linux/fs
David Howells 54ceac4515 NFS: Share NFS superblocks per-protocol per-server per-FSID
The attached patch makes NFS share superblocks between mounts from the same
server and FSID over the same protocol.

It does this by creating each superblock with a false root and returning the
real root dentry in the vfsmount presented by get_sb(). The root dentry set
starts off as an anonymous dentry if we don't already have the dentry for its
inode, otherwise it simply returns the dentry we already have.

We may thus end up with several trees of dentries in the superblock, and if at
some later point one of anonymous tree roots is discovered by normal filesystem
activity to be located in another tree within the superblock, the anonymous
root is named and materialises attached to the second tree at the appropriate
point.

Why do it this way? Why not pass an extra argument to the mount() syscall to
indicate the subpath and then pathwalk from the server root to the desired
directory? You can't guarantee this will work for two reasons:

 (1) The root and intervening nodes may not be accessible to the client.

     With NFS2 and NFS3, for instance, mountd is called on the server to get
     the filehandle for the tip of a path. mountd won't give us handles for
     anything we don't have permission to access, and so we can't set up NFS
     inodes for such nodes, and so can't easily set up dentries (we'd have to
     have ghost inodes or something).

     With this patch we don't actually create dentries until we get handles
     from the server that we can use to set up their inodes, and we don't
     actually bind them into the tree until we know for sure where they go.

 (2) Inaccessible symbolic links.

     If we're asked to mount two exports from the server, eg:

	mount warthog:/warthog/aaa/xxx /mmm
	mount warthog:/warthog/bbb/yyy /nnn

     We may not be able to access anything nearer the root than xxx and yyy,
     but we may find out later that /mmm/www/yyy, say, is actually the same
     directory as the one mounted on /nnn. What we might then find out, for
     example, is that /warthog/bbb was actually a symbolic link to
     /warthog/aaa/xxx/www, but we can't actually determine that by talking to
     the server until /warthog is made available by NFS.

     This would lead to having constructed an errneous dentry tree which we
     can't easily fix. We can end up with a dentry marked as a directory when
     it should actually be a symlink, or we could end up with an apparently
     hardlinked directory.

     With this patch we need not make assumptions about the type of a dentry
     for which we can't retrieve information, nor need we assume we know its
     place in the grand scheme of things until we actually see that place.

This patch reduces the possibility of aliasing in the inode and page caches for
inodes that may be accessed by more than one NFS export. It also reduces the
number of superblocks required for NFS where there are many NFS exports being
used from a server (home directory server + autofs for example).

This in turn makes it simpler to do local caching of network filesystems, as it
can then be guaranteed that there won't be links from multiple inodes in
separate superblocks to the same cache file.

Obviously, cache aliasing between different levels of NFS protocol could still
be a problem, but at least that gives us another key to use when indexing the
cache.

This patch makes the following changes:

 (1) The server record construction/destruction has been abstracted out into
     its own set of functions to make things easier to get right.  These have
     been moved into fs/nfs/client.c.

     All the code in fs/nfs/client.c has to do with the management of
     connections to servers, and doesn't touch superblocks in any way; the
     remaining code in fs/nfs/super.c has to do with VFS superblock management.

 (2) The sequence of events undertaken by NFS mount is now reordered:

     (a) A volume representation (struct nfs_server) is allocated.

     (b) A server representation (struct nfs_client) is acquired.  This may be
     	 allocated or shared, and is keyed on server address, port and NFS
     	 version.

     (c) If allocated, the client representation is initialised.  The state
     	 member variable of nfs_client is used to prevent a race during
     	 initialisation from two mounts.

     (d) For NFS4 a simple pathwalk is performed, walking from FH to FH to find
     	 the root filehandle for the mount (fs/nfs/getroot.c).  For NFS2/3 we
     	 are given the root FH in advance.

     (e) The volume FSID is probed for on the root FH.

     (f) The volume representation is initialised from the FSINFO record
     	 retrieved on the root FH.

     (g) sget() is called to acquire a superblock.  This may be allocated or
     	 shared, keyed on client pointer and FSID.

