now with that journal_dev bug (See [0] or [1]) it would be really nice
> to have this commited.
> 
> [0] http://lists.gnu.org/archive/html/grub-devel/2009-02/msg00018.html
> [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=502333

Well, I am happy to post a diff of the patch against current SVN head
(r1973). I have personally confirmed (in a VM) that it:
1) Still builds (and even runs! ^^)
2) Works with existing ext2/3 file systems (I haven't checked ext4 FSs
but the "extents" bit is marked as supported, so it should work)
3) Correctly rejects journal devices, which will then appear as "unknown
filesystem" when accessed.

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Index: fs/ext2.c
===================================================================
--- fs/ext2.c	(revisión: 1973)
+++ fs/ext2.c	(copia de trabajo)
@@ -71,8 +71,53 @@
          ? EXT2_GOOD_OLD_INODE_SIZE \
          : grub_le_to_cpu16 (data->sblock.inode_size))
 
-#define EXT3_FEATURE_COMPAT_HAS_JOURNAL	0x0004
+/* Superblock filesystem feature flags (RW compatible)
+ * A filesystem with any of these enabled can be read and written by a driver
+ * that does not understand them without causing metadata/data corruption */
+#define EXT2_FEATURE_COMPAT_DIR_PREALLOC	0x0001
+#define EXT2_FEATURE_COMPAT_IMAGIC_INODES	0x0002
+#define EXT3_FEATURE_COMPAT_HAS_JOURNAL		0x0004
+#define EXT2_FEATURE_COMPAT_EXT_ATTR		0x0008
+#define EXT2_FEATURE_COMPAT_RESIZE_INODE	0x0010
+#define EXT2_FEATURE_COMPAT_DIR_INDEX		0x0020
+/* Superblock filesystem feature flags (RO compatible)
+ * A filesystem with any of these enabled can be safely read by a driver that
+ * does not understand them, but should not be written to, usually because
+ * additional metadata is required */
+#define EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER	0x0001
+#define EXT2_FEATURE_RO_COMPAT_LARGE_FILE	0x0002
+#define EXT2_FEATURE_RO_COMPAT_BTREE_DIR	0x0004
+#define EXT4_FEATURE_RO_COMPAT_GDT_CSUM		0x0010
+#define EXT4_FEATURE_RO_COMPAT_DIR_NLINK	0x0020
+#define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE	0x0040
+/* Superblock filesystem feature flags (back-incompatible)
+ * A filesystem with any of these enabled should not be attempted to be read
+ * by a driver that does not understand them, since they usually indicate
+ * metadata format changes that might confuse the reader. */
+#define EXT2_FEATURE_INCOMPAT_COMPRESSION	0x0001
+#define EXT2_FEATURE_INCOMPAT_FILETYPE		0x0002
+#define EXT3_FEATURE_INCOMPAT_RECOVER		0x0004 /* Needs recovery */
+#define EXT3_FEATURE_INCOMPAT_JOURNAL_DEV	0x0008 /* Volume is journal device */
+#define EXT2_FEATURE_INCOMPAT_META_BG		0x0010
+#define EXT4_FEATURE_INCOMPAT_EXTENTS		0x0040 /* Extents used */
+#define EXT4_FEATURE_INCOMPAT_64BIT		0x0080
+#define EXT4_FEATURE_INCOMPAT_FLEX_BG		0x0200
 
+/* The set of back-incompatible features this driver DOES support. Add (OR)
+ * flags here as the related features are implemented into the driver */
+#define EXT2_DRIVER_SUPPORTED_INCOMPAT ( EXT2_FEATURE_INCOMPAT_FILETYPE \
+                                       | EXT4_FEATURE_INCOMPAT_EXTENTS )
+/* List of rationales for the ignored "incompatible" features:
+ * needs_recovery: Not really back-incompatible - was added as such to forbid
+ *                 ext2 drivers from mounting an ext3 volume with a dirty
+ *                 journal because they will ignore the journal, but the next
+ *                 ext3 driver to mount the volume will find the journal and
+ *                 replay it, potentially corrupting the metadata written by
+ *                 the ext2 drivers
+ */
+#define EXT2_DRIVER_IGNORED_INCOMPAT ( EXT3_FEATURE_INCOMPAT_RECOVER )
+
+
 #define EXT3_JOURNAL_MAGIC_NUMBER	0xc03b3998U
 
 #define EXT3_JOURNAL_DESCRIPTOR_BLOCK	1
@@ -486,10 +531,12 @@
   return 0;
 }
 
+#define EXT2_DRIVER_MOUNT_FAIL(message) { local_error = (message); goto fail; }
 static struct grub_ext2_data *
 grub_ext2_mount (grub_disk_t disk)
 {
   struct grub_ext2_data *data;
+  const char *local_error = 0;
 
   data = grub_malloc (sizeof (struct grub_ext2_data));
   if (!data)
@@ -498,13 +545,19 @@
   /* Read the superblock.  */
   grub_disk_read (disk, 1 * 2, 0, sizeof (struct grub_ext2_sblock),
                   (char *) &data->sblock);
-  if (grub_errno)
-    goto fail;
+  if (grub_errno != GRUB_ERR_NONE)
+    EXT2_DRIVER_MOUNT_FAIL(0);
 
   /* Make sure this is an ext2 filesystem.  */
   if (grub_le_to_cpu16 (data->sblock.magic) != EXT2_MAGIC)
-    goto fail;
+    EXT2_DRIVER_MOUNT_FAIL("not an ext2 filesystem");
   
+  /* Check the FS doesn't have feature bits enabled that we don't support. */
+  if (grub_le_to_cpu32 (data->sblock.feature_incompat)
+        & ~(EXT2_DRIVER_SUPPORTED_INCOMPAT | EXT2_DRIVER_IGNORED_INCOMPAT))
+    EXT2_DRIVER_MOUNT_FAIL("filesystem has unsupported incompatible features");
+    
+  
   data->disk = disk;
 
   data->diropen.data = data;
@@ -514,13 +567,15 @@
   data->inode = &data->diropen.inode;
 
   grub_ext2_read_inode (data, 2, data->inode);
-  if (grub_errno)
-    goto fail;
+  if (grub_errno != GRUB_ERR_NONE)
+    EXT2_DRIVER_MOUNT_FAIL(0);
   
   return data;
 
  fail:
-  grub_error (GRUB_ERR_BAD_FS, "not an ext2 filesystem");
+  /* Only call grub_error if the fail was _not_ caused by underlying errors.  */
+  if (local_error)
+    grub_error (GRUB_ERR_BAD_FS, local_error);
   grub_free (data);
   return 0;
 }

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