#include <linux/fs.h>
  #include <linux/random.h>
  #include <linux/buffer_head.h>
  #include <linux/utsname.h>
  #include <linux/kthread.h>
  
  #include "ext4.h"

  /* Checksumming functions */

  static __le32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)

  {
  	struct ext4_sb_info *sbi = EXT4_SB(sb);
  	int offset = offsetof(struct mmp_struct, mmp_checksum);
  	__u32 csum;
  
  	csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);
  
  	return cpu_to_le32(csum);
  }

  static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)

  {

  	if (!ext4_has_metadata_csum(sb))

  		return 1;
  
  	return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
  }

  static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)

  {

  	if (!ext4_has_metadata_csum(sb))

  		return;
  
  	mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
  }

  /*
   * Write the MMP block using WRITE_SYNC to try to get the block on-disk
   * faster.
   */

  static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)

  {

  	struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);

  	/*
  	 * We protect against freezing so that we don't create dirty buffers
  	 * on frozen filesystem.
  	 */
  	sb_start_write(sb);

  	ext4_mmp_csum_set(sb, mmp);

  	mark_buffer_dirty(bh);
  	lock_buffer(bh);
  	bh->b_end_io = end_buffer_write_sync;
  	get_bh(bh);

  	submit_bh(REQ_OP_WRITE, WRITE_SYNC | REQ_META | REQ_PRIO, bh);

  	wait_on_buffer(bh);

  	sb_end_write(sb);

  	if (unlikely(!buffer_uptodate(bh)))
  		return 1;
  
  	return 0;
  }
  
  /*
   * Read the MMP block. It _must_ be read from disk and hence we clear the
   * uptodate flag on the buffer.
   */
  static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
  			  ext4_fsblk_t mmp_block)
  {
  	struct mmp_struct *mmp;

  	int ret;

  
  	if (*bh)
  		clear_buffer_uptodate(*bh);
  
  	/* This would be sb_bread(sb, mmp_block), except we need to be sure
  	 * that the MD RAID device cache has been bypassed, and that the read
  	 * is not blocked in the elevator. */

  	if (!*bh) {

  		*bh = sb_getblk(sb, mmp_block);

  		if (!*bh) {
  			ret = -ENOMEM;
  			goto warn_exit;

  		}
  	}

  
  	get_bh(*bh);
  	lock_buffer(*bh);
  	(*bh)->b_end_io = end_buffer_read_sync;

  	submit_bh(REQ_OP_READ, READ_SYNC | REQ_META | REQ_PRIO, *bh);

  	wait_on_buffer(*bh);
  	if (!buffer_uptodate(*bh)) {

  		ret = -EIO;
  		goto warn_exit;

  	}

  	mmp = (struct mmp_struct *)((*bh)->b_data);

  	if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {

  		ret = -EFSCORRUPTED;

  		goto warn_exit;
  	}
  	if (!ext4_mmp_csum_verify(sb, mmp)) {

  		ret = -EFSBADCRC;

  		goto warn_exit;
  	}
  	return 0;

  warn_exit:

  	brelse(*bh);
  	*bh = NULL;

  	ext4_warning(sb, "Error %d while reading MMP block %llu",
  		     ret, mmp_block);
  	return ret;

  }
  
  /*
   * Dump as much information as possible to help the admin.
   */
  void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
  		    const char *function, unsigned int line, const char *msg)
  {

  	__ext4_warning(sb, function, line, "%s", msg);

  	__ext4_warning(sb, function, line,
  		       "MMP failure info: last update time: %llu, last update "

  		       "node: %s, last update device: %s",

  		       (long long unsigned int) le64_to_cpu(mmp->mmp_time),
  		       mmp->mmp_nodename, mmp->mmp_bdevname);
  }
  
