freeze_bdev
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## 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.

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