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| Original file line number | Diff line number | Diff line change |
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| The NFS client | ||
| ============== | ||
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| The NFS version 2 protocol was first documented in RFC1094 (March 1989). | ||
| Since then two more major releases of NFS have been published, with NFSv3 | ||
| being documented in RFC1813 (June 1995), and NFSv4 in RFC3530 (April | ||
| 2003). | ||
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| The Linux NFS client currently supports all the above published versions, | ||
| and work is in progress on adding support for minor version 1 of the NFSv4 | ||
| protocol. | ||
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| The purpose of this document is to provide information on some of the | ||
| upcall interfaces that are used in order to provide the NFS client with | ||
| some of the information that it requires in order to fully comply with | ||
| the NFS spec. | ||
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| The DNS resolver | ||
| ================ | ||
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| NFSv4 allows for one server to refer the NFS client to data that has been | ||
| migrated onto another server by means of the special "fs_locations" | ||
| attribute. See | ||
| http://tools.ietf.org/html/rfc3530#section-6 | ||
| and | ||
| http://tools.ietf.org/html/draft-ietf-nfsv4-referrals-00 | ||
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| The fs_locations information can take the form of either an ip address and | ||
| a path, or a DNS hostname and a path. The latter requires the NFS client to | ||
| do a DNS lookup in order to mount the new volume, and hence the need for an | ||
| upcall to allow userland to provide this service. | ||
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| Assuming that the user has the 'rpc_pipefs' filesystem mounted in the usual | ||
| /var/lib/nfs/rpc_pipefs, the upcall consists of the following steps: | ||
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| (1) The process checks the dns_resolve cache to see if it contains a | ||
| valid entry. If so, it returns that entry and exits. | ||
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| (2) If no valid entry exists, the helper script '/sbin/nfs_cache_getent' | ||
| (may be changed using the 'nfs.cache_getent' kernel boot parameter) | ||
| is run, with two arguments: | ||
| - the cache name, "dns_resolve" | ||
| - the hostname to resolve | ||
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| (3) After looking up the corresponding ip address, the helper script | ||
| writes the result into the rpc_pipefs pseudo-file | ||
| '/var/lib/nfs/rpc_pipefs/cache/dns_resolve/channel' | ||
| in the following (text) format: | ||
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| "<ip address> <hostname> <ttl>\n" | ||
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| Where <ip address> is in the usual IPv4 (123.456.78.90) or IPv6 | ||
| (ffee:ddcc:bbaa:9988:7766:5544:3322:1100, ffee::1100, ...) format. | ||
| <hostname> is identical to the second argument of the helper | ||
| script, and <ttl> is the 'time to live' of this cache entry (in | ||
| units of seconds). | ||
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| Note: If <ip address> is invalid, say the string "0", then a negative | ||
| entry is created, which will cause the kernel to treat the hostname | ||
| as having no valid DNS translation. | ||
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| A basic sample /sbin/nfs_cache_getent | ||
| ===================================== | ||
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| #!/bin/bash | ||
| # | ||
| ttl=600 | ||
| # | ||
| cut=/usr/bin/cut | ||
| getent=/usr/bin/getent | ||
| rpc_pipefs=/var/lib/nfs/rpc_pipefs | ||
| # | ||
| die() | ||
| { | ||
| echo "Usage: $0 cache_name entry_name" | ||
| exit 1 | ||
| } | ||
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| [ $# -lt 2 ] && die | ||
| cachename="$1" | ||
| cache_path=${rpc_pipefs}/cache/${cachename}/channel | ||
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| case "${cachename}" in | ||
| dns_resolve) | ||
| name="$2" | ||
| result="$(${getent} hosts ${name} | ${cut} -f1 -d\ )" | ||
| [ -z "${result}" ] && result="0" | ||
| ;; | ||
| *) | ||
| die | ||
| ;; | ||
| esac | ||
| echo "${result} ${name} ${ttl}" >${cache_path} | ||
|
|
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,140 @@ | ||
| /* | ||
| * linux/fs/nfs/cache_lib.c | ||
| * | ||
| * Helper routines for the NFS client caches | ||
| * | ||
| * Copyright (c) 2009 Trond Myklebust <Trond.Myklebust@netapp.com> | ||
| */ | ||
| #include <linux/kmod.h> | ||
| #include <linux/module.h> | ||
| #include <linux/moduleparam.h> | ||