     (h) If allocated, the superblock is initialised.

     (i) If the superblock is shared, then the new nfs_server record is
     	 discarded.

     (j) The root dentry for this mount is looked up from the root FH.

     (k) The root dentry for this mount is assigned to the vfsmount.

 (3) nfs_readdir_lookup() creates dentries for each of the entries readdir()
     returns; this function now attaches disconnected trees from alternate
     roots that happen to be discovered attached to a directory being read (in
     the same way nfs_lookup() is made to do for lookup ops).

     The new d_materialise_unique() function is now used to do this, thus
     permitting the whole thing to be done under one set of locks, and thus
     avoiding any race between mount and lookup operations on the same
     directory.

 (4) The client management code uses a new debug facility: NFSDBG_CLIENT which
     is set by echoing 1024 to /proc/net/sunrpc/nfs_debug.

 (5) Clone mounts are now called xdev mounts.

 (6) Use the dentry passed to the statfs() op as the handle for retrieving fs
     statistics rather than the root dentry of the superblock (which is now a
     dummy).

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
2006-09-22 23:24:37 -04:00
..
9p [PATCH] 9p: fix fid behavior on failed remove 2006-07-31 13:28:44 -07:00
adfs [PATCH] adfs error message fix 2006-08-14 12:54:28 -07:00
affs [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
afs [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
autofs [PATCH] VFS: Permit filesystem to override root dentry on mount 2006-06-23 07:42:45 -07:00
autofs4 [PATCH] fs: use list_move() 2006-06-26 09:58:18 -07:00
befs [PATCH] Fix BeFS slab corruption 2006-08-06 08:57:48 -07:00
bfs [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
cifs [CIFS] statfs for cifs unix extensions no longer experimental 2006-09-22 01:14:52 +00:00
coda [PATCH] Remove incorrect unlock_kernel from allocation failure path in coda_open() 2006-07-31 13:28:41 -07:00
configfs configfs: Prevent duplicate subsystem names. 2006-09-20 15:46:14 -07:00
cramfs [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
debugfs Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
devpts [PATCH] VFS: Permit filesystem to override root dentry on mount 2006-06-23 07:42:45 -07:00
efs [PATCH] efs: Remove incorrect unlock_kernel from failure path in efs_symlink_readpage() 2006-07-31 13:28:41 -07:00
exportfs [PATCH] NFS server subtree_check returns dubious value 2006-05-21 12:59:16 -07:00
ext2 [PATCH] EXT2: Remove superblock lock contention in ext2_statfs 2006-09-19 07:59:59 -07:00
ext3 [PATCH] ext3 sequential read regression fix 2006-09-16 12:54:32 -07:00
fat [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
freevxfs [PATCH] freevxfs: Add missing lock_kernel() to vxfs_readdir 2006-07-31 13:28:44 -07:00
fuse [PATCH] fuse: fix error case in fuse_readpages 2006-08-14 12:54:29 -07:00
hfs Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
hfsplus Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
hostfs [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
hpfs [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
hppfs [PATCH] VFS: Permit filesystem to perform statfs with a known root dentry 2006-06-23 07:42:45 -07:00
hugetlbfs [PATCH] mmap zero-length hugetlb file with PROT_NONE to protect a hugetlb virtual area 2006-07-10 13:24:21 -07:00
isofs Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
