+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
File management in the Linux kernel
------------------------------------
+===================================
This document describes how locking for files (struct file)
and file descriptor table (struct files) works.
the fdtable structure -
1. All references to the fdtable must be done through
- the files_fdtable() macro :
+ the files_fdtable() macro::
struct fdtable *fdt;
4. To look up the file structure given an fd, a reader
must use either fcheck() or fcheck_files() APIs. These
take care of barrier requirements due to lock-free lookup.
- An example :
+
+ An example::
struct file *file;
of the fd (fget()/fget_light()) are lock-free, it is possible
that look-up may race with the last put() operation on the
file structure. This is avoided using atomic_long_inc_not_zero()
- on ->f_count :
+ on ->f_count::
rcu_read_lock();
file = fcheck_files(files, fd);
holding files->file_lock. If ->file_lock is dropped, then
another thread expand the files thereby creating a new
fdtable and making the earlier fdtable pointer stale.
- For example :
+
+ For example::
spin_lock(&files->file_lock);
fd = locate_fd(files, file, start);