/*
   * High-level sync()-related operations
   */
  
  #include <linux/kernel.h>
  #include <linux/file.h>
  #include <linux/fs.h>
  #include <linux/slab.h>
  #include <linux/export.h>
  #include <linux/namei.h>
  #include <linux/sched.h>
  #include <linux/writeback.h>
  #include <linux/syscalls.h>
  #include <linux/linkage.h>
  #include <linux/pagemap.h>
  #include <linux/quotaops.h>
  #include <linux/backing-dev.h>
  #include "internal.h"
  
  #define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
  			SYNC_FILE_RANGE_WAIT_AFTER)
  
  /*
   * Do the filesystem syncing work. For simple filesystems
   * writeback_inodes_sb(sb) just dirties buffers with inodes so we have to
   * submit IO for these buffers via __sync_blockdev(). This also speeds up the
   * wait == 1 case since in that case write_inode() functions do
   * sync_dirty_buffer() and thus effectively write one block at a time.
   */
  static int __sync_filesystem(struct super_block *sb, int wait)
  {
  	if (wait)
  		sync_inodes_sb(sb);
  	else
  		writeback_inodes_sb(sb, WB_REASON_SYNC);
  
  	if (sb->s_op->sync_fs)
  		sb->s_op->sync_fs(sb, wait);
  	return __sync_blockdev(sb->s_bdev, wait);
  }
  
  /*
   * Write out and wait upon all dirty data associated with this
   * superblock.  Filesystem data as well as the underlying block
   * device.  Takes the superblock lock.
   */
  int sync_filesystem(struct super_block *sb)
  {
  	int ret;
  
  	/*
  	 * We need to be protected against the filesystem going from
  	 * r/o to r/w or vice versa.
  	 */
  	WARN_ON(!rwsem_is_locked(&sb->s_umount));
  
  	/*
  	 * No point in syncing out anything if the filesystem is read-only.
  	 */
  	if (sb->s_flags & MS_RDONLY)
  		return 0;
  
  	ret = __sync_filesystem(sb, 0);
  	if (ret < 0)
  		return ret;
  	return __sync_filesystem(sb, 1);
  }
  EXPORT_SYMBOL_GPL(sync_filesystem);
  
  static void sync_inodes_one_sb(struct super_block *sb, void *arg)
  {
  	if (!(sb->s_flags & MS_RDONLY))
  		sync_inodes_sb(sb);
  }
  
  static void sync_fs_one_sb(struct super_block *sb, void *arg)
  {
  	if (!(sb->s_flags & MS_RDONLY) && sb->s_op->sync_fs)
  		sb->s_op->sync_fs(sb, *(int *)arg);
  }
  
  static void fdatawrite_one_bdev(struct block_device *bdev, void *arg)
  {
  	filemap_fdatawrite(bdev->bd_inode->i_mapping);
  }
  
  static void fdatawait_one_bdev(struct block_device *bdev, void *arg)
  {
  	filemap_fdatawait(bdev->bd_inode->i_mapping);
  }
  
  /*
   * Sync everything. We start by waking flusher threads so that most of
   * writeback runs on all devices in parallel. Then we sync all inodes reliably
   * which effectively also waits for all flusher threads to finish doing
   * writeback. At this point all data is on disk so metadata should be stable
   * and we tell filesystems to sync their metadata via ->sync_fs() calls.
   * Finally, we writeout all block devices because some filesystems (e.g. ext2)
   * just write metadata (such as inodes or bitmaps) to block device page cache
   * and do not sync it on their own in ->sync_fs().
   */
  SYSCALL_DEFINE0(sync)
  {
  	int nowait = 0, wait = 1;
  
  	wakeup_flusher_threads(0, WB_REASON_SYNC);
  	iterate_supers(sync_inodes_one_sb, NULL);
  	iterate_supers(sync_fs_one_sb, &nowait);
  	iterate_supers(sync_fs_one_sb, &wait);
  	iterate_bdevs(fdatawrite_one_bdev, NULL);
  	iterate_bdevs(fdatawait_one_bdev, NULL);
  	if (unlikely(laptop_mode))
  		laptop_sync_completion();
  	return 0;
  }
  
  static void do_sync_work(struct work_struct *work)
  {
  	int nowait = 0;
  