  /*
   * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
   */
  static int kmmpd(void *data)
  {
  	struct super_block *sb = ((struct mmpd_data *) data)->sb;
  	struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
  	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
  	struct mmp_struct *mmp;
  	ext4_fsblk_t mmp_block;
  	u32 seq = 0;
  	unsigned long failed_writes = 0;
  	int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
  	unsigned mmp_check_interval;
  	unsigned long last_update_time;
  	unsigned long diff;
  	int retval;
  
  	mmp_block = le64_to_cpu(es->s_mmp_block);
  	mmp = (struct mmp_struct *)(bh->b_data);
  	mmp->mmp_time = cpu_to_le64(get_seconds());
  	/*
  	 * Start with the higher mmp_check_interval and reduce it if
  	 * the MMP block is being updated on time.
  	 */
  	mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
  				 EXT4_MMP_MIN_CHECK_INTERVAL);
  	mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
  	bdevname(bh->b_bdev, mmp->mmp_bdevname);

  	memcpy(mmp->mmp_nodename, init_utsname()->nodename,

  	       sizeof(mmp->mmp_nodename));
  
  	while (!kthread_should_stop()) {
  		if (++seq > EXT4_MMP_SEQ_MAX)
  			seq = 1;
  
  		mmp->mmp_seq = cpu_to_le32(seq);
  		mmp->mmp_time = cpu_to_le64(get_seconds());
  		last_update_time = jiffies;

  		retval = write_mmp_block(sb, bh);

  		/*
  		 * Don't spew too many error messages. Print one every
  		 * (s_mmp_update_interval * 60) seconds.
  		 */

  		if (retval) {
  			if ((failed_writes % 60) == 0)
  				ext4_error(sb, "Error writing to MMP block");

  			failed_writes++;
  		}
  
  		if (!(le32_to_cpu(es->s_feature_incompat) &
  		    EXT4_FEATURE_INCOMPAT_MMP)) {
  			ext4_warning(sb, "kmmpd being stopped since MMP feature"
  				     " has been disabled.");

  			goto exit_thread;

  		}
  
  		if (sb->s_flags & MS_RDONLY) {
  			ext4_warning(sb, "kmmpd being stopped since filesystem "
  				     "has been remounted as readonly.");

  			goto exit_thread;

  		}
  
  		diff = jiffies - last_update_time;
  		if (diff < mmp_update_interval * HZ)
  			schedule_timeout_interruptible(mmp_update_interval *
  						       HZ - diff);
  
  		/*
  		 * We need to make sure that more than mmp_check_interval
  		 * seconds have not passed since writing. If that has happened
  		 * we need to check if the MMP block is as we left it.
  		 */
  		diff = jiffies - last_update_time;
  		if (diff > mmp_check_interval * HZ) {
  			struct buffer_head *bh_check = NULL;
  			struct mmp_struct *mmp_check;
  
  			retval = read_mmp_block(sb, &bh_check, mmp_block);
  			if (retval) {
  				ext4_error(sb, "error reading MMP data: %d",
  					   retval);

  				goto exit_thread;

  			}
  
  			mmp_check = (struct mmp_struct *)(bh_check->b_data);
  			if (mmp->mmp_seq != mmp_check->mmp_seq ||
  			    memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
  				   sizeof(mmp->mmp_nodename))) {
  				dump_mmp_msg(sb, mmp_check,
  					     "Error while updating MMP info. "
  					     "The filesystem seems to have been"
  					     " multiply mounted.");
  				ext4_error(sb, "abort");

  				put_bh(bh_check);
  				retval = -EBUSY;
  				goto exit_thread;

  			}
  			put_bh(bh_check);
  		}
  
  		 /*
  		 * Adjust the mmp_check_interval depending on how much time
  		 * it took for the MMP block to be written.
  		 */
  		mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
  					     EXT4_MMP_MAX_CHECK_INTERVAL),
  					 EXT4_MMP_MIN_CHECK_INTERVAL);
  		mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
  	}
  
  	/*
  	 * Unmount seems to be clean.
  	 */
  	mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
  	mmp->mmp_time = cpu_to_le64(get_seconds());

  	retval = write_mmp_block(sb, bh);

  exit_thread:
  	EXT4_SB(sb)->s_mmp_tsk = NULL;

  	kfree(data);
  	brelse(bh);
  	return retval;
  }
  
  /*
   * Get a random new sequence number but make sure it is not greater than
   * EXT4_MMP_SEQ_MAX.
   */
  static unsigned int mmp_new_seq(void)
  {
  	u32 new_seq;
  
  	do {

  		new_seq = prandom_u32();

