FREEZE_SUPER(9)                           The Linux VFS                           FREEZE_SUPER(9)



NAME
       freeze_super - lock the filesystem and force it into a consistent state

SYNOPSIS
       int freeze_super(struct super_block * sb);

ARGUMENTS
       sb
           the super to lock

DESCRIPTION
       Syncs the super to make sure the filesystem is consistent and calls the fs's freeze_fs.
       Subsequent calls to this without first thawing the fs will return -EBUSY.

       During this function, sb->s_writers.frozen goes through these values:

       SB_UNFROZEN: File system is normal, all writes progress as usual.

       SB_FREEZE_WRITE: The file system is in the process of being frozen. New writes should be
       blocked, though page faults are still allowed. We wait for all writes to complete and then
       proceed to the next stage.

       SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked but internal fs
       threads can still modify the filesystem (although they should not dirty new pages or
       inodes), writeback can run etc. After waiting for all running page faults we sync the
       filesystem which will clean all dirty pages and inodes (no new dirty pages or inodes can
       be created when sync is running).

       SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs modification are
       blocked (e.g. XFS preallocation truncation on inode reclaim). This is usually implemented
       by blocking new transactions for filesystems that have them and need this additional
       guard. After all internal writers are finished we call ->freeze_fs to finish filesystem
       freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is mostly auxiliary
       for filesystems to verify they do not modify frozen fs.

       sb->s_writers.frozen is protected by sb->s_umount.

COPYRIGHT
Kernel Hackers Manual 4.8.                 January 2017                           FREEZE_SUPER(9)