sb_start_write — get write access to a superblock
void sb_start_write ( | struct super_block * sb); |
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)