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authorDavid Howells <dhowells@redhat.com>2006-08-22 20:06:13 -0400
committerTrond Myklebust <Trond.Myklebust@netapp.com>2006-09-22 23:24:37 -0400
commit54ceac4515986030c2502960be620198dd8fe25b (patch)
treeb4ae4305c5652c0fe883ef5ea3243da91dbd2b34 /fs/nfs/namespace.c
parentcf6d7b5de8535a9f0088c5cc28ee2dae87371b4a (diff)
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>
Diffstat (limited to 'fs/nfs/namespace.c')
-rw-r--r--fs/nfs/namespace.c25
1 files changed, 18 insertions, 7 deletions
diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index d8b8d56266cb..77b00684894d 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -2,6 +2,7 @@
2 * linux/fs/nfs/namespace.c 2 * linux/fs/nfs/namespace.c
3 * 3 *
4 * Copyright (C) 2005 Trond Myklebust <Trond.Myklebust@netapp.com> 4 * Copyright (C) 2005 Trond Myklebust <Trond.Myklebust@netapp.com>
5 * - Modified by David Howells <dhowells@redhat.com>
5 * 6 *
6 * NFS namespace 7 * NFS namespace
7 */ 8 */
@@ -28,6 +29,7 @@ int nfs_mountpoint_expiry_timeout = 500 * HZ;
28/* 29/*
29 * nfs_path - reconstruct the path given an arbitrary dentry 30 * nfs_path - reconstruct the path given an arbitrary dentry
30 * @base - arbitrary string to prepend to the path 31 * @base - arbitrary string to prepend to the path
32 * @droot - pointer to root dentry for mountpoint
31 * @dentry - pointer to dentry 33 * @dentry - pointer to dentry
32 * @buffer - result buffer 34 * @buffer - result buffer
33 * @buflen - length of buffer 35 * @buflen - length of buffer
@@ -38,7 +40,9 @@ int nfs_mountpoint_expiry_timeout = 500 * HZ;
38 * This is mainly for use in figuring out the path on the 40 * This is mainly for use in figuring out the path on the
39 * server side when automounting on top of an existing partition. 41 * server side when automounting on top of an existing partition.
40 */ 42 */
41char *nfs_path(const char *base, const struct dentry *dentry, 43char *nfs_path(const char *base,
44 const struct dentry *droot,
45 const struct dentry *dentry,
42 char *buffer, ssize_t buflen) 46 char *buffer, ssize_t buflen)
43{ 47{
44 char *end = buffer+buflen; 48 char *end = buffer+buflen;
@@ -47,7 +51,7 @@ char *nfs_path(const char *base, const struct dentry *dentry,
47 *--end = '\0'; 51 *--end = '\0';
48 buflen--; 52 buflen--;
49 spin_lock(&dcache_lock); 53 spin_lock(&dcache_lock);
50 while (!IS_ROOT(dentry)) { 54 while (!IS_ROOT(dentry) && dentry != droot) {
51 namelen = dentry->d_name.len; 55 namelen = dentry->d_name.len;
52 buflen -= namelen + 1; 56 buflen -= namelen + 1;
53 if (buflen < 0) 57 if (buflen < 0)
@@ -96,12 +100,13 @@ static void * nfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
96 struct nfs_fattr fattr; 100 struct nfs_fattr fattr;
97 int err; 101 int err;
98 102
103 dprintk("--> nfs_follow_mountpoint()\n");
104
99 BUG_ON(IS_ROOT(dentry)); 105 BUG_ON(IS_ROOT(dentry));
100 dprintk("%s: enter\n", __FUNCTION__); 106 dprintk("%s: enter\n", __FUNCTION__);
101 dput(nd->dentry); 107 dput(nd->dentry);
102 nd->dentry = dget(dentry); 108 nd->dentry = dget(dentry);
103 if (d_mountpoint(nd->dentry)) 109
104 goto out_follow;
105 /* Look it up again */ 110 /* Look it up again */
106 parent = dget_parent(nd->dentry); 111 parent = dget_parent(nd->dentry);
107 err = server->nfs_client->rpc_ops->lookup(parent->d_inode, 112 err = server->nfs_client->rpc_ops->lookup(parent->d_inode,
@@ -134,6 +139,8 @@ static void * nfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
134 schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout); 139 schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
135out: 140out:
136 dprintk("%s: done, returned %d\n", __FUNCTION__, err); 141 dprintk("%s: done, returned %d\n", __FUNCTION__, err);
142
143 dprintk("<-- nfs_follow_mountpoint() = %d\n", err);
137 return ERR_PTR(err); 144 return ERR_PTR(err);
138out_err: 145out_err:
139 path_release(nd); 146 path_release(nd);
@@ -183,14 +190,14 @@ static struct vfsmount *nfs_do_clone_mount(struct nfs_server *server,
183 switch (server->nfs_client->cl_nfsversion) { 190 switch (server->nfs_client->cl_nfsversion) {
184 case 2: 191 case 2:
185 case 3: 192 case 3:
186 mnt = vfs_kern_mount(&clone_nfs_fs_type, 0, devname, mountdata); 193 mnt = vfs_kern_mount(&nfs_xdev_fs_type, 0, devname, mountdata);
187 break; 194 break;
188 case 4: 195 case 4:
189 mnt = vfs_kern_mount(&clone_nfs4_fs_type, 0, devname, mountdata); 196 mnt = vfs_kern_mount(&nfs4_xdev_fs_type, 0, devname, mountdata);
190 } 197 }
191 return mnt; 198 return mnt;
192#else 199#else
193 return vfs_kern_mount(&clone_nfs_fs_type, 0, devname, mountdata); 200 return vfs_kern_mount(&nfs_xdev_fs_type, 0, devname, mountdata);
194#endif 201#endif
195} 202}
196 203
@@ -216,6 +223,8 @@ struct vfsmount *nfs_do_submount(const struct vfsmount *mnt_parent,
216 char *page = (char *) __get_free_page(GFP_USER); 223 char *page = (char *) __get_free_page(GFP_USER);
217 char *devname; 224 char *devname;
218 225
226 dprintk("--> nfs_do_submount()\n");
227
219 dprintk("%s: submounting on %s/%s\n", __FUNCTION__, 228 dprintk("%s: submounting on %s/%s\n", __FUNCTION__,
220 dentry->d_parent->d_name.name, 229 dentry->d_parent->d_name.name,
221 dentry->d_name.name); 230 dentry->d_name.name);
@@ -230,5 +239,7 @@ free_page:
230 free_page((unsigned long)page); 239 free_page((unsigned long)page);
231out: 240out:
232 dprintk("%s: done\n", __FUNCTION__); 241 dprintk("%s: done\n", __FUNCTION__);
242
243 dprintk("<-- nfs_do_submount() = %p\n", mnt);
233 return mnt; 244 return mnt;
234} 245}