afs: Implement VL server rotation

Track VL servers as independent entities rather than lumping all their
addresses together into one set and implement server-level rotation by:

 (1) Add the concept of a VL server list, where each server has its own
     separate address list.  This code is similar to the FS server list.

 (2) Use the DNS resolver to retrieve a set of servers and their associated
     addresses, ports, preference and weight ratings.

 (3) In the case of a legacy DNS resolver or an address list given directly
     through /proc/net/afs/cells, create a list containing just a dummy
     server record and attach all the addresses to that.

 (4) Implement a simple rotation policy, for the moment ignoring the
     priorities and weights assigned to the servers.

 (5) Show the address list through /proc/net/afs/<cell>/vlservers.  This
     also displays the source and status of the data as indicated by the
     upcall.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 336 insertions, 0 deletions

diff --git a/fs/afs/vl_list.c b/fs/afs/vl_list.c
new file mode 100644
index 000000000000..c1e316ba105a
--- /dev/null
+++ b/fs/afs/vl_list.c
@@ -0,0 +1,336 @@
+/* AFS vlserver list management.
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include "internal.h"
+
+struct afs_vlserver *afs_alloc_vlserver(const char *name, size_t name_len,
+					unsigned short port)
+{
+	struct afs_vlserver *vlserver;
+
+	vlserver = kzalloc(struct_size(vlserver, name, name_len + 1),
+			   GFP_KERNEL);
+	if (vlserver) {
+		atomic_set(&vlserver->usage, 1);
+		rwlock_init(&vlserver->lock);
+		vlserver->name_len = name_len;
+		vlserver->port = port;
+		memcpy(vlserver->name, name, name_len);
+	}
+	return vlserver;
+}
+
+static void afs_vlserver_rcu(struct rcu_head *rcu)
+{
+	struct afs_vlserver *vlserver = container_of(rcu, struct afs_vlserver, rcu);
+
+	afs_put_addrlist(rcu_access_pointer(vlserver->addresses));
+	kfree_rcu(vlserver, rcu);
+}
+
+void afs_put_vlserver(struct afs_net *net, struct afs_vlserver *vlserver)
+{
+	if (vlserver) {
+		unsigned int u = atomic_dec_return(&vlserver->usage);
+		//_debug("VL PUT %p{%u}", vlserver, u);
+
+		if (u == 0)
+			call_rcu(&vlserver->rcu, afs_vlserver_rcu);
+	}
+}
+
+struct afs_vlserver_list *afs_alloc_vlserver_list(unsigned int nr_servers)
+{
+	struct afs_vlserver_list *vllist;
+
+	vllist = kzalloc(struct_size(vllist, servers, nr_servers), GFP_KERNEL);
+	if (vllist) {
+		atomic_set(&vllist->usage, 1);
+		rwlock_init(&vllist->lock);
+	}
+
+	return vllist;
+}
+
+void afs_put_vlserverlist(struct afs_net *net, struct afs_vlserver_list *vllist)
+{
+	if (vllist) {
+		unsigned int u = atomic_dec_return(&vllist->usage);
+
+		//_debug("VLLS PUT %p{%u}", vllist, u);
+		if (u == 0) {
+			int i;
+
+			for (i = 0; i < vllist->nr_servers; i++) {
+				afs_put_vlserver(net, vllist->servers[i].server);
+			}
+			kfree_rcu(vllist, rcu);
+		}
+	}
+}
+
+static u16 afs_extract_le16(const u8 **_b)
+{
