6 files changed, 624 insertions, 327 deletions

diff --git a/Documentation/filesystems/dentry-locking.txt b/Documentation/filesystems/dentry-locking.txt
new file mode 100644
index 000000000000..4c0c575a4012
--- /dev/null
+++ b/Documentation/filesystems/dentry-locking.txt
@@ -0,0 +1,173 @@
+RCU-based dcache locking model
+==============================
+
+On many workloads, the most common operation on dcache is to look up a
+dentry, given a parent dentry and the name of the child. Typically,
+for every open(), stat() etc., the dentry corresponding to the
+pathname will be looked up by walking the tree starting with the first
+component of the pathname and using that dentry along with the next
+component to look up the next level and so on. Since it is a frequent
+operation for workloads like multiuser environments and web servers,
+it is important to optimize this path.
+
+Prior to 2.5.10, dcache_lock was acquired in d_lookup and thus in
+every component during path look-up. Since 2.5.10 onwards, fast-walk
+algorithm changed this by holding the dcache_lock at the beginning and
+walking as many cached path component dentries as possible. This
+significantly decreases the number of acquisition of
+dcache_lock. However it also increases the lock hold time
+significantly and affects performance in large SMP machines. Since
+2.5.62 kernel, dcache has been using a new locking model that uses RCU
+to make dcache look-up lock-free.
+
+The current dcache locking model is not very different from the
+existing dcache locking model. Prior to 2.5.62 kernel, dcache_lock
+protected the hash chain, d_child, d_alias, d_lru lists as well as
+d_inode and several other things like mount look-up. RCU-based changes
+affect only the way the hash chain is protected. For everything else
+the dcache_lock must be taken for both traversing as well as
+updating. The hash chain updates too take the dcache_lock.  The
+significant change is the way d_lookup traverses the hash chain, it
+doesn't acquire the dcache_lock for this and rely on RCU to ensure
+that the dentry has not been *freed*.
+
+
+Dcache locking details
+======================
+
+For many multi-user workloads, open() and stat() on files are very
+frequently occurring operations. Both involve walking of path names to
+find the dentry corresponding to the concerned file. In 2.4 kernel,
+dcache_lock was held during look-up of each path component. Contention
+and cache-line bouncing of this global lock caused significant
+scalability problems. With the introduction of RCU in Linux kernel,
+this was worked around by making the look-up of path components during
+path walking lock-free.
+
+
+Safe lock-free look-up of dcache hash table
+===========================================
+
+Dcache is a complex data structure with the hash table entries also
+linked together in other lists. In 2.4 kernel, dcache_lock protected
+all the lists. We applied RCU only on hash chain walking. The rest of
+the lists are still protected by dcache_lock.  Some of the important
+changes are :
+
+1. The deletion from hash chain is done using hlist_del_rcu() macro
+   which doesn't initialize next pointer of the deleted dentry and
+   this allows us to walk safely lock-free while a deletion is
+   happening.
+
+2. Insertion of a dentry into the hash table is done using
+   hlist_add_head_rcu() which take care of ordering the writes - the
+   writes to the dentry must be visible before the dentry is
+   inserted. This works in conjunction with hlist_for_each_rcu() while
+   walking the hash chain. The only requirement is that all
+   initialization to the dentry must be done before
+   hlist_add_head_rcu() since we don't have dcache_lock protection
+   while traversing the hash chain. This isn't different from the
+   existing code.
+
+3. The dentry looked up without holding dcache_lock by cannot be
+   returned for walking if it is unhashed. It then may have a NULL
+   d_inode or other bogosity since RCU doesn't protect the other
+   fields in the dentry. We therefore use a flag DCACHE_UNHASHED to
+   indicate unhashed dentries and use this in conjunction with a
+   per-dentry lock (d_lock). Once looked up without the dcache_lock,
+   we acquire the per-dentry lock (d_lock) and check if the dentry is
+   unhashed. If so, the look-up is failed. If not, the reference count
+   of the dentry is increased and the dentry is returned.
+
+4. Once a dentry is looked up, it must be ensured during the path walk
+   for that component it doesn't go away. In pre-2.5.10 code, this was
+   done holding a reference to the dentry. dcache_rcu does the same.
+   In some sense, dcache_rcu path walking looks like the pre-2.5.10
+   version.
+
+5. All dentry hash chain updates must take the dcache_lock as well as
+   the per-dentry lock in that order. dput() does this to ensure that
+   a dentry that has just been looked up in another CPU doesn't get
+   deleted before dget() can be done on it.
+
+6. There are several ways to do reference counting of RCU protected
+   objects. One such example is in ipv4 route cache where deferred
+   freeing (using call_rcu()) is done as soon as the reference count
+   goes to zero. This cannot be done in the case of dentries because
+   tearing down of dentries require blocking (dentry_iput()) which
+   isn't supported from RCU callbacks. Instead, tearing down of
+   dentries happen synchronously in dput(), but actual freeing happens
+   later when RCU grace period is over. This allows safe lock-free
+   walking of the hash chains, but a matched dentry may have been
+   partially torn down. The checking of DCACHE_UNHASHED flag with
+   d_lock held detects such dentries and prevents them from being
+   returned from look-up.
+
+
+Maintaining POSIX rename semantics
+==================================
+
+Since look-up of dentries is lock-free, it can race against a
+concurrent rename operation. For example, during rename of file A to
+B, look-up of either A or B must succeed.  So, if look-up of B happens
+after A has been removed from the hash chain but not added to the new
+hash chain, it may fail.  Also, a comparison while the name is being
+written concurrently by a rename may result in false positive matches
+violating rename semantics.  Issues related to race with rename are
+handled as described below :
+
+1. Look-up can be done in two ways - d_lookup() which is safe from
+   simultaneous renames and __d_lookup() which is not.  If
+   __d_lookup() fails, it must be followed up by a d_lookup() to
+   correctly determine whether a dentry is in the hash table or
+   not. d_lookup() protects look-ups using a sequence lock
+   (rename_lock).
+
+2. The name associated with a dentry (d_name) may be changed if a
+   rename is allowed to happen simultaneously. To avoid memcmp() in
+   __d_lookup() go out of bounds due to a rename and false positive
+   comparison, the name comparison is done while holding the
+   per-dentry lock. This prevents concurrent renames during this
+   operation.
+
+3. Hash table walking during look-up may move to a different bucket as
+   the current dentry is moved to a different bucket due to rename.
+   But we use hlists in dcache hash table and they are
+   null-terminated.  So, even if a dentry moves to a different bucket,
+   hash chain walk will terminate. [with a list_head list, it may not
+   since termination is when the list_head in the original bucket is
+   reached].  Since we redo the d_parent check and compare name while
+   holding d_lock, lock-free look-up will not race against d_move().
+
+4. There can be a theoretical race when a dentry keeps coming back to
+   original bucket due to double moves. Due to this look-up may
+   consider that it has never moved and can end up in a infinite loop.
+   But this is not any worse that theoretical livelocks we already
+   have in the kernel.
+
+
+Important guidelines for filesystem developers related to dcache_rcu
+====================================================================
+
+1. Existing dcache interfaces (pre-2.5.62) exported to filesystem
+   don't change. Only dcache internal implementation changes. However
+   filesystems *must not* delete from the dentry hash chains directly
+   using the list macros like allowed earlier. They must use dcache
+   APIs like d_drop() or __d_drop() depending on the situation.
+
+2. d_flags is now protected by a per-dentry lock (d_lock). All access
+   to d_flags must be protected by it.
+
+3. For a hashed dentry, checking of d_count needs to be protected by
+   d_lock.
+
+
+Papers and other documentation on dcache locking
+================================================
+
+1. Scaling dcache with RCU (http://linuxjournal.com/article.php?sid=7124).
+
+2. http://lse.sourceforge.net/locking/dcache/dcache.html
+
+
+
diff --git a/Documentation/filesystems/devfs/README b/Documentation/filesystems/devfs/README
index 54366ecc241f..aabfba24bc2e 100644
--- a/Documentation/filesystems/devfs/README
+++ b/Documentation/filesystems/devfs/README
@@ -1812,11 +1812,6 @@ it may overflow the messages buffer, but try to get as much of it as
 you can
 