jbd [PATCH] manage-jbd-its-own-slab fix 2006-09-01 11:39:10 -07:00
jffs Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
jffs2 [JFFS2] Remove unneeded ifdefs from jffs2_fs_i.h 2006-09-22 10:13:46 +01:00
jfs JFS: Fix bug in quota code. tmp_bh.b_size must be initialized 2006-07-28 08:46:05 -05:00
lockd LOCKD: Fix a deadlock in nlm_traverse_files() 2006-08-24 15:51:00 -04:00
minix [PATCH] Fix for minix crash 2006-08-27 11:01:30 -07:00
msdos [PATCH] VFS: Permit filesystem to override root dentry on mount 2006-06-23 07:42:45 -07:00
ncpfs Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial 2006-06-30 15:39:30 -07:00
nfs NFS: Share NFS superblocks per-protocol per-server per-FSID 2006-09-22 23:24:37 -04:00
nfs_common [PATCH] nfsacl: Solaris VxFS compatibility fix 2005-10-11 09:46:54 -07:00
nfsd [CRYPTO] users: Use crypto_hash interface instead of crypto_digest 2006-09-21 11:46:21 +10:00
nls Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
ntfs [PATCH] lockdep: annotate NTFS locking rules 2006-07-03 15:27:08 -07:00
ocfs2 ocfs2: Remove overzealous BUG_ON() 2006-09-20 16:00:54 -07:00
openpromfs [OPENPROMFS]: Rewrite using in-kernel device tree and seq_file. 2006-06-25 23:19:14 -07:00
partitions [DISKLABEL] SUN: Fix signed int usage for sector count 2006-08-26 17:55:55 -07:00
proc [PATCH] /proc/meminfo: don't put spaces in names 2006-08-27 11:01:33 -07:00
qnx4 Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
ramfs [PATCH] NOMMU: Fix execution off of ramfs with mmap() 2006-07-10 13:24:21 -07:00
reiserfs [PATCH] lockdep: annotate reiserfs 2006-08-27 11:01:32 -07:00
romfs [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
smbfs Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
sysfs [PATCH] lockdep: annotate the sysfs i_mutex to be a separate class 2006-07-12 12:52:54 -07:00
sysv [PATCH] mark address_space_operations const 2006-06-28 14:59:04 -07:00
udf Fix possible UDF deadlock and memory corruption (CVE-2006-4145) 2006-08-22 12:52:23 -07:00
ufs [PATCH] ufs: truncate correction 2006-08-27 11:01:31 -07:00
vfat [PATCH] VFS: Permit filesystem to override root dentry on mount 2006-06-23 07:42:45 -07:00
xfs [XFS] Fix a bad pointer dereference in the quota statvfs handling. 2006-09-07 14:27:23 +10:00
aio.c spelling fixes 2006-06-26 18:35:02 +02:00
attr.c [PATCH] capable/capability.h (fs/) 2006-01-11 18:42:13 -08:00
bad_inode.c [PATCH] Make most file operations structs in fs/ const 2006-03-28 09:16:06 -08:00
binfmt_aout.c [PATCH] dump_thread() cleanup 2006-01-10 08:01:25 -08:00
binfmt_elf_fdpic.c [PATCH] FDPIC: Add coredump capability for the ELF-FDPIC binfmt 2006-07-10 13:24:22 -07:00
binfmt_elf.c [PATCH] FDPIC: Move roundup() into linux/kernel.h 2006-07-10 13:24:22 -07:00
binfmt_em86.c
binfmt_flat.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
binfmt_misc.c Merge branch 'master' of /home/trondmy/kernel/linux-2.6/ 2006-06-24 13:07:53 -04:00
binfmt_script.c
binfmt_som.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
bio.c [PATCH] Fix missing ret assignment in __bio_map_user() error path 2006-06-17 10:52:12 -07:00
block_dev.c [PATCH] lockdep: fix blkdev_open() warning 2006-08-27 11:01:29 -07:00
buffer.c [PATCH] invalidate_bdev() speedup 2006-07-31 13:28:38 -07:00
char_dev.c [PATCH] add function documentation for register_chrdev() 2006-07-14 21:53:54 -07:00
compat_ioctl.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
compat.c [PATCH] x86_64: Add compat_printk and sysctl to turn off compat layer warnings 2006-06-26 10:48:16 -07:00
