ext4: check for ext[23] file system features when mounting as ext[23]
Provide better emulation for ext[23] mode by enforcing that the file
system does not have any unsupported file system features as defined
by ext[23] when emulating the ext[23] file system driver when
CONFIG_EXT4_USE_FOR_EXT23 is defined.
This causes the file system type information in /proc/mounts to be
correct for the automatically mounted root file system. This also
means that "mount -t ext2 /dev/sda /mnt" will fail if /dev/sda
contains an ext3 or ext4 file system, just as one would expect if the
original ext2 file system driver were in use.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 8553dfb..cb22783 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -75,11 +75,27 @@
static int ext4_freeze(struct super_block *sb);
static struct dentry *ext4_mount(struct file_system_type *fs_type, int flags,
const char *dev_name, void *data);
+static inline int ext2_feature_set_ok(struct super_block *sb);
+static inline int ext3_feature_set_ok(struct super_block *sb);
static int ext4_feature_set_ok(struct super_block *sb, int readonly);
static void ext4_destroy_lazyinit_thread(void);
static void ext4_unregister_li_request(struct super_block *sb);
static void ext4_clear_request_list(void);
+#if !defined(CONFIG_EXT2_FS) && !defined(CONFIG_EXT2_FS_MODULE) && defined(CONFIG_EXT4_USE_FOR_EXT23)
+static struct file_system_type ext2_fs_type = {
+ .owner = THIS_MODULE,
+ .name = "ext2",
+ .mount = ext4_mount,
+ .kill_sb = kill_block_super,
+ .fs_flags = FS_REQUIRES_DEV,
+};
+#define IS_EXT2_SB(sb) ((sb)->s_bdev->bd_holder == &ext2_fs_type)
+#else
+#define IS_EXT2_SB(sb) (0)
+#endif
+
+
#if !defined(CONFIG_EXT3_FS) && !defined(CONFIG_EXT3_FS_MODULE) && defined(CONFIG_EXT4_USE_FOR_EXT23)
static struct file_system_type ext3_fs_type = {
.owner = THIS_MODULE,
@@ -3187,6 +3203,28 @@
"feature flags set on rev 0 fs, "
"running e2fsck is recommended");
+ if (IS_EXT2_SB(sb)) {
+ if (ext2_feature_set_ok(sb))
+ ext4_msg(sb, KERN_INFO, "mounting ext2 file system "
+ "using the ext4 subsystem");
+ else {
+ ext4_msg(sb, KERN_ERR, "couldn't mount as ext2 due "
+ "to feature incompatibilities");
+ goto failed_mount;
+ }
+ }
+
+ if (IS_EXT3_SB(sb)) {
+ if (ext3_feature_set_ok(sb))
+ ext4_msg(sb, KERN_INFO, "mounting ext3 file system "
+ "using the ext4 subsystem");
+ else {
+ ext4_msg(sb, KERN_ERR, "couldn't mount as ext3 due "
+ "to feature incompatibilities");
+ goto failed_mount;
+ }
+ }
+
/*
* Check feature flags regardless of the revision level, since we
* previously didn't change the revision level when setting the flags,
@@ -4772,14 +4810,6 @@
}
#if !defined(CONFIG_EXT2_FS) && !defined(CONFIG_EXT2_FS_MODULE) && defined(CONFIG_EXT4_USE_FOR_EXT23)
-static struct file_system_type ext2_fs_type = {
- .owner = THIS_MODULE,
- .name = "ext2",
- .mount = ext4_mount,
- .kill_sb = kill_block_super,
- .fs_flags = FS_REQUIRES_DEV,
-};
-
static inline void register_as_ext2(void)
{
int err = register_filesystem(&ext2_fs_type);
@@ -4792,10 +4822,22 @@
{
unregister_filesystem(&ext2_fs_type);
}
+
+static inline int ext2_feature_set_ok(struct super_block *sb)
+{
+ if (EXT4_HAS_INCOMPAT_FEATURE(sb, ~EXT2_FEATURE_INCOMPAT_SUPP))
+ return 0;
+ if (sb->s_flags & MS_RDONLY)
+ return 1;
+ if (EXT4_HAS_RO_COMPAT_FEATURE(sb, ~EXT2_FEATURE_RO_COMPAT_SUPP))
+ return 0;
+ return 1;
+}
MODULE_ALIAS("ext2");
#else
static inline void register_as_ext2(void) { }
static inline void unregister_as_ext2(void) { }
+static inline int ext2_feature_set_ok(struct super_block *sb) { return 0; }
#endif
#if !defined(CONFIG_EXT3_FS) && !defined(CONFIG_EXT3_FS_MODULE) && defined(CONFIG_EXT4_USE_FOR_EXT23)
@@ -4811,10 +4853,24 @@
{
unregister_filesystem(&ext3_fs_type);
}
+
+static inline int ext3_feature_set_ok(struct super_block *sb)
+{
+ if (EXT4_HAS_INCOMPAT_FEATURE(sb, ~EXT3_FEATURE_INCOMPAT_SUPP))
+ return 0;
+ if (!EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_HAS_JOURNAL))
+ return 0;
+ if (sb->s_flags & MS_RDONLY)
+ return 1;
+ if (EXT4_HAS_RO_COMPAT_FEATURE(sb, ~EXT3_FEATURE_RO_COMPAT_SUPP))
+ return 0;
+ return 1;
+}
MODULE_ALIAS("ext3");
#else
static inline void register_as_ext3(void) { }
static inline void unregister_as_ext3(void) { }
+static inline int ext3_feature_set_ok(struct super_block *sb) { return 0; }
#endif
static struct file_system_type ext4_fs_type = {
@@ -4898,8 +4954,8 @@
err = init_inodecache();
if (err)
goto out1;
- register_as_ext2();
register_as_ext3();
+ register_as_ext2();
err = register_filesystem(&ext4_fs_type);
if (err)
goto out;