filesystems/caching/cachefiles.rst

1 .. SPDX-License-Identifier: GPL-2.0
31  (*) On-demand Read.
40 CacheFiles uses a userspace daemon to do some of the cache management - such as
49 CacheFiles creates a misc character device - "/dev/cachefiles" - that is used
58 space if necessary - see the "Cache Culling" section.  This means it can be
71 	- dnotify.
73 	- extended attributes (xattrs).
75 	- openat() and friends.
77 	- bmap() support on files in the filesystem (FIBMAP ioctl).
79 	- The use of bmap() to detect a partial page at the end of the file.
102 	Specify a tag to FS-Cache to use in distinguishing multiple caches.
130 	/sbin/cachefilesd [-d]* [-s] [-n] [-f <configfile>]
134  ``-d``
138  ``-s``
141  ``-n``
144  ``-f <configfile>``
152 kernel module contains its own very cut-down path walking facility that ignores
248 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400
249 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...DB1ry
250 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...N22ry
251 	cache/@4a/I03nfs/@30/Ji000000000000000--fHg8hi8400/@75/Es0g000w...FP1ry
268 "base-64" encode ones that aren't directly suitable.  The two versions of
300 security context that is not appropriate for accessing the cache - either
306 fsgid and actor security label) that the process acts as - without changing the
332 	type_transition <daemon's-ID> kernel_t : process <module's-ID>;
352 	https://people.redhat.com/~dhowells/fscache/cachefilesd-0.8.tar.bz2
360 They are built and installed directly by the RPM.
362 If a non-RPM based system is being used, then copy the above files to their own
365 	make -f /usr/share/selinux/devel/Makefile
366 	semodule -i cachefilesd.pp
368 You will need checkpolicy and selinux-policy-devel installed prior to the
380 	/usr/share/doc/cachefilesd-*/move-cache.txt
382 When the cachefilesd rpm is installed; alternatively, the document can be found
390 its own task_security structure, and redirects current->cred to point to it
402 preventing other processes from accessing the cache - including CacheFiles's
406 issued the system call.  We can't, however, just do an in-place change of the
409 the process looks like in /proc.
412 objective security (task->real_cred) and the subjective security (task->cred).
414 is never overridden.  This is what appears in /proc, and is what is used when a
431 If FS-Cache is compiled with the following option enabled::
435 then it will gather certain statistics and display them through a proc file.
437  /proc/fs/cachefiles/histogram
441 	cat /proc/fs/cachefiles/histogram
446      between 0 jiffies and HZ-1 jiffies a variety of tasks took to run.  The
488 On-demand Read
492 remote networking fs - while in on-demand read mode, CacheFiles can boost the
493 scenario where on-demand read semantics are needed, e.g. container image
498 server and then write it to the cache file; in on-demand read mode, fetching
501 ``CONFIG_CACHEFILES_ONDEMAND`` should be enabled to support on-demand read mode.
505 ----------------------
507 The on-demand read mode uses a simple protocol for communication between kernel
510 	kernel --[request]--> user daemon --[reply]--> kernel
543 	  header and following type-specific payload.
546 Turning on On-demand Mode
547 -------------------------
554 When it is given the "ondemand" argument, i.e. "bind ondemand", on-demand read
559 ----------------
576 	  The volume key is a NUL-terminated string; the cookie key is binary
600 ``/proc/sys/fs/nr_open`` and ``/proc/sys/fs/file-max``.  Typically these needn't
619 -----------------
628 ----------------
630 When a cache miss is encountered in on-demand read mode, CacheFiles will send a