 
-if you get an Oops, run ksymoops to decode it so that the
-names of the offending functions are provided. A non-decoded Oops is
-pretty useless
-
-
 send a copy of your devfsd configuration file(s)
 
 send the bug report to me first.
diff --git a/Documentation/filesystems/ext2.txt b/Documentation/filesystems/ext2.txt
index d16334ec48ba..a8edb376b041 100644
--- a/Documentation/filesystems/ext2.txt
+++ b/Documentation/filesystems/ext2.txt
@@ -17,8 +17,6 @@ set using tune2fs(8). Kernel-determined defaults are indicated by (*).
 bsddf                   (*)     Makes `df' act like BSD.
 minixdf                         Makes `df' act like Minix.
 
-check                           Check block and inode bitmaps at mount time
-                                (requires CONFIG_EXT2_CHECK).
 check=none, nocheck     (*)     Don't do extra checking of bitmaps on mount
                                 (check=normal and check=strict options removed)
 
diff --git a/Documentation/filesystems/ramfs-rootfs-initramfs.txt b/Documentation/filesystems/ramfs-rootfs-initramfs.txt
new file mode 100644
index 000000000000..b3404a032596
--- /dev/null
+++ b/Documentation/filesystems/ramfs-rootfs-initramfs.txt
@@ -0,0 +1,195 @@
+ramfs, rootfs and initramfs
+October 17, 2005
+Rob Landley <rob@landley.net>
+=============================
+
+What is ramfs?
+--------------
+
+Ramfs is a very simple filesystem that exports Linux's disk caching
+mechanisms (the page cache and dentry cache) as a dynamically resizable
+ram-based filesystem.
+
+Normally all files are cached in memory by Linux.  Pages of data read from
+backing store (usually the block device the filesystem is mounted on) are kept
+around in case it's needed again, but marked as clean (freeable) in case the
+Virtual Memory system needs the memory for something else.  Similarly, data
+written to files is marked clean as soon as it has been written to backing
+store, but kept around for caching purposes until the VM reallocates the
+memory.  A similar mechanism (the dentry cache) greatly speeds up access to
+directories.
+
+With ramfs, there is no backing store.  Files written into ramfs allocate
+dentries and page cache as usual, but there's nowhere to write them to.
+This means the pages are never marked clean, so they can't be freed by the
+VM when it's looking to recycle memory.
+
+The amount of code required to implement ramfs is tiny, because all the
+work is done by the existing Linux caching infrastructure.  Basically,
+you're mounting the disk cache as a filesystem.  Because of this, ramfs is not
+an optional component removable via menuconfig, since there would be negligible
+space savings.
+
+ramfs and ramdisk:
+------------------
+
+The older "ram disk" mechanism created a synthetic block device out of
+an area of ram and used it as backing store for a filesystem.  This block
+device was of fixed size, so the filesystem mounted on it was of fixed
+size.  Using a ram disk also required unnecessarily copying memory from the
+fake block device into the page cache (and copying changes back out), as well
+as creating and destroying dentries.  Plus it needed a filesystem driver
+(such as ext2) to format and interpret this data.
+
+Compared to ramfs, this wastes memory (and memory bus bandwidth), creates
+unnecessary work for the CPU, and pollutes the CPU caches.  (There are tricks
+to avoid this copying by playing with the page tables, but they're unpleasantly
+complicated and turn out to be about as expensive as the copying anyway.)
+More to the point, all the work ramfs is doing has to happen _anyway_,
+since all file access goes through the page and dentry caches.  The ram
+disk is simply unnecessary, ramfs is internally much simpler.
+
+Another reason ramdisks are semi-obsolete is that the introduction of
+loopback devices offered a more flexible and convenient way to create
+synthetic block devices, now from files instead of from chunks of memory.
+See losetup (8) for details.
+
+ramfs and tmpfs:
+----------------
+
+One downside of ramfs is you can keep writing data into it until you fill
+up all memory, and the VM can't free it because the VM thinks that files
+should get written to backing store (rather than swap space), but ramfs hasn't
+got any backing store.  Because of this, only root (or a trusted user) should
+be allowed write access to a ramfs mount.
+
+A ramfs derivative called tmpfs was created to add size limits, and the ability
+to write the data to swap space.  Normal users can be allowed write access to
+tmpfs mounts.  See Documentation/filesystems/tmpfs.txt for more information.
+
+What is rootfs?
+---------------
+
+Rootfs is a special instance of ramfs, which is always present in 2.6 systems.
+(It's used internally as the starting and stopping point for searches of the
+kernel's doubly-linked list of mount points.)
+
+Most systems just mount another filesystem over it and ignore it.  The
+amount of space an empty instance of ramfs takes up is tiny.
+
+What is initramfs?
+------------------
+
+All 2.6 Linux kernels contain a gzipped "cpio" format archive, which is
+extracted into rootfs when the kernel boots up.  After extracting, the kernel
+checks to see if rootfs contains a file "init", and if so it executes it as PID
+1.  If found, this init process is responsible for bringing the system the
+rest of the way up, including locating and mounting the real root device (if
+any).  If rootfs does not contain an init program after the embedded cpio
+archive is extracted into it, the kernel will fall through to the older code
+to locate and mount a root partition, then exec some variant of /sbin/init
+out of that.
+
+All this differs from the old initrd in several ways:
+
+  - The old initrd was a separate file, while the initramfs archive is linked
+    into the linux kernel image.  (The directory linux-*/usr is devoted to
+    generating this archive during the build.)
+
+  - The old initrd file was a gzipped filesystem image (in some file format,
+    such as ext2, that had to be built into the kernel), while the new
+    initramfs archive is a gzipped cpio archive (like tar only simpler,
+    see cpio(1) and Documentation/early-userspace/buffer-format.txt).
+
+  - The program run by the old initrd (which was called /initrd, not /init) did
+    some setup and then returned to the kernel, while the init program from
+    initramfs is not expected to return to the kernel.  (If /init needs to hand
+    off control it can overmount / with a new root device and exec another init
+    program.  See the switch_root utility, below.)
+
+  - When switching another root device, initrd would pivot_root and then
+    umount the ramdisk.  But initramfs is rootfs: you can neither pivot_root
+    rootfs, nor unmount it.  Instead delete everything out of rootfs to
+    free up the space (find -xdev / -exec rm '{}' ';'), overmount rootfs
+    with the new root (cd /newmount; mount --move . /; chroot .), attach
+    stdin/stdout/stderr to the new /dev/console, and exec the new init.
+
+    Since this is a remarkably persnickity process (and involves deleting
+    commands before you can run them), the klibc package introduced a helper
+    program (utils/run_init.c) to do all this for you.  Most other packages
+    (such as busybox) have named this command "switch_root".
+
+Populating initramfs:
+---------------------
+
+The 2.6 kernel build process always creates a gzipped cpio format initramfs
+archive and links it into the resulting kernel binary.  By default, this
+archive is empty (consuming 134 bytes on x86).  The config option
+CONFIG_INITRAMFS_SOURCE (for some reason buried under devices->block devices
+in menuconfig, and living in usr/Kconfig) can be used to specify a source for
+the initramfs archive, which will automatically be incorporated into the
+resulting binary.  This option can point to an existing gzipped cpio archive, a
+directory containing files to be archived, or a text file specification such
+as the following example:
+
+  dir /dev 755 0 0
+  nod /dev/console 644 0 0 c 5 1
+  nod /dev/loop0 644 0 0 b 7 0
+  dir /bin 755 1000 1000
+  slink /bin/sh busybox 777 0 0
+  file /bin/busybox initramfs/busybox 755 0 0
+  dir /proc 755 0 0
+  dir /sys 755 0 0
+  dir /mnt 755 0 0
+  file /init initramfs/init.sh 755 0 0
+
+One advantage of the text file is that root access is not required to
+set permissions or create device nodes in the new archive.  (Note that those
+two example "file" entries expect to find files named "init.sh" and "busybox" in
+a directory called "initramfs", under the linux-2.6.* directory.  See
+Documentation/early-userspace/README for more details.)
+
+If you don't already understand what shared libraries, devices, and paths
+you need to get a minimal root filesystem up and running, here are some
+references:
+http://www.tldp.org/HOWTO/Bootdisk-HOWTO/
+http://www.tldp.org/HOWTO/From-PowerUp-To-Bash-Prompt-HOWTO.html
+http://www.linuxfromscratch.org/lfs/view/stable/
+
+The "klibc" package (http://www.kernel.org/pub/linux/libs/klibc) is
+designed to be a tiny C library to statically link early userspace
+code against, along with some related utilities.  It is BSD licensed.
+
+I use uClibc (http://www.uclibc.org) and busybox (http://www.busybox.net)
+myself.  These are LGPL and GPL, respectively.
+
+In theory you could use glibc, but that's not well suited for small embedded
+uses like this.  (A "hello world" program statically linked against glibc is
+over 400k.  With uClibc it's 7k.  Also note that glibc dlopens libnss to do
+name lookups, even when otherwise statically linked.)
+
+Future directions:
+------------------
+
+Today (2.6.14), initramfs is always compiled in, but not always used.  The
+kernel falls back to legacy boot code that is reached only if initramfs does
+not contain an /init program.  The fallback is legacy code, there to ensure a
+smooth transition and allowing early boot functionality to gradually move to
+"early userspace" (I.E. initramfs).
+
+The move to early userspace is necessary because finding and mounting the real
+root device is complex.  Root partitions can span multiple devices (raid or
+separate journal).  They can be out on the network (requiring dhcp, setting a
+specific mac address, logging into a server, etc).  They can live on removable
+media, with dynamically allocated major/minor numbers and persistent naming
+issues requiring a full udev implementation to sort out.  They can be
+compressed, encrypted, copy-on-write, loopback mounted, strangely partitioned,
+and so on.
+
+This kind of complexity (which inevitably includes policy) is rightly handled
+in userspace.  Both klibc and busybox/uClibc are working on simple initramfs
+packages to drop into a kernel build, and when standard solutions are ready
+and widely deployed, the kernel's legacy early boot code will become obsolete
+and a candidate for the feature removal schedule.
+
+But that's a while off yet.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index f042c12e0ed2..ee4c0a8b8db7 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -3,7 +3,7 @@
 
         Original author: Richard Gooch <rgooch@atnf.csiro.au>
 
-                  Last updated on August 25, 2005
+                  Last updated on October 28, 2005
 
   Copyright (C) 1999 Richard Gooch
   Copyright (C) 2005 Pekka Enberg
@@ -11,62 +11,61 @@
   This file is released under the GPLv2.
 