dcache.c NFS: Add dentry materialisation op 2006-09-22 23:24:30 -04:00
dcookies.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
direct-io.c [PATCH] lockdep: annotate direct io 2006-07-03 15:27:06 -07:00
dnotify.c [PATCH] Use __read_mostly on some hot fs variables 2006-03-26 08:56:56 -08:00
dquot.c [PATCH] use list_add_tail() instead of list_add() 2006-06-26 09:58:17 -07:00
drop_caches.c [PATCH] drop-pagecache 2006-01-08 20:12:40 -08:00
eventpoll.c [PATCH] eventpoll.c compile fix 2006-08-27 11:01:31 -07:00
exec.c [PATCH] fix up lockdep trace in fs/exec.c 2006-08-27 11:01:32 -07:00
fcntl.c BUG_ON() Conversion in fs/fcntl.c 2006-04-02 13:37:19 +02:00
fifo.c [PATCH] pipe.c/fifo.c code cleanups 2006-04-11 13:53:33 +02:00
file_table.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
file.c [PATCH] alloc_fdtable() expansion fix 2006-07-12 12:52:55 -07:00
filesystems.c [PATCH] fix missing includes 2005-10-30 17:37:32 -08:00
fs-writeback.c [PATCH] zoned vm counters: conversion of nr_unstable to per zone counter 2006-06-30 11:25:36 -07:00
inode.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial 2006-06-30 15:39:30 -07:00
inotify_user.c [PATCH] inotify: fix deadlock found by lockdep 2006-07-31 13:28:41 -07:00
inotify.c [PATCH] inotify (4/5): allow watch removal from event handler 2006-06-20 05:25:19 -04:00
ioctl.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
ioprio.c [PATCH] uninline ioprio_best() 2006-08-21 10:02:50 +02:00
Kconfig ocfs2: Remove EXPERIMENTAL dependency 2006-09-20 16:00:06 -07:00
Kconfig.binfmt [PATCH] frv: suppress configuration of certain features for FRV 2006-01-08 20:13:36 -08:00
libfs.c [PATCH] core: use list_move() 2006-06-26 09:58:17 -07:00
locks.c [PATCH] fcntl(F_SETSIG) fix 2006-08-14 13:10:59 -07:00
Makefile [PATCH] devfs: Remove devfs from the kernel tree 2006-06-26 12:25:05 -07:00
mbcache.c [PATCH] Typo fixes 2006-03-28 09:16:08 -08:00
mpage.c [PATCH] writeback: fix range handling 2006-06-23 07:42:49 -07:00
namei.c VFS: Fix access("file", X_OK) in the presence of ACLs 2006-08-24 15:54:58 -04:00
namespace.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
nfsctl.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
open.c [PATCH] ftruncate does not always update m/ctime 2006-06-25 10:01:15 -07:00
pipe.c [PATCH] VFS: Permit filesystem to override root dentry on mount 2006-06-23 07:42:45 -07:00
pnode.c [PATCH] core: use list_move() 2006-06-26 09:58:17 -07:00
pnode.h [PATCH] unbindable mounts 2005-11-07 18:18:11 -08:00
posix_acl.c [PATCH] gfp flags annotations - part 1 2005-10-08 15:00:57 -07:00
quota_v1.c
quota_v2.c [PATCH] sem2mutex: quota 2006-03-23 07:38:11 -08:00
quota.c [PATCH] sem2mutex: quota 2006-03-23 07:38:11 -08:00
read_write.c [PATCH] fs/read_write.c: EXPORT_UNUSED_SYMBOL 2006-07-10 13:24:18 -07:00
readdir.c [PATCH] mutex subsystem, semaphore to mutex: VFS, ->i_sem 2006-01-09 15:59:24 -08:00
select.c [PATCH] fs: sys_poll with timeout -1 bug fix 2006-06-25 10:01:22 -07:00
seq_file.c [PATCH] sem2mutex: fs/seq_file.c 2006-03-23 07:38:12 -08:00
splice.c [PATCH] splice: fix problems with sys_tee() 2006-07-10 11:00:01 +02:00
stat.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
super.c [PATCH] add missing desctiption in super.c 2006-09-06 11:00:01 -07:00
sync.c [PATCH] writeback: fix range handling 2006-06-23 07:42:49 -07:00
xattr_acl.c
xattr.c [PATCH] log more info for directory entry change events 2006-06-20 05:25:28 -04:00