FREEZE_SUPER(9) The Linux VFS FREEZE_SUPER(9)NAMEfreeze_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.
COPYRIGHTKernel Hackers Manual 3.8. June 2014 FREEZE_SUPER(9)