 
-What is it?
-===========
+Introduction
+============
 
-The Virtual File System (otherwise known as the Virtual Filesystem
-Switch) is the software layer in the kernel that provides the
-filesystem interface to userspace programs. It also provides an
-abstraction within the kernel which allows different filesystem
-implementations to coexist.
+The Virtual File System (also known as the Virtual Filesystem Switch)
+is the software layer in the kernel that provides the filesystem
+interface to userspace programs. It also provides an abstraction
+within the kernel which allows different filesystem implementations to
+coexist.
 
+VFS system calls open(2), stat(2), read(2), write(2), chmod(2) and so
+on are called from a process context. Filesystem locking is described
+in the document Documentation/filesystems/Locking.
 
-A Quick Look At How It Works
-============================
 
-In this section I'll briefly describe how things work, before
-launching into the details. I'll start with describing what happens
-when user programs open and manipulate files, and then look from the
-other view which is how a filesystem is supported and subsequently
-mounted.
-
-
-Opening a File
---------------
-
-The VFS implements the open(2), stat(2), chmod(2) and similar system
-calls. The pathname argument is used by the VFS to search through the
-directory entry cache (dentry cache or "dcache"). This provides a very
-fast look-up mechanism to translate a pathname (filename) into a
-specific dentry.
-
-An individual dentry usually has a pointer to an inode. Inodes are the
-things that live on disc drives, and can be regular files (you know:
-those things that you write data into), directories, FIFOs and other
-beasts. Dentries live in RAM and are never saved to disc: they exist
-only for performance. Inodes live on disc and are copied into memory
-when required. Later any changes are written back to disc. The inode
-that lives in RAM is a VFS inode, and it is this which the dentry
-points to. A single inode can be pointed to by multiple dentries
-(think about hardlinks).
-
-The dcache is meant to be a view into your entire filespace. Unlike
-Linus, most of us losers can't fit enough dentries into RAM to cover
-all of our filespace, so the dcache has bits missing. In order to
-resolve your pathname into a dentry, the VFS may have to resort to
-creating dentries along the way, and then loading the inode. This is
-done by looking up the inode.
-
-To look up an inode (usually read from disc) requires that the VFS
-calls the lookup() method of the parent directory inode. This method
-is installed by the specific filesystem implementation that the inode
-lives in. There will be more on this later.
+Directory Entry Cache (dcache)
+------------------------------
 
-Once the VFS has the required dentry (and hence the inode), we can do
-all those boring things like open(2) the file, or stat(2) it to peek
-at the inode data. The stat(2) operation is fairly simple: once the
-VFS has the dentry, it peeks at the inode data and passes some of it
-back to userspace.
+The VFS implements the open(2), stat(2), chmod(2), and similar system
+calls. The pathname argument that is passed to them is used by the VFS
+to search through the directory entry cache (also known as the dentry
+cache or dcache). This provides a very fast look-up mechanism to
+translate a pathname (filename) into a specific dentry. Dentries live
+in RAM and are never saved to disc: they exist only for performance.
+
+The dentry cache is meant to be a view into your entire filespace. As
+most computers cannot fit all dentries in the RAM at the same time,
+some bits of the cache are missing. In order to resolve your pathname
+into a dentry, the VFS may have to resort to creating dentries along
+the way, and then loading the inode. This is done by looking up the
+inode.
+
+
+The Inode Object
+----------------
+
+An individual dentry usually has a pointer to an inode. Inodes are
+filesystem objects such as regular files, directories, FIFOs and other
+beasts.  They live either on the disc (for block device filesystems)
+or in the memory (for pseudo filesystems). Inodes that live on the
+disc are copied into the memory when required and changes to the inode
+are written back to disc. A single inode can be pointed to by multiple
+dentries (hard links, for example, do this).
+
+To look up an inode requires that the VFS calls the lookup() method of
+the parent directory inode. This method is installed by the specific
+filesystem implementation that the inode lives in. Once the VFS has
+the required dentry (and hence the inode), we can do all those boring
+things like open(2) the file, or stat(2) it to peek at the inode
+data. The stat(2) operation is fairly simple: once the VFS has the
+dentry, it peeks at the inode data and passes some of it back to
+userspace.
+
+
+The File Object
+---------------
 
 Opening a file requires another operation: allocation of a file
 structure (this is the kernel-side implementation of file
@@ -74,51 +73,39 @@ descriptors). The freshly allocated file structure is initialized with
 a pointer to the dentry and a set of file operation member functions.
 These are taken from the inode data. The open() file method is then
 called so the specific filesystem implementation can do it's work. You
-can see that this is another switch performed by the VFS.
-
-The file structure is placed into the file descriptor table for the
-process.
+can see that this is another switch performed by the VFS. The file
+structure is placed into the file descriptor table for the process.
 
 Reading, writing and closing files (and other assorted VFS operations)
 is done by using the userspace file descriptor to grab the appropriate
-file structure, and then calling the required file structure method
-function to do whatever is required.
-
-For as long as the file is open, it keeps the dentry "open" (in use),
-which in turn means that the VFS inode is still in use.
-
-All VFS system calls (i.e. open(2), stat(2), read(2), write(2),
-chmod(2) and so on) are called from a process context. You should
-assume that these calls are made without any kernel locks being
-held. This means that the processes may be executing the same piece of
-filesystem or driver code at the same time, on different
-processors. You should ensure that access to shared resources is
-protected by appropriate locks.
+file structure, and then calling the required file structure method to
+do whatever is required. For as long as the file is open, it keeps the
+dentry in use, which in turn means that the VFS inode is still in use.
 
 
 Registering and Mounting a Filesystem
--------------------------------------
+=====================================
 
-If you want to support a new kind of filesystem in the kernel, all you
-need to do is call register_filesystem(). You pass a structure
-describing the filesystem implementation (struct file_system_type)
-which is then added to an internal table of supported filesystems. You
-can do:
+To register and unregister a filesystem, use the following API
+functions:
 
-% cat /proc/filesystems
+   #include <linux/fs.h>
 
-to see what filesystems are currently available on your system.
+   extern int register_filesystem(struct file_system_type *);
+   extern int unregister_filesystem(struct file_system_type *);
 
-When a request is made to mount a block device onto a directory in
-your filespace the VFS will call the appropriate method for the
-specific filesystem. The dentry for the mount point will then be
-updated to point to the root inode for the new filesystem.
+The passed struct file_system_type describes your filesystem. When a
+request is made to mount a device onto a directory in your filespace,
+the VFS will call the appropriate get_sb() method for the specific
+filesystem. The dentry for the mount point will then be updated to
+point to the root inode for the new filesystem.
 
