[PATCH 00/37] Permit filesystem local caching [ver #34]

From: David Howells
Date: Thu Feb 28 2008 - 19:44:38 EST

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These patches add local caching for network filesystems such as NFS. To give a
really quick overview of the way the facility works:

+---------+
| |
| NFS |--+
| | |
+---------+ | +----------+
| | |
+---------+ +-->| |
| | | |
| AFS |----->| FS-Cache |
| | | |--+
+---------+ +-->| | |
| | | | +--------------+ +--------------+
+---------+ | +----------+ | | | | |
| | | +-->| CacheFiles |-->| Ext3 |
| ISOFS |--+ | /var/cache | | /dev/sda6 |
| | +--------------+ +--------------+
+---------+

(1) NFS, say, asks FS-Cache to store/retrieve data for it;

(2) FS-Cache asks the cache backend, in this case CacheFiles to honour the
operation;

(3) CacheFiles 'opens' a file in a mounted filesystem, say Ext3, and does read
and write operations of a sort on it;

(4) Ext3 decides how the cache data is laid out on disk - CacheFiles just
attempts to use one sparse file per netfs inode.

(5) If NFS asks for data from the cache, but the file has a hole in it, NFS
falls back to asking the server. The data obtained from the server is
then written over the hole in the file.

To look at it another way:

+---------+
| |
| Server |
| |
+---------+
| NETWORK
~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
| +----------+
V | |
+---------+ | |
| | | |
| NFS |----->| FS-Cache |
| | | |--+
+---------+ | | | +--------------+ +--------------+
| | | | | | | |
V +----------+ +-->| CacheFiles |-->| Ext3 |
+---------+ | /var/cache | | /dev/sda6 |
| | +--------------+ +--------------+
| VFS | ^ ^
| | | |
+---------+ +--------------+ |
| KERNEL SPACE | |
~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~|~~~~
| USER SPACE | |
V | |
+---------+ +--------------+
| | | |
| Process | | cachefilesd |
| | | |
+---------+ +--------------+

FS-Cache attempts to provide a caching facility to a network filesystem such
that it's transparent to the users of that network filesystem.

The patches can roughly be broken down into a number of sets:

(*) 01-keys-inc-payload.diff
(*) 02-keys-search-keyring.diff
(*) 03-keys-callout-blob.diff

Three patches to the keyring code made to help the CIFS people.
Included because patches 05-07 modify the same code.

(*) 04-keys-get-label.diff

A patch to allow the security label of a key to be retrieved.
Included because patches 05-07 modify the same code.

(*) 05-security-current-fsugid.diff
(*) 06-security-separate-task-bits.diff
(*) 07-security-subjective.diff
(*) 08-security-kernel_service-class.diff
(*) 09-security-kernel-service.diff
(*) 10-security-nfsd.diff

Patches to permit the subjective security of a task to be overridden.
All the security details in task_struct are decanted into a new struct
that task_struct then has two pointers two: one that defines the
objective security of that task (how other tasks may affect it) and one
that defines the subjective security (how it may affect other objects).

Note that I have dropped the idea of struct cred for the moment. With
the amount of stuff that was excluded from it, it wasn't actually any
use to me. However, it can be added later.

This is required for CacheFiles and potentially other cache backends:

It has been required that I call vfs_mkdir() and suchlike rather than
bypassing security and calling inode ops directly. Therefore the VFS
and LSM get to deny the cache backend access to the cache data because
under some circumstances the caching code is running in the security
context of whatever process issued the original syscall on the netfs.

Furthermore, the security parameters with which a file is created (UID,
GID, security label) would be derived from that process that issued the
system call, thus potentially preventing other processes from accessing
the cache, including cache management daemons such as cachefilesd.

What is required is to temporarily override the security of the process
that issued the system call. We can't, however, just do an in-place
change of the security data as that affects the process as an object,
not just as a subject. This means it may lose signals or ptrace events
for example, and affects what the process looks like in /proc.

So what I've done is to make a logical split in the security between
the objective security (task->sec) and the subjective security
(task->act_as). The objective security holds the intrinsic security
properties of a process and is never overridden. This is what appears
in /proc, and is what is used when a process is the target of an
operation by some other process (SIGKILL for example).

The subjective security holds the active security properties of a
process, and may be overridden. This is not seen externally, and is
used whan a process acts upon another object, for example SIGKILLing
another process or opening a file.

The new hooks allow SELinux (or Smack or whatever) to reject a request
for a kernel service (such as cachefiles) to run in a context of a
specific security label or to create files and directories with another
security label.

These hooks may also be useful for NFSd.

(*) 11-release-page.diff
(*) 12-fscache-page-flags.diff
(*) 13-add_wait_queue_tail.diff
(*) 14-fscache.diff

Patches to provide a local caching facility for network filesystems.

FS-Cache is a layer that takes requests from any one of a number of
netfs's and passes them to an appropriate cache, if there is one.
FS-Cache makes operations requested by the netfs transparently
asynchronous where possible.