+	u16 val;
+
+	val  = (u16)*(*_b)++ << 0;
+	val |= (u16)*(*_b)++ << 8;
+	return val;
+}
+
+/*
+ * Build a VL server address list from a DNS queried server list.
+ */
+static struct afs_addr_list *afs_extract_vl_addrs(const u8 **_b, const u8 *end,
+						  u8 nr_addrs, u16 port)
+{
+	struct afs_addr_list *alist;
+	const u8 *b = *_b;
+	int ret = -EINVAL;
+
+	alist = afs_alloc_addrlist(nr_addrs, VL_SERVICE, port);
+	if (!alist)
+		return ERR_PTR(-ENOMEM);
+	if (nr_addrs == 0)
+		return alist;
+
+	for (; nr_addrs > 0 && end - b >= nr_addrs; nr_addrs--) {
+		struct dns_server_list_v1_address hdr;
+		__be32 x[4];
+
+		hdr.address_type = *b++;
+
+		switch (hdr.address_type) {
+		case DNS_ADDRESS_IS_IPV4:
+			if (end - b < 4) {
+				_leave(" = -EINVAL [short inet]");
+				goto error;
+			}
+			memcpy(x, b, 4);
+			afs_merge_fs_addr4(alist, x[0], port);
+			b += 4;
+			break;
+
+		case DNS_ADDRESS_IS_IPV6:
+			if (end - b < 16) {
+				_leave(" = -EINVAL [short inet6]");
+				goto error;
+			}
+			memcpy(x, b, 16);
+			afs_merge_fs_addr6(alist, x, port);
+			b += 16;
+			break;
+
+		default:
+			_leave(" = -EADDRNOTAVAIL [unknown af %u]",
+			       hdr.address_type);
+			ret = -EADDRNOTAVAIL;
+			goto error;
+		}
+	}
+
+	/* Start with IPv6 if available. */
+	if (alist->nr_ipv4 < alist->nr_addrs)
+		alist->index = alist->nr_ipv4;
+
+	*_b = b;
+	return alist;
+
+error:
+	*_b = b;
+	afs_put_addrlist(alist);
+	return ERR_PTR(ret);
+}
+
+/*
+ * Build a VL server list from a DNS queried server list.
+ */
+struct afs_vlserver_list *afs_extract_vlserver_list(struct afs_cell *cell,
+						    const void *buffer,
+						    size_t buffer_size)
+{
+	const struct dns_server_list_v1_header *hdr = buffer;
+	struct dns_server_list_v1_server bs;
+	struct afs_vlserver_list *vllist, *previous;
+	struct afs_addr_list *addrs;
+	struct afs_vlserver *server;
+	const u8 *b = buffer, *end = buffer + buffer_size;
+	int ret = -ENOMEM, nr_servers, i, j;
+
+	_enter("");
+
+	/* Check that it's a server list, v1 */
+	if (end - b < sizeof(*hdr) ||
+	    hdr->hdr.content != DNS_PAYLOAD_IS_SERVER_LIST ||
+	    hdr->hdr.version != 1) {
+		pr_notice("kAFS: Got DNS record [%u,%u] len %zu\n",
+			  hdr->hdr.content, hdr->hdr.version, end - b);
+		ret = -EDESTADDRREQ;
+		goto dump;
+	}
+
+	nr_servers = hdr->nr_servers;
+
+	vllist = afs_alloc_vlserver_list(nr_servers);
+	if (!vllist)
+		return ERR_PTR(-ENOMEM);
+
+	vllist->source = (hdr->source < NR__dns_record_source) ?
+		hdr->source : NR__dns_record_source;
+	vllist->status = (hdr->status < NR__dns_lookup_status) ?
+		hdr->status : NR__dns_lookup_status;
+
+	read_lock(&cell->vl_servers_lock);
+	previous = afs_get_vlserverlist(
+		rcu_dereference_protected(cell->vl_servers,
+					  lockdep_is_held(&cell->vl_servers_lock)));
+	read_unlock(&cell->vl_servers_lock);
+
+	b += sizeof(*hdr);
+	while (end - b >= sizeof(bs)) {
+		bs.name_len	= afs_extract_le16(&b);
+		bs.priority	= afs_extract_le16(&b);
