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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 /include/linux/nfs_fs_sb.h
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 'include/linux/nfs_fs_sb.h')
-rw-r--r--include/linux/nfs_fs_sb.h21
1 files changed, 9 insertions, 12 deletions
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index d404ceca9168..6d0be0efd1b5 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -51,7 +51,6 @@ struct nfs_client {
51 unsigned long cl_lease_time; 51 unsigned long cl_lease_time;
52 unsigned long cl_last_renewal; 52 unsigned long cl_last_renewal;
53 struct work_struct cl_renewd; 53 struct work_struct cl_renewd;
54 struct work_struct cl_recoverd;
55 54
56 struct rpc_wait_queue cl_rpcwaitq; 55 struct rpc_wait_queue cl_rpcwaitq;
57 56
@@ -74,6 +73,10 @@ struct nfs_client {
74 */ 73 */
75struct nfs_server { 74struct nfs_server {
76 struct nfs_client * nfs_client; /* shared client and NFS4 state */ 75 struct nfs_client * nfs_client; /* shared client and NFS4 state */
76 struct list_head client_link; /* List of other nfs_server structs
77 * that share the same client
78 */
79 struct list_head master_link; /* link in master servers list */
77 struct rpc_clnt * client; /* RPC client handle */ 80 struct rpc_clnt * client; /* RPC client handle */
78 struct rpc_clnt * client_acl; /* ACL RPC client handle */ 81 struct rpc_clnt * client_acl; /* ACL RPC client handle */
79 struct nfs_iostats * io_stats; /* I/O statistics */ 82 struct nfs_iostats * io_stats; /* I/O statistics */
@@ -92,20 +95,13 @@ struct nfs_server {
92 unsigned int acdirmin; 95 unsigned int acdirmin;
93 unsigned int acdirmax; 96 unsigned int acdirmax;
94 unsigned int namelen; 97 unsigned int namelen;
95 char * hostname; /* remote hostname */ 98
96 struct nfs_fh fh;
97 struct sockaddr_in addr;
98 struct nfs_fsid fsid; 99 struct nfs_fsid fsid;
100 __u64 maxfilesize; /* maximum file size */
99 unsigned long mount_time; /* when this fs was mounted */ 101 unsigned long mount_time; /* when this fs was mounted */
102 dev_t s_dev; /* superblock dev numbers */
103
100#ifdef CONFIG_NFS_V4 104#ifdef CONFIG_NFS_V4
101 /* Our own IP address, as a null-terminated string.
102 * This is used to generate the clientid, and the callback address.
103 */
104 char ip_addr[16];
105 char * mnt_path;
106 struct list_head nfs4_siblings; /* List of other nfs_server structs
107 * that share the same clientid
108 */
109 u32 attr_bitmask[2];/* V4 bitmask representing the set 105 u32 attr_bitmask[2];/* V4 bitmask representing the set
110 of attributes supported on this 106 of attributes supported on this
111 filesystem */ 107 filesystem */
@@ -113,6 +109,7 @@ struct nfs_server {
113 that are supported on this 109 that are supported on this
114 filesystem */ 110 filesystem */
115#endif 111#endif
112 void (*destroy)(struct nfs_server *);
116}; 113};
117 114
118/* Server capabilities */ 115/* Server capabilities */