- ===============================================
- CacheFiles: CACHE ON ALREADY MOUNTED FILESYSTEM
- ===============================================
+.. SPDX-License-Identifier: GPL-2.0
-Contents:
+===============================================
+CacheFiles: CACHE ON ALREADY MOUNTED FILESYSTEM
+===============================================
+
+.. Contents:
(*) Overview.
(*) Debugging.
-========
-OVERVIEW
+
+Overview
========
CacheFiles is a caching backend that's meant to use as a cache a directory on
space.
-============
-REQUIREMENTS
+
+Requirements
============
The use of CacheFiles and its daemon requires the following features to be
filesystems being used as a cache.
-=============
-CONFIGURATION
+Configuration
=============
The cache is configured by a script in /etc/cachefilesd.conf. These commands
set up cache ready for use. The following script commands are available:
- (*) brun <N>%
- (*) bcull <N>%
- (*) bstop <N>%
- (*) frun <N>%
- (*) fcull <N>%
- (*) fstop <N>%
-
+ brun <N>%, bcull <N>%, bstop <N>%, frun <N>%, fcull <N>%, fstop <N>%
Configure the culling limits. Optional. See the section on culling
The defaults are 7% (run), 5% (cull) and 1% (stop) respectively.
The commands beginning with a 'b' are file space (block) limits, those
beginning with an 'f' are file count limits.
- (*) dir <path>
-
+ dir <path>
Specify the directory containing the root of the cache. Mandatory.
- (*) tag <name>
-
+ tag <name>
Specify a tag to FS-Cache to use in distinguishing multiple caches.
Optional. The default is "CacheFiles".
- (*) debug <mask>
-
+ debug <mask>
Specify a numeric bitmask to control debugging in the kernel module.
Optional. The default is zero (all off). The following values can be
OR'd into the mask to collect various information:
+ == =================================================
1 Turn on trace of function entry (_enter() macros)
2 Turn on trace of function exit (_leave() macros)
4 Turn on trace of internal debug points (_debug())
+ == =================================================
- This mask can also be set through sysfs, eg:
+ This mask can also be set through sysfs, eg::
echo 5 >/sys/modules/cachefiles/parameters/debug
-==================
-STARTING THE CACHE
+Starting the Cache
==================
The cache is started by running the daemon. The daemon opens the cache device,
configures the cache and tells it to begin caching. At that point the cache
binds to fscache and the cache becomes live.
-The daemon is run as follows:
+The daemon is run as follows::
/sbin/cachefilesd [-d]* [-s] [-n] [-f <configfile>]
The flags are:
- (*) -d
-
+ ``-d``
Increase the debugging level. This can be specified multiple times and
is cumulative with itself.
- (*) -s
-
+ ``-s``
Send messages to stderr instead of syslog.
- (*) -n
-
+ ``-n``
Don't daemonise and go into background.
- (*) -f <configfile>
-
+ ``-f <configfile>``
Use an alternative configuration file rather than the default one.
-===============
-THINGS TO AVOID
+Things to Avoid
===============
Do not mount other things within the cache as this will cause problems. The
permissions to prevent random users being able to access them directly.
-=============
-CACHE CULLING
+Cache Culling
=============
The cache may need culling occasionally to make space. This involves
percentage of files available in the underlying filesystem. There are six
"limits":
- (*) brun
- (*) frun
-
+ brun, frun
If the amount of free space and the number of available files in the cache
rises above both these limits, then culling is turned off.
- (*) bcull
- (*) fcull
-
+ bcull, fcull
If the amount of available space or the number of available files in the
cache falls below either of these limits, then culling is started.
- (*) bstop
- (*) fstop
-
+ bstop, fstop
If the amount of available space or the number of available files in the
cache falls below either of these limits, then no further allocation of
disk space or files is permitted until culling has raised things above
these limits again.
-These must be configured thusly:
+These must be configured thusly::
0 <= bstop < bcull < brun < 100
0 <= fstop < fcull < frun < 100
their atimes have changed or if the kernel module says it is still using them.
