From b62e88af6a1be97b224a3e5c1fea43fa173567ea Mon Sep 17 00:00:00 2001 From: Andreas Dilger Date: Thu, 31 May 2007 12:25:46 -0400 Subject: [PATCH] Reserve superblock fields for multiple mount protection feature There have been reported instances of a filesystem having been mounted at 2 places at the same time causing a lot of damage to the filesystem. This patch reserves superblock fields and an INCOMPAT flag for adding multiple mount protection(MMP) support within the ext4 filesystem itself. The superblock will have a block number (s_mmp_block) which will hold a MMP structure which has a sequence number which will be periodically updated every 5 seconds by a mounted filesystem. Whenever a filesystem will be mounted it will wait for s_mmp_interval seconds to make sure that the MMP sequence does not change. To further make sure, we write a random sequence number into the MMP block and wait for another s_mmp_interval secs. If the sequence no. doesn't change then the mount will succeed. In case of failure, the nodename, bdevname and the time at which the MMP block was last updated will be displayed. tune2fs can be used to set s_mmp_interval as desired. Signed-off-by: Andreas Dilger Signed-off-by: Kalpak Shah --- lib/ext2fs/ChangeLog | 5 +++++ lib/ext2fs/ext2_fs.h | 31 +++++++++++++++++++++++++++++-- 2 files changed, 34 insertions(+), 2 deletions(-) diff --git a/lib/ext2fs/ChangeLog b/lib/ext2fs/ChangeLog index def7b2a..3f53df7 100644 --- a/lib/ext2fs/ChangeLog +++ b/lib/ext2fs/ChangeLog @@ -1,3 +1,8 @@ +2007-05-31 Kalpak Shah + + * ext2_fs.h: Reserve superblock fields and INCOMPAT feature flag + for multiple mount protection protection. + 2007-05-23 Theodore Tso * icount.c (ext2fs_icount_fetch, ext2fs_icount_increment, setup): diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h index 98f34fc..81bd190 100644 --- a/lib/ext2fs/ext2_fs.h +++ b/lib/ext2fs/ext2_fs.h @@ -574,8 +574,9 @@ struct ext2_super_block { __u16 s_want_extra_isize; /* New inodes should reserve # bytes */ __u32 s_flags; /* Miscellaneous flags */ __u16 s_raid_stride; /* RAID stride */ - __u16 s_pad; /* Padding */ - __u32 s_reserved[166]; /* Padding to the end of the block */ + __u16 s_mmp_interval; /* # seconds to wait in MMP checking */ + __u64 s_mmp_block; /* Block for multi-mount protection */ + __u32 s_reserved[164]; /* Padding to the end of the block */ }; /* @@ -637,6 +638,7 @@ struct ext2_super_block { #define EXT2_FEATURE_INCOMPAT_META_BG 0x0010 #define EXT3_FEATURE_INCOMPAT_EXTENTS 0x0040 #define EXT4_FEATURE_INCOMPAT_64BIT 0x0080 +#define EXT4_FEATURE_INCOMPAT_MMP 0x0100 #define EXT2_FEATURE_COMPAT_SUPP 0 @@ -715,4 +717,29 @@ struct ext2_dir_entry_2 { #define EXT2_DIR_REC_LEN(name_len) (((name_len) + 8 + EXT2_DIR_ROUND) & \ ~EXT2_DIR_ROUND) +/* + * This structure will be used for multiple mount protection. It will be + * written into the block number saved in the s_mmp_block field in the + * superblock. + */ +#define EXT2_MMP_MAGIC 0x004D4D50 /* ASCII for MMP */ +#define EXT2_MMP_CLEAN 0xFF4D4D50 /* Value of mmp_seq for clean unmount */ +#define EXT2_MMP_FSCK_ON 0xE24D4D50 /* Value of mmp_seq when being fscked */ + +struct mmp_struct { + __u32 mmp_magic; + __u32 mmp_seq; + __u64 mmp_time; + char mmp_nodename[64]; + char mmp_bdevname[32]; + __u16 mmp_interval; + __u16 mmp_pad1; + __u32 mmp_pad2; +}; + +/* + * Interval in number of seconds to update the MMP sequence number. + */ +#define EXT2_MMP_DEF_INTERVAL 5 + #endif /* _LINUX_EXT2_FS_H */ -- 1.8.3.1