centos man page for freeze_bdev

FREEZE_BDEV(9)							   The Linux VFS						    FREEZE_BDEV(9)

NAME
       freeze_bdev - - lock a filesystem and force it into a consistent state

SYNOPSIS
       struct super_block * freeze_bdev(struct block_device * bdev);

ARGUMENTS
       bdev
	   blockdevice to lock

DESCRIPTION
       If a superblock is found on this device, we take the s_umount semaphore on it to make sure nobody unmounts until the snapshot creation is
       done. The reference counter (bd_fsfreeze_count) guarantees that only the last unfreeze process can unfreeze the frozen filesystem actually
       when multiple freeze requests arrive simultaneously. It counts up in freeze_bdev and count down in thaw_bdev. When it becomes 0, thaw_bdev
       will unfreeze actually.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							    FREEZE_BDEV(9)