  	} while (new_seq > EXT4_MMP_SEQ_MAX);
  
  	return new_seq;
  }
  
  /*
   * Protect the filesystem from being mounted more than once.
   */
  int ext4_multi_mount_protect(struct super_block *sb,
  				    ext4_fsblk_t mmp_block)
  {
  	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
  	struct buffer_head *bh = NULL;
  	struct mmp_struct *mmp = NULL;
  	struct mmpd_data *mmpd_data;
  	u32 seq;
  	unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
  	unsigned int wait_time = 0;
  	int retval;
  
  	if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
  	    mmp_block >= ext4_blocks_count(es)) {
  		ext4_warning(sb, "Invalid MMP block in superblock");
  		goto failed;
  	}
  
  	retval = read_mmp_block(sb, &bh, mmp_block);
  	if (retval)
  		goto failed;
  
  	mmp = (struct mmp_struct *)(bh->b_data);
  
  	if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
  		mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
  
  	/*
  	 * If check_interval in MMP block is larger, use that instead of
  	 * update_interval from the superblock.
  	 */

  	if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
  		mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);

  
  	seq = le32_to_cpu(mmp->mmp_seq);
  	if (seq == EXT4_MMP_SEQ_CLEAN)
  		goto skip;
  
  	if (seq == EXT4_MMP_SEQ_FSCK) {
  		dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
  		goto failed;
  	}
  
  	wait_time = min(mmp_check_interval * 2 + 1,
  			mmp_check_interval + 60);
  
  	/* Print MMP interval if more than 20 secs. */
  	if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
  		ext4_warning(sb, "MMP interval %u higher than expected, please"
  			     " wait.
  ", wait_time * 2);
  
  	if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
  		ext4_warning(sb, "MMP startup interrupted, failing mount
  ");
  		goto failed;
  	}
  
  	retval = read_mmp_block(sb, &bh, mmp_block);
  	if (retval)
  		goto failed;
  	mmp = (struct mmp_struct *)(bh->b_data);
  	if (seq != le32_to_cpu(mmp->mmp_seq)) {
  		dump_mmp_msg(sb, mmp,
  			     "Device is already active on another node.");
  		goto failed;
  	}
  
  skip:
  	/*
  	 * write a new random sequence number.
  	 */

  	seq = mmp_new_seq();
  	mmp->mmp_seq = cpu_to_le32(seq);

  	retval = write_mmp_block(sb, bh);

  	if (retval)
  		goto failed;
  
  	/*
  	 * wait for MMP interval and check mmp_seq.
  	 */
  	if (schedule_timeout_interruptible(HZ * wait_time) != 0) {

  		ext4_warning(sb, "MMP startup interrupted, failing mount");

  		goto failed;
  	}
  
  	retval = read_mmp_block(sb, &bh, mmp_block);
  	if (retval)
  		goto failed;
  	mmp = (struct mmp_struct *)(bh->b_data);
  	if (seq != le32_to_cpu(mmp->mmp_seq)) {
  		dump_mmp_msg(sb, mmp,
  			     "Device is already active on another node.");
  		goto failed;
  	}
  
  	mmpd_data = kmalloc(sizeof(struct mmpd_data), GFP_KERNEL);
  	if (!mmpd_data) {
  		ext4_warning(sb, "not enough memory for mmpd_data");
  		goto failed;
  	}
  	mmpd_data->sb = sb;
  	mmpd_data->bh = bh;
  
  	/*
  	 * Start a kernel thread to update the MMP block periodically.
  	 */
  	EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
  					     bdevname(bh->b_bdev,
  						      mmp->mmp_bdevname));
  	if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
  		EXT4_SB(sb)->s_mmp_tsk = NULL;
  		kfree(mmpd_data);
  		ext4_warning(sb, "Unable to create kmmpd thread for %s.",
  			     sb->s_id);
  		goto failed;
  	}
  
  	return 0;
  
  failed:
  	brelse(bh);
  	return 1;
  }