NFS: Add a dns resolver for use with NFSv4 referrals and migration

The NFSv4 and NFSv4.1 protocols both allow for the redirection of a client
from one server to another in order to support filesystem migration and
replication. For full protocol support, we need to add the ability to
convert a DNS host name into an IP address that we can feed to the RPC
client.

We'll reuse the sunrpc cache, now that it has been converted to work with
rpc_pipefs.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 140 insertions, 0 deletions

diff --git a/fs/nfs/cache_lib.c b/fs/nfs/cache_lib.c
new file mode 100644
index 000000000000..b4ffd0146ea6
--- /dev/null
+++ b/fs/nfs/cache_lib.c
@@ -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>
+
+#include "cache_lib.h"
+
+#define NFS_CACHE_UPCALL_PATHLEN 256
+#define NFS_CACHE_UPCALL_TIMEOUT 15
+
+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;
+
+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");
+
+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;
+
+        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;
+}
+
+/*
+ * Deferred request handling
+ */
+void nfs_cache_defer_req_put(struct nfs_cache_defer_req *dreq)
+{
+        if (atomic_dec_and_test(&dreq->count))
+                kfree(dreq);
+}
+
+static void nfs_dns_cache_revisit(struct cache_deferred_req *d, int toomany)
+{
+        struct nfs_cache_defer_req *dreq;
+
+        dreq = container_of(d, struct nfs_cache_defer_req, deferred_req);
+
+        complete_all(&dreq->completion);
+        nfs_cache_defer_req_put(dreq);
+}
+
+static struct cache_deferred_req *nfs_dns_cache_defer(struct cache_req *req)
+{
+        struct nfs_cache_defer_req *dreq;
+
+        dreq = container_of(req, struct nfs_cache_defer_req, req);
+        dreq->deferred_req.revisit = nfs_dns_cache_revisit;
+        atomic_inc(&dreq->count);
+
+        return &dreq->deferred_req;
+}
+
+struct nfs_cache_defer_req *nfs_cache_defer_req_alloc(void)
+{
+        struct nfs_cache_defer_req *dreq;
+
+        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;
+}
+
+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;
+}
+
+int nfs_cache_register(struct cache_detail *cd)
+{
+        struct nameidata nd;
+        struct vfsmount *mnt;
+        int ret;
+
+        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;
+}
+
+void nfs_cache_unregister(struct cache_detail *cd)
+{
+        sunrpc_cache_unregister_pipefs(cd);
+        rpc_put_mount();
+}
+