freeze_bdev (9) - Linux Manuals
freeze_bdev: - lock a filesystem and force it into a consistent state
freeze_bdev - - lock a filesystem and force it into a consistent state
struct super_block * freeze_bdev(struct block_device
- blockdevice to lock
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.