  	/*
  	 * Sync twice to reduce the possibility we skipped some inodes / pages
  	 * because they were temporarily locked
  	 */
  	iterate_supers(sync_inodes_one_sb, &nowait);
  	iterate_supers(sync_fs_one_sb, &nowait);
  	iterate_bdevs(fdatawrite_one_bdev, NULL);
  	iterate_supers(sync_inodes_one_sb, &nowait);
  	iterate_supers(sync_fs_one_sb, &nowait);
  	iterate_bdevs(fdatawrite_one_bdev, NULL);
  	printk("Emergency Sync complete
  ");
  	kfree(work);
  }
  
  void emergency_sync(void)
  {
  	struct work_struct *work;
  
  	work = kmalloc(sizeof(*work), GFP_ATOMIC);
  	if (work) {
  		INIT_WORK(work, do_sync_work);
  		schedule_work(work);
  	}
  }
  
  /*
   * sync a single super
   */
  SYSCALL_DEFINE1(syncfs, int, fd)
  {
  	struct fd f = fdget(fd);
  	struct super_block *sb;
  	int ret;
  
  	if (!f.file)
  		return -EBADF;
  	sb = f.file->f_dentry->d_sb;
  
  	down_read(&sb->s_umount);
  	ret = sync_filesystem(sb);
  	up_read(&sb->s_umount);
  
  	fdput(f);
  	return ret;
  }
  
  /**
   * vfs_fsync_range - helper to sync a range of data & metadata to disk
   * @file:		file to sync
   * @start:		offset in bytes of the beginning of data range to sync
   * @end:		offset in bytes of the end of data range (inclusive)
   * @datasync:		perform only datasync
   *
   * Write back data in range @start..@end and metadata for @file to disk.  If
   * @datasync is set only metadata needed to access modified file data is
   * written.
   */
  int vfs_fsync_range(struct file *file, loff_t start, loff_t end, int datasync)
  {
  	if (!file->f_op->fsync)
  		return -EINVAL;
  	return file->f_op->fsync(file, start, end, datasync);
  }
  EXPORT_SYMBOL(vfs_fsync_range);
  
  /**
   * vfs_fsync - perform a fsync or fdatasync on a file
   * @file:		file to sync
   * @datasync:		only perform a fdatasync operation
   *
   * Write back data and metadata for @file to disk.  If @datasync is
   * set only metadata needed to access modified file data is written.
   */
  int vfs_fsync(struct file *file, int datasync)
  {
  	return vfs_fsync_range(file, 0, LLONG_MAX, datasync);
  }
  EXPORT_SYMBOL(vfs_fsync);
  
  static int do_fsync(unsigned int fd, int datasync)
  {
  	struct fd f = fdget(fd);
  	int ret = -EBADF;
  
  	if (f.file) {
  		ret = vfs_fsync(f.file, datasync);
  		fdput(f);
  	}
  	return ret;
  }
  
