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Message-ID: <20110417020141.GB3806@thunk.org>
Date: Sat, 16 Apr 2011 22:01:41 -0400
From: Ted Ts'o <tytso@....edu>
To: Milton Miller <miltonm@....com>
Cc: Mark Lord <kernel@...savvy.com>, ricwheeler@...il.com,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: register ext2 and ext3 alias after ext4
On Thu, Apr 14, 2011 at 10:30:07AM -0500, Milton Miller wrote:
> The intent of CONFIG_EXT4_USE_FOR_EXT23 is to provide an alias so
> that the ext4 module is sufficient even if user space calls out ext2.
> However, it currently registers the alias names before registering ext4.
> This means they show up first in /proc/filesystems and ext3 and ext4
> formatted file systems show up in the mount list as ext4.
Note this is only true for the root file system.
>
> Register the filesystem aliases after ext4 so they show as ext4 until the
> filesystems is filtered. This will avoid users or tools configuring a
> kernel with just ext2 and wondering why there system broke. Also register
> in the same order as listed in fs/Makefile.
>
> Signed-off-by: Milton Miller <miltonm@....com>
This is actually the better way to fix Mark's complaint, as it
provides the correct behaviour if someone tries explicitly mounting an
ext4 file system via "mount -t ext2 /dev/sda". It also provides a
better explanation of what happens when CONFIG_EXT4_USE_EXT23 is
enabled and ext2 and ext3 are deconfigured, and the user has an ext2
or ext3 root file system. Now they will something like this:
EXT4-fs (sda): mounting ext2 file system using the ext4 subsystem
EXT4-fs (sda): mounted filesystem without journal. Opts: (null)
which makes clearer what is going on.
- Ted
>From 5a5baedb6306edb9effc86add73e9522e2a70532 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@....edu>
Date: Sat, 16 Apr 2011 21:31:57 -0400
Subject: [PATCH] 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@....edu>
---
fs/ext4/ext4.h | 15 +++++++++++
fs/ext4/super.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++------
2 files changed, 79 insertions(+), 8 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 4daaf2b..076c5d2 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1351,6 +1351,21 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
#define EXT4_FEATURE_INCOMPAT_EA_INODE 0x0400 /* EA in inode */
#define EXT4_FEATURE_INCOMPAT_DIRDATA 0x1000 /* data in dirent */
+#define EXT2_FEATURE_COMPAT_SUPP EXT4_FEATURE_COMPAT_EXT_ATTR
+#define EXT2_FEATURE_INCOMPAT_SUPP (EXT4_FEATURE_INCOMPAT_FILETYPE| \
+ EXT4_FEATURE_INCOMPAT_META_BG)
+#define EXT2_FEATURE_RO_COMPAT_SUPP (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
+ EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
+ EXT4_FEATURE_RO_COMPAT_BTREE_DIR)
+
+#define EXT3_FEATURE_COMPAT_SUPP EXT4_FEATURE_COMPAT_EXT_ATTR
+#define EXT3_FEATURE_INCOMPAT_SUPP (EXT4_FEATURE_INCOMPAT_FILETYPE| \
+ EXT4_FEATURE_INCOMPAT_RECOVER| \
+ EXT4_FEATURE_INCOMPAT_META_BG)
+#define EXT3_FEATURE_RO_COMPAT_SUPP (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
+ EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
+ EXT4_FEATURE_RO_COMPAT_BTREE_DIR)
+
#define EXT4_FEATURE_COMPAT_SUPP EXT2_FEATURE_COMPAT_EXT_ATTR
#define EXT4_FEATURE_INCOMPAT_SUPP (EXT4_FEATURE_INCOMPAT_FILETYPE| \
EXT4_FEATURE_INCOMPAT_RECOVER| \
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 8553dfb..bb2d660 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -75,11 +75,27 @@ static void ext4_write_super(struct super_block *sb);
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 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
"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 @@ static struct dentry *ext4_mount(struct file_system_type *fs_type, int flags,
}
#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 @@ static inline void unregister_as_ext2(void)
{
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 @@ static inline void unregister_as_ext3(void)
{
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 = {
--
1.7.3.1
--
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