-It's now time to look at things in more detail.
+You can see all filesystems that are registered to the kernel in the
+file /proc/filesystems.
 
 
 struct file_system_type
-=======================
+-----------------------
 
 This describes the filesystem. As of kernel 2.6.13, the following
 members are defined:
@@ -197,8 +184,14 @@ A fill_super() method implementation has the following arguments:
   int silent: whether or not to be silent on error
 
 
+The Superblock Object
+=====================
+
+A superblock object represents a mounted filesystem.
+
+
 struct super_operations
-=======================
+-----------------------
 
 This describes how the VFS can manipulate the superblock of your
 filesystem. As of kernel 2.6.13, the following members are defined:
@@ -286,9 +279,9 @@ or bottom half).
         a superblock. The second parameter indicates whether the method
         should wait until the write out has been completed. Optional.
 
-  write_super_lockfs: called when VFS is locking a filesystem and forcing
-        it into a consistent state.  This function is currently used by the
-        Logical Volume Manager (LVM).
+  write_super_lockfs: called when VFS is locking a filesystem and
+        forcing it into a consistent state.  This method is currently
+        used by the Logical Volume Manager (LVM).
 
   unlockfs: called when VFS is unlocking a filesystem and making it writable
         again.
@@ -317,8 +310,14 @@ field. This is a pointer to a "struct inode_operations" which
 describes the methods that can be performed on individual inodes.
 
 
+The Inode Object
+================
+
+An inode object represents an object within the filesystem.
+
+
 struct inode_operations
-=======================
+-----------------------
 
 This describes how the VFS can manipulate an inode in your
 filesystem. As of kernel 2.6.13, the following members are defined:
@@ -394,51 +393,62 @@ otherwise noted.
         will probably need to call d_instantiate() just as you would
         in the create() method
 
+  rename: called by the rename(2) system call to rename the object to
+        have the parent and name given by the second inode and dentry.
+
   readlink: called by the readlink(2) system call. Only required if
         you want to support reading symbolic links
 
   follow_link: called by the VFS to follow a symbolic link to the
         inode it points to.  Only required if you want to support
-        symbolic links.  This function returns a void pointer cookie
+        symbolic links.  This method returns a void pointer cookie
         that is passed to put_link().
 
   put_link: called by the VFS to release resources allocated by
-        follow_link().  The cookie returned by follow_link() is passed to
-        to this function as the last parameter.  It is used by filesystems
-        such as NFS where page cache is not stable (i.e. page that was
-        installed when the symbolic link walk started might not be in the
-        page cache at the end of the walk).
-
-  truncate: called by the VFS to change the size of a file.  The i_size
-        field of the inode is set to the desired size by the VFS before
-        this function is called.  This function is called by the truncate(2)
-        system call and related functionality.
+        follow_link().  The cookie returned by follow_link() is passed
+        to to this method as the last parameter.  It is used by
+        filesystems such as NFS where page cache is not stable
+        (i.e. page that was installed when the symbolic link walk
+        started might not be in the page cache at the end of the
+        walk).
+
+  truncate: called by the VFS to change the size of a file.  The
+        i_size field of the inode is set to the desired size by the
+        VFS before this method is called.  This method is called by
+        the truncate(2) system call and related functionality.
 
   permission: called by the VFS to check for access rights on a POSIX-like
         filesystem.
 
-  setattr: called by the VFS to set attributes for a file.  This function is
-        called by chmod(2) and related system calls.
+  setattr: called by the VFS to set attributes for a file. This method
+        is called by chmod(2) and related system calls.
 
-  getattr: called by the VFS to get attributes of a file.  This function is
-        called by stat(2) and related system calls.
+  getattr: called by the VFS to get attributes of a file. This method
+        is called by stat(2) and related system calls.
 
   setxattr: called by the VFS to set an extended attribute for a file.
-        Extended attribute is a name:value pair associated with an inode. This
-        function is called by setxattr(2) system call.
+        Extended attribute is a name:value pair associated with an
+        inode. This method is called by setxattr(2) system call.
+
+  getxattr: called by the VFS to retrieve the value of an extended
+        attribute name. This method is called by getxattr(2) function
+        call.
 
-  getxattr: called by the VFS to retrieve the value of an extended attribute
-        name.  This function is called by getxattr(2) function call.
+  listxattr: called by the VFS to list all extended attributes for a
+        given file. This method is called by listxattr(2) system call.
 
-  listxattr: called by the VFS to list all extended attributes for a given
-        file.  This function is called by listxattr(2) system call.
+  removexattr: called by the VFS to remove an extended attribute from
+        a file. This method is called by removexattr(2) system call.
 
-  removexattr: called by the VFS to remove an extended attribute from a file.
-        This function is called by removexattr(2) system call.
+
+The Address Space Object
+========================
+
+The address space object is used to identify pages in the page cache.
 
 
 struct address_space_operations
-===============================
+-------------------------------
 
 This describes how the VFS can manipulate mapping of a file to page cache in
 your filesystem. As of kernel 2.6.13, the following members are defined:
@@ -502,8 +512,14 @@ struct address_space_operations {
         it.  An example implementation can be found in fs/ext2/xip.c.
 
 
+The File Object
+===============
+
+A file object represents a file opened by a process.
+
+
 struct file_operations
-======================
+----------------------
 
 This describes how the VFS can manipulate an open file. As of kernel
 2.6.13, the following members are defined:
@@ -661,7 +677,7 @@ of child dentries. Child dentries are basically like files in a
 directory.
 
 
-Directory Entry Cache APIs
+Directory Entry Cache API
 --------------------------
 
 There are a number of functions defined which permit a filesystem to
@@ -705,178 +721,24 @@ manipulate dentries:
         and the dentry is returned. The caller must use d_put()
         to free the dentry when it finishes using it.
 
+For further information on dentry locking, please refer to the document
+Documentation/filesystems/dentry-locking.txt.
 
