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 2.6. May 2011 FREEZE_BDEV(9)