  SYSCALL_DEFINE1(fsync, unsigned int, fd)
  {
  	return do_fsync(fd, 0);
  }
  
  SYSCALL_DEFINE1(fdatasync, unsigned int, fd)
  {
  	return do_fsync(fd, 1);
  }
  
  /*
   * sys_sync_file_range() permits finely controlled syncing over a segment of
   * a file in the range offset .. (offset+nbytes-1) inclusive.  If nbytes is
   * zero then sys_sync_file_range() will operate from offset out to EOF.
   *
   * The flag bits are:
   *
   * SYNC_FILE_RANGE_WAIT_BEFORE: wait upon writeout of all pages in the range
   * before performing the write.
   *
   * SYNC_FILE_RANGE_WRITE: initiate writeout of all those dirty pages in the
   * range which are not presently under writeback. Note that this may block for
   * significant periods due to exhaustion of disk request structures.
   *
   * SYNC_FILE_RANGE_WAIT_AFTER: wait upon writeout of all pages in the range
   * after performing the write.
   *
   * Useful combinations of the flag bits are:
   *
   * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE: ensures that all pages
   * in the range which were dirty on entry to sys_sync_file_range() are placed
   * under writeout.  This is a start-write-for-data-integrity operation.
   *
   * SYNC_FILE_RANGE_WRITE: start writeout of all dirty pages in the range which
   * are not presently under writeout.  This is an asynchronous flush-to-disk
   * operation.  Not suitable for data integrity operations.
   *
   * SYNC_FILE_RANGE_WAIT_BEFORE (or SYNC_FILE_RANGE_WAIT_AFTER): wait for
   * completion of writeout of all pages in the range.  This will be used after an
   * earlier SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE operation to wait
   * for that operation to complete and to return the result.
   *
   * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER:
   * a traditional sync() operation.  This is a write-for-data-integrity operation
   * which will ensure that all pages in the range which were dirty on entry to
   * sys_sync_file_range() are committed to disk.
   *
   *
   * SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any
   * I/O errors or ENOSPC conditions and will return those to the caller, after
   * clearing the EIO and ENOSPC flags in the address_space.
   *
   * It should be noted that none of these operations write out the file's
   * metadata.  So unless the application is strictly performing overwrites of
   * already-instantiated disk blocks, there are no guarantees here that the data
   * will be available after a crash.
   */
  SYSCALL_DEFINE4(sync_file_range, int, fd, loff_t, offset, loff_t, nbytes,
  				unsigned int, flags)
  {
  	int ret;
  	struct fd f;
  	struct address_space *mapping;
  	loff_t endbyte;			/* inclusive */
  	umode_t i_mode;
  
  	ret = -EINVAL;
  	if (flags & ~VALID_FLAGS)
  		goto out;
  
  	endbyte = offset + nbytes;
  
  	if ((s64)offset < 0)
  		goto out;
  	if ((s64)endbyte < 0)
  		goto out;
  	if (endbyte < offset)
  		goto out;
  
  	if (sizeof(pgoff_t) == 4) {
  		if (offset >= (0x100000000ULL << PAGE_CACHE_SHIFT)) {
  			/*
  			 * The range starts outside a 32 bit machine's
  			 * pagecache addressing capabilities.  Let it "succeed"
  			 */
  			ret = 0;
  			goto out;
  		}
  		if (endbyte >= (0x100000000ULL << PAGE_CACHE_SHIFT)) {
  			/*
  			 * Out to EOF
  			 */
  			nbytes = 0;
  		}
  	}
  
  	if (nbytes == 0)
  		endbyte = LLONG_MAX;
  	else
  		endbyte--;		/* inclusive */
  
  	ret = -EBADF;
  	f = fdget(fd);
  	if (!f.file)
  		goto out;
  
  	i_mode = file_inode(f.file)->i_mode;
  	ret = -ESPIPE;
  	if (!S_ISREG(i_mode) && !S_ISBLK(i_mode) && !S_ISDIR(i_mode) &&
  			!S_ISLNK(i_mode))
  		goto out_put;
  
  	mapping = f.file->f_mapping;
  	if (!mapping) {
  		ret = -EINVAL;
  		goto out_put;
  	}
  
  	ret = 0;
  	if (flags & SYNC_FILE_RANGE_WAIT_BEFORE) {
  		ret = filemap_fdatawait_range(mapping, offset, endbyte);
  		if (ret < 0)
  			goto out_put;
  	}
  
  	if (flags & SYNC_FILE_RANGE_WRITE) {
  		ret = filemap_fdatawrite_range(mapping, offset, endbyte);
  		if (ret < 0)
  			goto out_put;
  	}
  
  	if (flags & SYNC_FILE_RANGE_WAIT_AFTER)
  		ret = filemap_fdatawait_range(mapping, offset, endbyte);
  
  out_put:
  	fdput(f);
  out:
  	return ret;
  }
  
  /* It would be nice if people remember that not all the world's an i386
     when they introduce new system calls */
  SYSCALL_DEFINE4(sync_file_range2, int, fd, unsigned int, flags,
  				 loff_t, offset, loff_t, nbytes)
  {
  	return sys_sync_file_range(fd, offset, nbytes, flags);
  }