-RCU-based dcache locking model
-------------------------------
 
-On many workloads, the most common operation on dcache is
-to look up a dentry, given a parent dentry and the name
-of the child. Typically, for every open(), stat() etc.,
-the dentry corresponding to the pathname will be looked
-up by walking the tree starting with the first component
-of the pathname and using that dentry along with the next
-component to look up the next level and so on. Since it
-is a frequent operation for workloads like multiuser
-environments and web servers, it is important to optimize
-this path.
-
-Prior to 2.5.10, dcache_lock was acquired in d_lookup and thus
-in every component during path look-up. Since 2.5.10 onwards,
-fast-walk algorithm changed this by holding the dcache_lock
-at the beginning and walking as many cached path component
-dentries as possible. This significantly decreases the number
-of acquisition of dcache_lock. However it also increases the
-lock hold time significantly and affects performance in large
-SMP machines. Since 2.5.62 kernel, dcache has been using
-a new locking model that uses RCU to make dcache look-up
-lock-free.
-
-The current dcache locking model is not very different from the existing
-dcache locking model. Prior to 2.5.62 kernel, dcache_lock
-protected the hash chain, d_child, d_alias, d_lru lists as well
-as d_inode and several other things like mount look-up. RCU-based
-changes affect only the way the hash chain is protected. For everything
-else the dcache_lock must be taken for both traversing as well as
-updating. The hash chain updates too take the dcache_lock.
-The significant change is the way d_lookup traverses the hash chain,
-it doesn't acquire the dcache_lock for this and rely on RCU to
-ensure that the dentry has not been *freed*.
-
-
-Dcache locking details
-----------------------
+Resources
+=========
+
+(Note some of these resources are not up-to-date with the latest kernel
+ version.)
+
+Creating Linux virtual filesystems. 2002
+    <http://lwn.net/Articles/13325/>
+
+The Linux Virtual File-system Layer by Neil Brown. 1999
+    <http://www.cse.unsw.edu.au/~neilb/oss/linux-commentary/vfs.html>
+
+A tour of the Linux VFS by Michael K. Johnson. 1996
+    <http://www.tldp.org/LDP/khg/HyperNews/get/fs/vfstour.html>
 
-For many multi-user workloads, open() and stat() on files are
-very frequently occurring operations. Both involve walking
-of path names to find the dentry corresponding to the
-concerned file. In 2.4 kernel, dcache_lock was held
-during look-up of each path component. Contention and
-cache-line bouncing of this global lock caused significant
-scalability problems. With the introduction of RCU
-in Linux kernel, this was worked around by making
-the look-up of path components during path walking lock-free.
-
-
-Safe lock-free look-up of dcache hash table
-===========================================
-
-Dcache is a complex data structure with the hash table entries
-also linked together in other lists. In 2.4 kernel, dcache_lock
-protected all the lists. We applied RCU only on hash chain
-walking. The rest of the lists are still protected by dcache_lock.
-Some of the important changes are :
-
-1. The deletion from hash chain is done using hlist_del_rcu() macro which
-   doesn't initialize next pointer of the deleted dentry and this
-   allows us to walk safely lock-free while a deletion is happening.
-
-2. Insertion of a dentry into the hash table is done using
-   hlist_add_head_rcu() which take care of ordering the writes -
-   the writes to the dentry must be visible before the dentry
-   is inserted. This works in conjunction with hlist_for_each_rcu()
-   while walking the hash chain. The only requirement is that
-   all initialization to the dentry must be done before hlist_add_head_rcu()
-   since we don't have dcache_lock protection while traversing
-   the hash chain. This isn't different from the existing code.
-
-3. The dentry looked up without holding dcache_lock by cannot be
-   returned for walking if it is unhashed. It then may have a NULL
-   d_inode or other bogosity since RCU doesn't protect the other
-   fields in the dentry. We therefore use a flag DCACHE_UNHASHED to
-   indicate unhashed  dentries and use this in conjunction with a
-   per-dentry lock (d_lock). Once looked up without the dcache_lock,
-   we acquire the per-dentry lock (d_lock) and check if the
-   dentry is unhashed. If so, the look-up is failed. If not, the
-   reference count of the dentry is increased and the dentry is returned.
-
-4. Once a dentry is looked up, it must be ensured during the path
-   walk for that component it doesn't go away. In pre-2.5.10 code,
-   this was done holding a reference to the dentry. dcache_rcu does
-   the same.  In some sense, dcache_rcu path walking looks like
-   the pre-2.5.10 version.
-
-5. All dentry hash chain updates must take the dcache_lock as well as
-   the per-dentry lock in that order. dput() does this to ensure
-   that a dentry that has just been looked up in another CPU
-   doesn't get deleted before dget() can be done on it.
-
-6. There are several ways to do reference counting of RCU protected
-   objects. One such example is in ipv4 route cache where
-   deferred freeing (using call_rcu()) is done as soon as
-   the reference count goes to zero. This cannot be done in
-   the case of dentries because tearing down of dentries
-   require blocking (dentry_iput()) which isn't supported from
-   RCU callbacks. Instead, tearing down of dentries happen
-   synchronously in dput(), but actual freeing happens later
-   when RCU grace period is over. This allows safe lock-free
-   walking of the hash chains, but a matched dentry may have
-   been partially torn down. The checking of DCACHE_UNHASHED
-   flag with d_lock held detects such dentries and prevents
-   them from being returned from look-up.
-
-
-Maintaining POSIX rename semantics
-==================================
-
-Since look-up of dentries is lock-free, it can race against
-a concurrent rename operation. For example, during rename
-of file A to B, look-up of either A or B must succeed.
-So, if look-up of B happens after A has been removed from the
-hash chain but not added to the new hash chain, it may fail.
-Also, a comparison while the name is being written concurrently
-by a rename may result in false positive matches violating
-rename semantics.  Issues related to race with rename are
-handled as described below :
-
-1. Look-up can be done in two ways - d_lookup() which is safe
-   from simultaneous renames and __d_lookup() which is not.
-   If __d_lookup() fails, it must be followed up by a d_lookup()
-   to correctly determine whether a dentry is in the hash table
-   or not. d_lookup() protects look-ups using a sequence
-   lock (rename_lock).
-
-2. The name associated with a dentry (d_name) may be changed if
-   a rename is allowed to happen simultaneously. To avoid memcmp()
-   in __d_lookup() go out of bounds due to a rename and false
-   positive comparison, the name comparison is done while holding the
-   per-dentry lock. This prevents concurrent renames during this
-   operation.
-
-3. Hash table walking during look-up may move to a different bucket as
-   the current dentry is moved to a different bucket due to rename.
-   But we use hlists in dcache hash table and they are null-terminated.
-   So, even if a dentry moves to a different bucket, hash chain
-   walk will terminate. [with a list_head list, it may not since
-   termination is when the list_head in the original bucket is reached].
-   Since we redo the d_parent check and compare name while holding
-   d_lock, lock-free look-up will not race against d_move().
-
-4. There can be a theoretical race when a dentry keeps coming back
-   to original bucket due to double moves. Due to this look-up may
-   consider that it has never moved and can end up in a infinite loop.
-   But this is not any worse that theoretical livelocks we already
-   have in the kernel.
-
-
-Important guidelines for filesystem developers related to dcache_rcu
-====================================================================
-
-1. Existing dcache interfaces (pre-2.5.62) exported to filesystem
-   don't change. Only dcache internal implementation changes. However
-   filesystems *must not* delete from the dentry hash chains directly
-   using the list macros like allowed earlier. They must use dcache
-   APIs like d_drop() or __d_drop() depending on the situation.
-
-2. d_flags is now protected by a per-dentry lock (d_lock). All
-   access to d_flags must be protected by it.
-
-3. For a hashed dentry, checking of d_count needs to be protected
-   by d_lock.
-
-
-Papers and other documentation on dcache locking
-================================================
-
-1. Scaling dcache with RCU (http://linuxjournal.com/article.php?sid=7124).
-
-2. http://lse.sourceforge.net/locking/dcache/dcache.html
+A small trail through the Linux kernel by Andries Brouwer. 2001
+    <http://www.win.tue.nl/~aeb/linux/vfs/trail.html>
diff --git a/Documentation/filesystems/xfs.txt b/Documentation/filesystems/xfs.txt
index c7d5d0c7067d..74aeb142ae5f 100644
--- a/Documentation/filesystems/xfs.txt
+++ b/Documentation/filesystems/xfs.txt
@@ -19,15 +19,43 @@ Mount Options
 