| #include <linux/mount.h> | ||
| #include <linux/namei.h> | ||
| #include <linux/sunrpc/cache.h> | ||
| #include <linux/sunrpc/rpc_pipe_fs.h> | ||
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| #include "cache_lib.h" | ||
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| #define NFS_CACHE_UPCALL_PATHLEN 256 | ||
| #define NFS_CACHE_UPCALL_TIMEOUT 15 | ||
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| static char nfs_cache_getent_prog[NFS_CACHE_UPCALL_PATHLEN] = | ||
| "/sbin/nfs_cache_getent"; | ||
| static unsigned long nfs_cache_getent_timeout = NFS_CACHE_UPCALL_TIMEOUT; | ||
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| module_param_string(cache_getent, nfs_cache_getent_prog, | ||
| sizeof(nfs_cache_getent_prog), 0600); | ||
| MODULE_PARM_DESC(cache_getent, "Path to the client cache upcall program"); | ||
| module_param_named(cache_getent_timeout, nfs_cache_getent_timeout, ulong, 0600); | ||
| MODULE_PARM_DESC(cache_getent_timeout, "Timeout (in seconds) after which " | ||
| "the cache upcall is assumed to have failed"); | ||
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| int nfs_cache_upcall(struct cache_detail *cd, char *entry_name) | ||
| { | ||
| static char *envp[] = { "HOME=/", | ||
| "TERM=linux", | ||
| "PATH=/sbin:/usr/sbin:/bin:/usr/bin", | ||
| NULL | ||
| }; | ||
| char *argv[] = { | ||
| nfs_cache_getent_prog, | ||
| cd->name, | ||
| entry_name, | ||
| NULL | ||
| }; | ||
| int ret = -EACCES; | ||
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| if (nfs_cache_getent_prog[0] == '\0') | ||
| goto out; | ||
| ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC); | ||
| /* | ||
| * Disable the upcall mechanism if we're getting an ENOENT or | ||
| * EACCES error. The admin can re-enable it on the fly by using | ||
| * sysfs to set the 'cache_getent' parameter once the problem | ||
| * has been fixed. | ||
| */ | ||
| if (ret == -ENOENT || ret == -EACCES) | ||
| nfs_cache_getent_prog[0] = '\0'; | ||
| out: | ||
| return ret > 0 ? 0 : ret; | ||
| } | ||
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| /* | ||
| * Deferred request handling | ||
| */ | ||
| void nfs_cache_defer_req_put(struct nfs_cache_defer_req *dreq) | ||
| { | ||
| if (atomic_dec_and_test(&dreq->count)) | ||
| kfree(dreq); | ||
| } | ||
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| static void nfs_dns_cache_revisit(struct cache_deferred_req *d, int toomany) | ||
| { | ||
| struct nfs_cache_defer_req *dreq; | ||
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| dreq = container_of(d, struct nfs_cache_defer_req, deferred_req); | ||
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| complete_all(&dreq->completion); | ||
| nfs_cache_defer_req_put(dreq); | ||
| } | ||
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| static struct cache_deferred_req *nfs_dns_cache_defer(struct cache_req *req) | ||
| { | ||
| struct nfs_cache_defer_req *dreq; | ||
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| dreq = container_of(req, struct nfs_cache_defer_req, req); | ||
| dreq->deferred_req.revisit = nfs_dns_cache_revisit; | ||
| atomic_inc(&dreq->count); | ||
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| return &dreq->deferred_req; | ||
| } | ||
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| struct nfs_cache_defer_req *nfs_cache_defer_req_alloc(void) | ||
| { | ||
| struct nfs_cache_defer_req *dreq; | ||
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| dreq = kzalloc(sizeof(*dreq), GFP_KERNEL); | ||
| if (dreq) { | ||
| init_completion(&dreq->completion); | ||
| atomic_set(&dreq->count, 1); | ||
| dreq->req.defer = nfs_dns_cache_defer; | ||
| } | ||
| return dreq; | ||
| } | ||
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| int nfs_cache_wait_for_upcall(struct nfs_cache_defer_req *dreq) | ||
| { | ||
| if (wait_for_completion_timeout(&dreq->completion, | ||
| nfs_cache_getent_timeout * HZ) == 0) | ||
| return -ETIMEDOUT; | ||
| return 0; | ||
| } | ||
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| int nfs_cache_register(struct cache_detail *cd) | ||
| { | ||
| struct nameidata nd; | ||
| struct vfsmount *mnt; | ||
| int ret; | ||
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| mnt = rpc_get_mount(); | ||
| if (IS_ERR(mnt)) | ||
| return PTR_ERR(mnt); | ||
| ret = vfs_path_lookup(mnt->mnt_root, mnt, "/cache", 0, &nd); | ||
| if (ret) | ||
| goto err; | ||
| ret = sunrpc_cache_register_pipefs(nd.path.dentry, | ||
| cd->name, 0600, cd); | ||
| path_put(&nd.path); | ||
| if (!ret) | ||
| return ret; | ||
| err: | ||
| rpc_put_mount(); | ||
| return ret; | ||
| } | ||
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| void nfs_cache_unregister(struct cache_detail *cd) | ||
| { | ||
| sunrpc_cache_unregister_pipefs(cd); | ||
| rpc_put_mount(); | ||
| } | ||
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