ext4: add support for multiple mount protection
Prevent an ext4 filesystem from being mounted multiple times.
A sequence number is stored on disk and is periodically updated (every 5
seconds by default) by a mounted filesystem.
At mount time, we now wait for s_mmp_update_interval seconds to make sure
that the MMP sequence does not change.
In case of failure, the nodename, bdevname and the time at which the MMP
block was last updated is displayed.
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 65fe1dc..c0c56c9 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1028,7 +1028,7 @@
__le16 s_want_extra_isize; /* New inodes should reserve # bytes */
__le32 s_flags; /* Miscellaneous flags */
__le16 s_raid_stride; /* RAID stride */
- __le16 s_mmp_interval; /* # seconds to wait in MMP checking */
+ __le16 s_mmp_update_interval; /* # seconds to wait in MMP checking */
__le64 s_mmp_block; /* Block for multi-mount protection */
__le32 s_raid_stripe_width; /* blocks on all data disks (N*stride)*/
__u8 s_log_groups_per_flex; /* FLEX_BG group size */
@@ -1204,6 +1204,9 @@
struct ext4_li_request *s_li_request;
/* Wait multiplier for lazy initialization thread */
unsigned int s_li_wait_mult;
+
+ /* Kernel thread for multiple mount protection */
+ struct task_struct *s_mmp_tsk;
};
static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
@@ -1375,7 +1378,8 @@
EXT4_FEATURE_INCOMPAT_META_BG| \
EXT4_FEATURE_INCOMPAT_EXTENTS| \
EXT4_FEATURE_INCOMPAT_64BIT| \
- EXT4_FEATURE_INCOMPAT_FLEX_BG)
+ EXT4_FEATURE_INCOMPAT_FLEX_BG| \
+ EXT4_FEATURE_INCOMPAT_MMP)
#define EXT4_FEATURE_RO_COMPAT_SUPP (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \
@@ -1627,6 +1631,67 @@
};
/*
+ * 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. Programs that check MMP should assume that if
+ * SEQ_FSCK (or any unknown code above SEQ_MAX) is present then it is NOT safe
+ * to use the filesystem, regardless of how old the timestamp is.
+ */
+#define EXT4_MMP_MAGIC 0x004D4D50U /* ASCII for MMP */
+#define EXT4_MMP_SEQ_CLEAN 0xFF4D4D50U /* mmp_seq value for clean unmount */
+#define EXT4_MMP_SEQ_FSCK 0xE24D4D50U /* mmp_seq value when being fscked */
+#define EXT4_MMP_SEQ_MAX 0xE24D4D4FU /* maximum valid mmp_seq value */
+
+struct mmp_struct {
+ __le32 mmp_magic; /* Magic number for MMP */
+ __le32 mmp_seq; /* Sequence no. updated periodically */
+
+ /*
+ * mmp_time, mmp_nodename & mmp_bdevname are only used for information
+ * purposes and do not affect the correctness of the algorithm
+ */
+ __le64 mmp_time; /* Time last updated */
+ char mmp_nodename[64]; /* Node which last updated MMP block */
+ char mmp_bdevname[32]; /* Bdev which last updated MMP block */
+
+ /*
+ * mmp_check_interval is used to verify if the MMP block has been
+ * updated on the block device. The value is updated based on the
+ * maximum time to write the MMP block during an update cycle.
+ */
+ __le16 mmp_check_interval;
+
+ __le16 mmp_pad1;
+ __le32 mmp_pad2[227];
+};
+
+/* arguments passed to the mmp thread */
+struct mmpd_data {
+ struct buffer_head *bh; /* bh from initial read_mmp_block() */
+ struct super_block *sb; /* super block of the fs */
+};
+
+/*
+ * Check interval multiplier
+ * The MMP block is written every update interval and initially checked every
+ * update interval x the multiplier (the value is then adapted based on the
+ * write latency). The reason is that writes can be delayed under load and we
+ * don't want readers to incorrectly assume that the filesystem is no longer
+ * in use.
+ */
+#define EXT4_MMP_CHECK_MULT 2UL
+
+/*
+ * Minimum interval for MMP checking in seconds.
+ */
+#define EXT4_MMP_MIN_CHECK_INTERVAL 5UL
+
+/*
+ * Maximum interval for MMP checking in seconds.
+ */
+#define EXT4_MMP_MAX_CHECK_INTERVAL 300UL
+
+/*
* Function prototypes
*/
@@ -1800,6 +1865,10 @@
__LINE__, ## message)
extern void ext4_msg(struct super_block *, const char *, const char *, ...)
__attribute__ ((format (printf, 3, 4)));
+extern void __dump_mmp_msg(struct super_block *, struct mmp_struct *mmp,
+ const char *, unsigned int, const char *);
+#define dump_mmp_msg(sb, mmp, msg) __dump_mmp_msg(sb, mmp, __func__, \
+ __LINE__, msg)
extern void __ext4_grp_locked_error(const char *, unsigned int, \
struct super_block *, ext4_group_t, \
unsigned long, ext4_fsblk_t, \
@@ -2104,6 +2173,9 @@
int len,
struct writeback_control *wbc);
+/* mmp.c */
+extern int ext4_multi_mount_protect(struct super_block *, ext4_fsblk_t);
+
/* BH_Uninit flag: blocks are allocated but uninitialized on disk */
enum ext4_state_bits {
BH_Uninit /* blocks are allocated but uninitialized on disk */