 When mounting an XFS filesystem, the following options are accepted.
 
-  biosize=size
-        Sets the preferred buffered I/O size (default size is 64K).
-        "size" must be expressed as the logarithm (base2) of the
-        desired I/O size.
-        Valid values for this option are 14 through 16, inclusive
-        (i.e. 16K, 32K, and 64K bytes).  On machines with a 4K
-        pagesize, 13 (8K bytes) is also a valid size.
-        The preferred buffered I/O size can also be altered on an
-        individual file basis using the ioctl(2) system call.
+  allocsize=size
+        Sets the buffered I/O end-of-file preallocation size when
+        doing delayed allocation writeout (default size is 64KiB).
+        Valid values for this option are page size (typically 4KiB)
+        through to 1GiB, inclusive, in power-of-2 increments.
+
+  attr2/noattr2
+        The options enable/disable (default is disabled for backward
+        compatibility on-disk) an "opportunistic" improvement to be
+        made in the way inline extended attributes are stored on-disk.
+        When the new form is used for the first time (by setting or
+        removing extended attributes) the on-disk superblock feature
+        bit field will be updated to reflect this format being in use.
+
+  barrier
+        Enables the use of block layer write barriers for writes into
+        the journal and unwritten extent conversion.  This allows for
+        drive level write caching to be enabled, for devices that
+        support write barriers.
+
+  dmapi
+        Enable the DMAPI (Data Management API) event callouts.
+        Use with the "mtpt" option.
+
+  grpid/bsdgroups and nogrpid/sysvgroups
+        These options define what group ID a newly created file gets.
+        When grpid is set, it takes the group ID of the directory in
+        which it is created; otherwise (the default) it takes the fsgid
+        of the current process, unless the directory has the setgid bit
+        set, in which case it takes the gid from the parent directory,
+        and also gets the setgid bit set if it is a directory itself.
+
+  ihashsize=value
+        Sets the number of hash buckets available for hashing the
+        in-memory inodes of the specified mount point.  If a value
+        of zero is used, the value selected by the default algorithm
+        will be displayed in /proc/mounts.
 
   ikeep/noikeep
         When inode clusters are emptied of inodes, keep them around
@@ -35,12 +63,31 @@ When mounting an XFS filesystem, the following options are accepted.
         and is still the default for now.  Using the noikeep option,
         inode clusters are returned to the free space pool.
 
+  inode64
+        Indicates that XFS is allowed to create inodes at any location
+        in the filesystem, including those which will result in inode
+        numbers occupying more than 32 bits of significance.  This is
+        provided for backwards compatibility, but causes problems for
+        backup applications that cannot handle large inode numbers.
+
+  largeio/nolargeio
+        If "nolargeio" is specified, the optimal I/O reported in
+        st_blksize by stat(2) will be as small as possible to allow user
+        applications to avoid inefficient read/modify/write I/O.
+        If "largeio" specified, a filesystem that has a "swidth" specified
+        will return the "swidth" value (in bytes) in st_blksize. If the
+        filesystem does not have a "swidth" specified but does specify
+        an "allocsize" then "allocsize" (in bytes) will be returned
+        instead.
+        If neither of these two options are specified, then filesystem
+        will behave as if "nolargeio" was specified.
+
   logbufs=value
         Set the number of in-memory log buffers.  Valid numbers range
         from 2-8 inclusive.
         The default value is 8 buffers for filesystems with a
-        blocksize of 64K, 4 buffers for filesystems with a blocksize
-        of 32K, 3 buffers for filesystems with a blocksize of 16K
+        blocksize of 64KiB, 4 buffers for filesystems with a blocksize
+        of 32KiB, 3 buffers for filesystems with a blocksize of 16KiB
         and 2 buffers for all other configurations.  Increasing the
         number of buffers may increase performance on some workloads
         at the cost of the memory used for the additional log buffers
@@ -49,10 +96,10 @@ When mounting an XFS filesystem, the following options are accepted.
   logbsize=value
         Set the size of each in-memory log buffer.
         Size may be specified in bytes, or in kilobytes with a "k" suffix.
-        Valid sizes for version 1 and version 2 logs are 16384 (16k) and 
-        32768 (32k).  Valid sizes for version 2 logs also include 
+        Valid sizes for version 1 and version 2 logs are 16384 (16k) and
+        32768 (32k).  Valid sizes for version 2 logs also include
         65536 (64k), 131072 (128k) and 262144 (256k).
-        The default value for machines with more than 32MB of memory
+        The default value for machines with more than 32MiB of memory
         is 32768, machines with less memory use 16384 by default.
 
   logdev=device and rtdev=device
@@ -62,6 +109,11 @@ When mounting an XFS filesystem, the following options are accepted.
         optional, and the log section can be separate from the data
         section or contained within it.
 
