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, 335 insertions, 0 deletions

diff --git a/fs/nfs/dns_resolve.c b/fs/nfs/dns_resolve.c
new file mode 100644
index 000000000000..f4d54ba97cc6
--- /dev/null
+++ b/fs/nfs/dns_resolve.c
@@ -0,0 +1,335 @@
+/*
+ * linux/fs/nfs/dns_resolve.c
+ *
+ * Copyright (c) 2009 Trond Myklebust <Trond.Myklebust@netapp.com>
+ *
+ * Resolves DNS hostnames into valid ip addresses
+ */
+
+#include <linux/hash.h>
+#include <linux/string.h>
+#include <linux/kmod.h>
+#include <linux/module.h>
+#include <linux/socket.h>
+#include <linux/seq_file.h>
+#include <linux/inet.h>
+#include <linux/sunrpc/clnt.h>
+#include <linux/sunrpc/cache.h>
+#include <linux/sunrpc/svcauth.h>
+
+#include "dns_resolve.h"
+#include "cache_lib.h"
+
+#define NFS_DNS_HASHBITS 4
+#define NFS_DNS_HASHTBL_SIZE (1 << NFS_DNS_HASHBITS)
+
+static struct cache_head *nfs_dns_table[NFS_DNS_HASHTBL_SIZE];
+
+struct nfs_dns_ent {
+        struct cache_head h;
+
+        char *hostname;
+        size_t namelen;
+
+        struct sockaddr_storage addr;
+        size_t addrlen;
+};
+
+
+static void nfs_dns_ent_init(struct cache_head *cnew,
+                struct cache_head *ckey)
+{
+        struct nfs_dns_ent *new;
+        struct nfs_dns_ent *key;
+
+        new = container_of(cnew, struct nfs_dns_ent, h);
+        key = container_of(ckey, struct nfs_dns_ent, h);
+
+        kfree(new->hostname);
+        new->hostname = kstrndup(key->hostname, key->namelen, GFP_KERNEL);
+        if (new->hostname) {
+                new->namelen = key->namelen;
+                memcpy(&new->addr, &key->addr, key->addrlen);
+                new->addrlen = key->addrlen;
+        } else {
+                new->namelen = 0;
+                new->addrlen = 0;
+        }
+}
+
+static void nfs_dns_ent_put(struct kref *ref)
+{
+        struct nfs_dns_ent *item;
+
+        item = container_of(ref, struct nfs_dns_ent, h.ref);
+        kfree(item->hostname);
+        kfree(item);
+}
+
+static struct cache_head *nfs_dns_ent_alloc(void)
+{
+        struct nfs_dns_ent *item = kmalloc(sizeof(*item), GFP_KERNEL);
+
+        if (item != NULL) {
+                item->hostname = NULL;
+                item->namelen = 0;
+                item->addrlen = 0;
+                return &item->h;
+        }
+        return NULL;
+};
+
+static unsigned int nfs_dns_hash(const struct nfs_dns_ent *key)
+{
+        return hash_str(key->hostname, NFS_DNS_HASHBITS);
+}
+
+static void nfs_dns_request(struct cache_detail *cd,
+                struct cache_head *ch,
+                char **bpp, int *blen)
+{
+        struct nfs_dns_ent *key = container_of(ch, struct nfs_dns_ent, h);
+
+        qword_add(bpp, blen, key->hostname);
+        (*bpp)[-1] = '\n';
+}
+
+static int nfs_dns_upcall(struct cache_detail *cd,
+                struct cache_head *ch)
+{
+        struct nfs_dns_ent *key = container_of(ch, struct nfs_dns_ent, h);
+        int ret;
+
+        ret = nfs_cache_upcall(cd, key->hostname);
+        if (ret)
+                ret = sunrpc_cache_pipe_upcall(cd, ch, nfs_dns_request);
+        return ret;
+}
+
+static int nfs_dns_match(struct cache_head *ca,
+                struct cache_head *cb)
+{
+        struct nfs_dns_ent *a;
+        struct nfs_dns_ent *b;
+
+        a = container_of(ca, struct nfs_dns_ent, h);
+        b = container_of(cb, struct nfs_dns_ent, h);
+
+        if (a->namelen == 0 || a->namelen != b->namelen)
+                return 0;
+        return memcmp(a->hostname, b->hostname, a->namelen) == 0;
+}
+
+static int nfs_dns_show(struct seq_file *m, struct cache_detail *cd,
+                struct cache_head *h)
+{
+        struct nfs_dns_ent *item;
+        long ttl;
+
+        if (h == NULL) {
+                seq_puts(m, "# ip address      hostname        ttl\n");
+                return 0;
+        }
+        item = container_of(h, struct nfs_dns_ent, h);
+        ttl = (long)item->h.expiry_time - (long)get_seconds();
+        if (ttl < 0)
+                ttl = 0;
+
+        if (!test_bit(CACHE_NEGATIVE, &h->flags)) {
+                char buf[INET6_ADDRSTRLEN+IPV6_SCOPE_ID_LEN+1];
+
+                rpc_ntop((struct sockaddr *)&item->addr, buf, sizeof(buf));
+                seq_printf(m, "%15s ", buf);
+        } else
+                seq_puts(m, "<none>          ");
+        seq_printf(m, "%15s %ld\n", item->hostname, ttl);
+        return 0;
+}
+
+struct nfs_dns_ent *nfs_dns_lookup(struct cache_detail *cd,
+                struct nfs_dns_ent *key)
+{
+        struct cache_head *ch;
+
+        ch = sunrpc_cache_lookup(cd,
+                        &key->h,
+                        nfs_dns_hash(key));
+        if (!ch)
+                return NULL;
+        return container_of(ch, struct nfs_dns_ent, h);
+}
+
+struct nfs_dns_ent *nfs_dns_update(struct cache_detail *cd,
+                struct nfs_dns_ent *new,
+                struct nfs_dns_ent *key)