FS-Cache also protects the netfs against (a) there being no cache, (b)
the cache suffering a fatal I/O error and (c) the cache being removed;
and protects the cache against (d) the netfs uncaching pages that the
cache is using and (e) conflicting operations from the netfs, some of
which may be queued for asynchronous processing.

A number of documents in text file format that describe the FS-Cache
interface are added by the latter patch

Documentation/filesystems/caching/fscache.txt gives an overview of the
facility and describes the statistical data it makes available.

Documentation/filesystems/caching/netfs-api.txt describes the API by
which a network filesystem would make use of the FS-Cache facility.

Documentation/filesystems/caching/backend-api.txt describes the API that
a cache backend must implement to provide caching services through
FS-Cache.

The second of the above patches adds two extra page flags that FS-Cache
then uses to keep track of two bits of per-cached-page information:

(1) This page is known by the cache, and that the cache must be
informed if the page is going to go away. It's an indication to
the netfs that the cache has an interest in this page, where an
interest may be a pointer to it, resources allocated or reserved
for it, or I/O in progress upon it.

(2) This page is being written to disk by the cache, and that it
cannot be released until completion. Ideally it shouldn't be
changed until completion either so as to maintain the known state
of the cache. This cannot be unified with PG_writeback as the
page may be being written to both the server and the cache at the
same time or at different times.

To avoid using extra page bits, I could, for example, set up a radix tree
per data storage object to keep track of both these bits, however this
would mean that the netfs would have to do a call, spinlock, conditional
jumps, etc to find out either state.

On the other hand, if we can spare two page flags, those are sufficient.

Note that the cache doesn't necessarily need to be able to find the netfs
pages, but may have to allocate/pin resources for backing them.

Further note that PG_private may not be used as I want to be able to use
caching with ISOFS eventually, and PG_private is owned by the block
buffer code.

These bits can be otherwise used by any filesystem that doesn't want to
use FS-Cache.

(*) 15-cachefiles-ia64.diff
(*) 16-cachefiles-ext3-f_mapping.diff
(*) 17-cachefiles-write.diff
(*) 18-cachefiles-monitor.diff
(*) 19-cachefiles-export.diff
(*) 20-cachefiles.diff

Patches to provide a local cache in a directory of an already mounted
filesystem.

The latter patch adds a document in text file format that describes the
CacheFiles cache backend and gives instructions on how it is set up and
used. This will be Documentation/filesystems/caching/cachefiles.txt when
the patch is applied.

(*) 21-nfs-comment.diff
(*) 22-nfs-fscache-option.diff
(*) 23-nfs-fscache-kconfig.diff
(*) 24-nfs-fscache-top-index.diff
(*) 25-nfs-fscache-server-obj.diff
(*) 26-nfs-fscache-super-obj.diff
(*) 27-nfs-fscache-inode-obj.diff
(*) 28-nfs-fscache-use-inode.diff
(*) 29-nfs-fscache-invalidate-pages.diff
(*) 30-nfs-fscache-iostats.diff
(*) 31-nfs-fscache-page-management.diff
(*) 32-nfs-fscache-read-context.diff
(*) 33-nfs-fscache-read-fallback.diff
(*) 34-nfs-fscache-read-from-cache.diff
(*) 35-nfs-fscache-store-to-cache.diff
(*) 36-nfs-fscache-mount.diff
(*) 37-nfs-fscache-display.diff

Patches to provide NFS with local caching.

A couple of questions on the NFS iostat changes: (1) Should I update the
iostat version number; (2) is it permitted to have conditional iostats?

I've fixed a number of bugs, including the lack of locking around per-inode
cookie handling in NFS, and updated the documentation in a couple of patches.

I've been testing these patches by throwing batches of eight parallel "tar cf"
commands across three different 350MB NFS-based kernel trees (3 tars on first
tree, 3 on second, 2 on third), sometimes with one or more of the trees
preloaded into the cache. The complete working data set does not fit into the
RAM of my test machine, so even three tars that can be entirely satisfied from
the cache may have to reread everything from disk.

--
A tarball of the patches is available at:

http://people.redhat.com/~dhowells/fscache/patches/nfs+fscache-34.tar.bz2

To use this version of CacheFiles, the cachefilesd-0.9 is also required. It
is available as an SRPM:

http://people.redhat.com/~dhowells/fscache/cachefilesd-0.9-1.fc7.src.rpm

Or as individual bits:

http://people.redhat.com/~dhowells/fscache/cachefilesd-0.9.tar.bz2
http://people.redhat.com/~dhowells/fscache/cachefilesd.fc
http://people.redhat.com/~dhowells/fscache/cachefilesd.if
http://people.redhat.com/~dhowells/fscache/cachefilesd.te
http://people.redhat.com/~dhowells/fscache/cachefilesd.spec

The .fc, .if and .te files are for manipulating SELinux.

David
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Next message: David Howells: "[PATCH 01/37] KEYS: Increase the payload size when instantiating akey [ver #34]"
Previous message: J.C. Pizarro: "Re: [RFC, PATCH 1/2] sched: change the fairness model of the CFS group scheduler"
Next in thread: David Howells: "[PATCH 01/37] KEYS: Increase the payload size when instantiating akey [ver #34]"
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