filesystems/caching/cachefiles.rst

1 .. SPDX-License-Identifier: GPL-2.0
36 CacheFiles is a caching backend that's meant to use as a cache a directory on
39 CacheFiles uses a userspace daemon to do some of the cache management - such as
48 CacheFiles creates a misc character device - "/dev/cachefiles" - that is used
57 space if necessary - see the "Cache Culling" section.  This means it can be
70 	- dnotify.
72 	- extended attributes (xattrs).
74 	- openat() and friends.
76 	- bmap() support on files in the filesystem (FIBMAP ioctl).
78 	- The use of bmap() to detect a partial page at the end of the file.
98 	Specify the directory containing the root of the cache.  Mandatory.
101 	Specify a tag to FS-Cache to use in distinguishing multiple caches.
129 	/sbin/cachefilesd [-d]* [-s] [-n] [-f <configfile>]
133  ``-d``
137  ``-s``
140  ``-n``
143  ``-f <configfile>``
151 kernel module contains its own very cut-down path walking facility that ignores
175 anything else.  Culling is based on the access time of data objects.  Empty
213 The CacheFiles module will create two directories in the directory it was
219 The active cache objects all reside in the first directory.  The CacheFiles
223 The daemon uses dnotify to monitor the graveyard directory, and will delete
228 "J...".  Note that the "cache/" directory is itself a special index.
232 directory, data objects will have a file in the directory called "data" that
239 If an object has children, then it will be represented as a directory.
240 Immediately in the representative directory are a collection of directories
242 this directory, if possible, will be placed the representations of the child
247 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400
248 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...DB1ry
249 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...N22ry
250 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...FP1ry
256 inside the last directory.  The names of the intermediate directories will have
267 "base-64" encode ones that aren't directly suitable.  The two versions of
299 security context that is not appropriate for accessing the cache - either
305 fsgid and actor security label) that the process acts as - without changing the
312  (1) Finds the security label attached to the root cache directory and uses
329      based on a rule of this form in the policy::
331 	type_transition <daemon's-ID> kernel_t : process <module's-ID>;
351 	https://people.redhat.com/~dhowells/fscache/cachefilesd-0.8.tar.bz2
361 If a non-RPM based system is being used, then copy the above files to their own
362 directory and run::
364 	make -f /usr/share/selinux/devel/Makefile
365 	semodule -i cachefilesd.pp
367 You will need checkpolicy and selinux-policy-devel installed prior to the
379 	/usr/share/doc/cachefilesd-*/move-cache.txt
389 its own task_security structure, and redirects current->cred to point to it
398 Furthermore, should CacheFiles create a file or directory, the security
401 preventing other processes from accessing the cache - including CacheFiles's
405 issued the system call.  We can't, however, just do an in-place change of the
411 objective security (task->real_cred) and the subjective security (task->cred).
430 If FS-Cache is compiled with the following option enabled::
445      between 0 jiffies and HZ-1 jiffies a variety of tasks took to run.  The