-===============
-CACHE STRUCTURE
+Cache Structure
===============
The CacheFiles module will create two directories in the directory it was
given:
- (*) cache/
-
- (*) graveyard/
+ * cache/
+ * graveyard/
The active cache objects all reside in the first directory. The CacheFiles
kernel module moves any retired or culled objects that it can't simply unlink
Immediately in the representative directory are a collection of directories
named for hash values of the child object keys with an '@' prepended. Into
this directory, if possible, will be placed the representations of the child
-objects:
+objects::
- INDEX INDEX INDEX DATA FILES
- ========= ========== ================================= ================
+ /INDEX /INDEX /INDEX /DATA FILES
+ /=========/==========/=================================/================
cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400
cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...DB1ry
cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...N22ry
it, then it will be cut into pieces, the first few of which will be used to
make a nest of directories, and the last one of which will be the objects
inside the last directory. The names of the intermediate directories will have
-'+' prepended:
+'+' prepended::
J1223/@23/+xy...z/+kl...m/Epqr
"base-64" encode ones that aren't directly suitable. The two versions of
object filenames indicate the encoding:
+ =============== =============== ===============
OBJECT TYPE PRINTABLE ENCODED
=============== =============== ===============
Index "I..." "J..."
Data "D..." "E..."
Special "S..." "T..."
+ =============== =============== ===============
Intermediate directories are always "@" or "+" as appropriate.
any file of an incorrect type (such as a FIFO file or a device file).
-==========================
-SECURITY MODEL AND SELINUX
+Security Model and SELinux
==========================
CacheFiles is implemented to deal properly with the LSM security features of
(1) Finds the security label attached to the root cache directory and uses
that as the security label with which it will create files. By default,
- this is:
+ this is::
cachefiles_var_t
(2) Finds the security label of the process which issued the bind request
- (presumed to be the cachefilesd daemon), which by default will be:
+ (presumed to be the cachefilesd daemon), which by default will be::
cachefilesd_t
and asks LSM to supply a security ID as which it should act given the
- daemon's label. By default, this will be:
+ daemon's label. By default, this will be::
cachefiles_kernel_t
SELinux transitions the daemon's security ID to the module's security ID
- based on a rule of this form in the policy.
+ based on a rule of this form in the policy::
type_transition <daemon's-ID> kernel_t : process <module's-ID>;
- For instance:
+ For instance::
type_transition cachefilesd_t kernel_t : process cachefiles_kernel_t;
http://people.redhat.com/~dhowells/fscache/cachefilesd-0.8.tar.bz2
-and later versions. In that tarball, see the files:
+and later versions. In that tarball, see the files::
cachefilesd.te
cachefilesd.fc
They are built and installed directly by the RPM.
If a non-RPM based system is being used, then copy the above files to their own
-directory and run:
+directory and run::
make -f /usr/share/selinux/devel/Makefile
semodule -i cachefilesd.pp
cache.
For instructions on how to add an auxiliary policy to enable the cache to be
-located elsewhere when SELinux is in enforcing mode, please see:
+located elsewhere when SELinux is in enforcing mode, please see::
/usr/share/doc/cachefilesd-*/move-cache.txt
in the sources.
-==================
-A NOTE ON SECURITY
+A Note on Security
==================
CacheFiles makes use of the split security in the task_struct. It allocates
files and directories with another security label.
-=======================
-STATISTICAL INFORMATION
+Statistical Information
=======================
-If FS-Cache is compiled with the following option enabled:
+If FS-Cache is compiled with the following option enabled::
CONFIG_CACHEFILES_HISTOGRAM=y
then it will gather certain statistics and display them through a proc file.
- (*) /proc/fs/cachefiles/histogram
+ /proc/fs/cachefiles/histogram
+
+ ::
cat /proc/fs/cachefiles/histogram
JIFS SECS LOOKUPS MKDIRS CREATES
between 0 jiffies and HZ-1 jiffies a variety of tasks took to run. The
columns are as follows:
+ ======= =======================================================
COLUMN TIME MEASUREMENT
======= =======================================================
LOOKUPS Length of time to perform a lookup on the backing fs
MKDIRS Length of time to perform a mkdir on the backing fs
CREATES Length of time to perform a create on the backing fs
+ ======= =======================================================
Each row shows the number of events that took a particular range of times.
Each step is 1 jiffy in size. The JIFS column indicates the particular
jiffy range covered, and the SECS field the equivalent number of seconds.
-=========
-DEBUGGING
+Debugging
=========
If CONFIG_CACHEFILES_DEBUG is enabled, the CacheFiles facility can have runtime
-debugging enabled by adjusting the value in:
+debugging enabled by adjusting the value in::
/sys/module/cachefiles/parameters/debug
This is a bitmask of debugging streams to enable:
+ ======= ======= =============================== =======================
BIT VALUE STREAM POINT
======= ======= =============================== =======================
0 1 General Function entry trace
1 2 Function exit trace
2 4 General
+ ======= ======= =============================== =======================
The appropriate set of values should be OR'd together and the result written to
-the control file. For example:
+the control file. For example::
echo $((1|4|8)) >/sys/module/cachefiles/parameters/debug
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