SB_START_WRITE(9)                         The Linux VFS                         SB_START_WRITE(9)



NAME
       sb_start_write - get write access to a superblock

SYNOPSIS
       void sb_start_write(struct super_block * sb);

ARGUMENTS
       sb
           the super we write to

DESCRIPTION
       When a process wants to write data or metadata to a file system (i.e. dirty a page or an
       inode), it should embed the operation in a sb_start_write - sb_end_write pair to get
       exclusion against file system freezing. This function increments number of writers
       preventing freezing. If the file system is already frozen, the function waits until the
       file system is thawed.

       Since freeze protection behaves as a lock, users have to preserve ordering of freeze
       protection and other filesystem locks. Generally, freeze protection should be the
       outermost lock. In particular, we have:

       sb_start_write -> i_mutex (write path, truncate, directory ops, ...) -> s_umount
       (freeze_super, thaw_super)

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