From: Ted Ts'o Subject: Re: [PATCH] ext4: register ext2 and ext3 alias after ext4 Date: Sat, 16 Apr 2011 22:01:41 -0400 Message-ID: <20110417020141.GB3806@thunk.org> References: <4DA48AF4.5080803@teksavvy.com> <20110413004938.GE3682@thunk.org> <4DA5ADA6.5060301@teksavvy.com> <5A35771F-49B6-491E-B012-DBE68907E382@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mark Lord , ricwheeler@gmail.com, linux-ext4@vger.kernel.org To: Milton Miller Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:46021 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751364Ab1DQCBq (ORCPT ); Sat, 16 Apr 2011 22:01:46 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 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 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" --- 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