+{
+        struct cache_head *ch;
+
+        ch = sunrpc_cache_update(cd,
+                        &new->h, &key->h,
+                        nfs_dns_hash(key));
+        if (!ch)
+                return NULL;
+        return container_of(ch, struct nfs_dns_ent, h);
+}
+
+static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen)
+{
+        char buf1[NFS_DNS_HOSTNAME_MAXLEN+1];
+        struct nfs_dns_ent key, *item;
+        unsigned long ttl;
+        ssize_t len;
+        int ret = -EINVAL;
+
+        if (buf[buflen-1] != '\n')
+                goto out;
+        buf[buflen-1] = '\0';
+
+        len = qword_get(&buf, buf1, sizeof(buf1));
+        if (len <= 0)
+                goto out;
+        key.addrlen = rpc_pton(buf1, len,
+                        (struct sockaddr *)&key.addr,
+                        sizeof(key.addr));
+
+        len = qword_get(&buf, buf1, sizeof(buf1));
+        if (len <= 0)
+                goto out;
+
+        key.hostname = buf1;
+        key.namelen = len;
+        memset(&key.h, 0, sizeof(key.h));
+
+        ttl = get_expiry(&buf);
+        if (ttl == 0)
+                goto out;
+        key.h.expiry_time = ttl + get_seconds();
+
+        ret = -ENOMEM;
+        item = nfs_dns_lookup(cd, &key);
+        if (item == NULL)
+                goto out;
+
+        if (key.addrlen == 0)
+                set_bit(CACHE_NEGATIVE, &key.h.flags);
+
+        item = nfs_dns_update(cd, &key, item);
+        if (item == NULL)
+                goto out;
+
+        ret = 0;
+        cache_put(&item->h, cd);
+out:
+        return ret;
+}
+
+static struct cache_detail nfs_dns_resolve = {
+        .owner = THIS_MODULE,
+        .hash_size = NFS_DNS_HASHTBL_SIZE,
+        .hash_table = nfs_dns_table,
+        .name = "dns_resolve",
+        .cache_put = nfs_dns_ent_put,
+        .cache_upcall = nfs_dns_upcall,
+        .cache_parse = nfs_dns_parse,
+        .cache_show = nfs_dns_show,
+        .match = nfs_dns_match,
+        .init = nfs_dns_ent_init,
+        .update = nfs_dns_ent_init,
+        .alloc = nfs_dns_ent_alloc,
+};
+
+static int do_cache_lookup(struct cache_detail *cd,
+                struct nfs_dns_ent *key,
+                struct nfs_dns_ent **item,
+                struct nfs_cache_defer_req *dreq)
+{
+        int ret = -ENOMEM;
+
+        *item = nfs_dns_lookup(cd, key);
+        if (*item) {
+                ret = cache_check(cd, &(*item)->h, &dreq->req);
+                if (ret)
+                        *item = NULL;
+        }
+        return ret;
+}
+
+static int do_cache_lookup_nowait(struct cache_detail *cd,
+                struct nfs_dns_ent *key,
+                struct nfs_dns_ent **item)
+{
+        int ret = -ENOMEM;
+
+        *item = nfs_dns_lookup(cd, key);
+        if (!*item)
+                goto out_err;
+        ret = -ETIMEDOUT;
+        if (!test_bit(CACHE_VALID, &(*item)->h.flags)
+                        || (*item)->h.expiry_time < get_seconds()
+                        || cd->flush_time > (*item)->h.last_refresh)
+                goto out_put;
+        ret = -ENOENT;
+        if (test_bit(CACHE_NEGATIVE, &(*item)->h.flags))
+                goto out_put;
+        return 0;
+out_put:
+        cache_put(&(*item)->h, cd);
+out_err:
+        *item = NULL;
+        return ret;
+}
+
+static int do_cache_lookup_wait(struct cache_detail *cd,
+                struct nfs_dns_ent *key,
+                struct nfs_dns_ent **item)
+{
+        struct nfs_cache_defer_req *dreq;
+        int ret = -ENOMEM;
+
+        dreq = nfs_cache_defer_req_alloc();
+        if (!dreq)
+                goto out;
+        ret = do_cache_lookup(cd, key, item, dreq);
+        if (ret == -EAGAIN) {
+                ret = nfs_cache_wait_for_upcall(dreq);
+                if (!ret)
+                        ret = do_cache_lookup_nowait(cd, key, item);
+        }
+        nfs_cache_defer_req_put(dreq);
+out:
+        return ret;
+}
+
+ssize_t nfs_dns_resolve_name(char *name, size_t namelen,
+                struct sockaddr *sa, size_t salen)
+{
+        struct nfs_dns_ent key = {
+                .hostname = name,
+                .namelen = namelen,
+        };
+        struct nfs_dns_ent *item = NULL;
+        ssize_t ret;
+
+        ret = do_cache_lookup_wait(&nfs_dns_resolve, &key, &item);
+        if (ret == 0) {
+                if (salen >= item->addrlen) {
+                        memcpy(sa, &item->addr, item->addrlen);
+                        ret = item->addrlen;
+                } else
+                        ret = -EOVERFLOW;
+                cache_put(&item->h, &nfs_dns_resolve);
+        } else if (ret == -ENOENT)
+                ret = -ESRCH;
+        return ret;
+}
+
+int nfs_dns_resolver_init(void)
+{
+        return nfs_cache_register(&nfs_dns_resolve);
+}
+
+void nfs_dns_resolver_destroy(void)
+{
+        nfs_cache_unregister(&nfs_dns_resolve);
+}
+