+  mtpt=mountpoint
+        Use with the "dmapi" option.  The value specified here will be
+        included in the DMAPI mount event, and should be the path of
+        the actual mountpoint that is used.
+
   noalign
         Data allocations will not be aligned at stripe unit boundaries.
 
@@ -91,13 +143,17 @@ When mounting an XFS filesystem, the following options are accepted.
         O_SYNC writes can be lost if the system crashes.
         If timestamp updates are critical, use the osyncisosync option.
 
-  quota/usrquota/uqnoenforce
+  uquota/usrquota/uqnoenforce/quota
         User disk quota accounting enabled, and limits (optionally)
-        enforced.
+        enforced.  Refer to xfs_quota(8) for further details.
 
-  grpquota/gqnoenforce
+  gquota/grpquota/gqnoenforce
         Group disk quota accounting enabled and limits (optionally)
-        enforced.
+        enforced.  Refer to xfs_quota(8) for further details.
+
+  pquota/prjquota/pqnoenforce
+        Project disk quota accounting enabled and limits (optionally)
+        enforced.  Refer to xfs_quota(8) for further details.
 
   sunit=value and swidth=value
         Used to specify the stripe unit and width for a RAID device or
@@ -113,15 +169,21 @@ When mounting an XFS filesystem, the following options are accepted.
         The "swidth" option is required if the "sunit" option has been
         specified, and must be a multiple of the "sunit" value.
 
+  swalloc
+        Data allocations will be rounded up to stripe width boundaries
+        when the current end of file is being extended and the file
+        size is larger than the stripe width size.
+
+
 sysctls
 =======
 
 The following sysctls are available for the XFS filesystem:
 
   fs.xfs.stats_clear            (Min: 0  Default: 0  Max: 1)
-        Setting this to "1" clears accumulated XFS statistics 
+        Setting this to "1" clears accumulated XFS statistics
         in /proc/fs/xfs/stat.  It then immediately resets to "0".
-  
+
   fs.xfs.xfssyncd_centisecs     (Min: 100  Default: 3000  Max: 720000)
         The interval at which the xfssyncd thread flushes metadata
         out to disk.  This thread will flush log activity out, and
@@ -143,9 +205,9 @@ The following sysctls are available for the XFS filesystem:
                 XFS_ERRLEVEL_HIGH:      5
 
   fs.xfs.panic_mask             (Min: 0  Default: 0  Max: 127)
-        Causes certain error conditions to call BUG(). Value is a bitmask; 
+        Causes certain error conditions to call BUG(). Value is a bitmask;
         AND together the tags which represent errors which should cause panics:
-        
+
                 XFS_NO_PTAG                     0
                 XFS_PTAG_IFLUSH                 0x00000001
                 XFS_PTAG_LOGRES                 0x00000002
@@ -155,7 +217,7 @@ The following sysctls are available for the XFS filesystem:
                 XFS_PTAG_SHUTDOWN_IOERROR       0x00000020
                 XFS_PTAG_SHUTDOWN_LOGERROR      0x00000040
 
-        This option is intended for debugging only.             
+        This option is intended for debugging only.
 
   fs.xfs.irix_symlink_mode      (Min: 0  Default: 0  Max: 1)
         Controls whether symlinks are created with mode 0777 (default)
@@ -164,25 +226,37 @@ The following sysctls are available for the XFS filesystem:
   fs.xfs.irix_sgid_inherit      (Min: 0  Default: 0  Max: 1)
         Controls files created in SGID directories.
         If the group ID of the new file does not match the effective group
-        ID or one of the supplementary group IDs of the parent dir, the 
-        ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl 
+        ID or one of the supplementary group IDs of the parent dir, the
+        ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl
         is set.
 
   fs.xfs.restrict_chown         (Min: 0  Default: 1  Max: 1)
         Controls whether unprivileged users can use chown to "give away"
         a file to another user.
 
-  fs.xfs.inherit_sync           (Min: 0  Default: 1  Max 1)
-        Setting this to "1" will cause the "sync" flag set 
-        by the chattr(1) command on a directory to be
+  fs.xfs.inherit_sync           (Min: 0  Default: 1  Max: 1)
+        Setting this to "1" will cause the "sync" flag set
+        by the xfs_io(8) chattr command on a directory to be
         inherited by files in that directory.
 
-  fs.xfs.inherit_nodump         (Min: 0  Default: 1  Max 1)
-        Setting this to "1" will cause the "nodump" flag set 
-        by the chattr(1) command on a directory to be
+  fs.xfs.inherit_nodump         (Min: 0  Default: 1  Max: 1)
+        Setting this to "1" will cause the "nodump" flag set
+        by the xfs_io(8) chattr command on a directory to be
         inherited by files in that directory.
 
-  fs.xfs.inherit_noatime        (Min: 0  Default: 1  Max 1)
-        Setting this to "1" will cause the "noatime" flag set 
-        by the chattr(1) command on a directory to be
+  fs.xfs.inherit_noatime        (Min: 0  Default: 1  Max: 1)
+        Setting this to "1" will cause the "noatime" flag set
+        by the xfs_io(8) chattr command on a directory to be
         inherited by files in that directory.
+
+  fs.xfs.inherit_nosymlinks     (Min: 0  Default: 1  Max: 1)
+        Setting this to "1" will cause the "nosymlinks" flag set
+        by the xfs_io(8) chattr command on a directory to be
+        inherited by files in that directory.
+
+  fs.xfs.rotorstep              (Min: 1  Default: 1  Max: 256)
+        In "inode32" allocation mode, this option determines how many
+        files the allocator attempts to allocate in the same allocation
+        group before moving to the next allocation group.  The intent
+        is to control the rate at which the allocator moves between
+        allocation groups when allocating extents for new files.