+		bs.weight	= afs_extract_le16(&b);
+		bs.port		= afs_extract_le16(&b);
+		bs.source	= *b++;
+		bs.status	= *b++;
+		bs.protocol	= *b++;
+		bs.nr_addrs	= *b++;
+
+		_debug("extract %u %u %u %u %u %u %*.*s",
+		       bs.name_len, bs.priority, bs.weight,
+		       bs.port, bs.protocol, bs.nr_addrs,
+		       bs.name_len, bs.name_len, b);
+
+		if (end - b < bs.name_len)
+			break;
+
+		ret = -EPROTONOSUPPORT;
+		if (bs.protocol == DNS_SERVER_PROTOCOL_UNSPECIFIED) {
+			bs.protocol = DNS_SERVER_PROTOCOL_UDP;
+		} else if (bs.protocol != DNS_SERVER_PROTOCOL_UDP) {
+			_leave(" = [proto %u]", bs.protocol);
+			goto error;
+		}
+
+		if (bs.port == 0)
+			bs.port = AFS_VL_PORT;
+		if (bs.source > NR__dns_record_source)
+			bs.source = NR__dns_record_source;
+		if (bs.status > NR__dns_lookup_status)
+			bs.status = NR__dns_lookup_status;
+
+		server = NULL;
+		if (previous) {
+			/* See if we can update an old server record */
+			for (i = 0; i < previous->nr_servers; i++) {
+				struct afs_vlserver *p = previous->servers[i].server;
+
+				if (p->name_len == bs.name_len &&
+				    p->port == bs.port &&
+				    strncasecmp(b, p->name, bs.name_len) == 0) {
+					server = afs_get_vlserver(p);
+					break;
+				}
+			}
+		}
+
+		if (!server) {
+			ret = -ENOMEM;
+			server = afs_alloc_vlserver(b, bs.name_len, bs.port);
+			if (!server)
+				goto error;
+		}
+
+		b += bs.name_len;
+
+		/* Extract the addresses - note that we can't skip this as we
+		 * have to advance the payload pointer.
+		 */
+		addrs = afs_extract_vl_addrs(&b, end, bs.nr_addrs, bs.port);
+		if (IS_ERR(addrs)) {
+			ret = PTR_ERR(addrs);
+			goto error_2;
+		}
+
+		if (vllist->nr_servers >= nr_servers) {
+			_debug("skip %u >= %u", vllist->nr_servers, nr_servers);
+			afs_put_addrlist(addrs);
+			afs_put_vlserver(cell->net, server);
+			continue;
+		}
+
+		addrs->source = bs.source;
+		addrs->status = bs.status;
+
+		if (addrs->nr_addrs == 0) {
+			afs_put_addrlist(addrs);
+			if (!rcu_access_pointer(server->addresses)) {
+				afs_put_vlserver(cell->net, server);
+				continue;
+			}
+		} else {
+			struct afs_addr_list *old = addrs;
+
+			write_lock(&server->lock);
+			rcu_swap_protected(server->addresses, old,
+					   lockdep_is_held(&server->lock));
+			write_unlock(&server->lock);
+			afs_put_addrlist(old);
+		}
+
+
+		/* TODO: Might want to check for duplicates */
+
+		/* Insertion-sort by priority and weight */
+		for (j = 0; j < vllist->nr_servers; j++) {
+			if (bs.priority < vllist->servers[j].priority)
+				break; /* Lower preferable */
+			if (bs.priority == vllist->servers[j].priority &&
+			    bs.weight > vllist->servers[j].weight)
+				break; /* Higher preferable */
+		}
+
+		if (j < vllist->nr_servers) {
+			memmove(vllist->servers + j + 1,
+				vllist->servers + j,
+				(vllist->nr_servers - j) * sizeof(struct afs_vlserver_entry));
+		}
+
+		vllist->servers[j].priority = bs.priority;
+		vllist->servers[j].weight = bs.weight;
+		vllist->servers[j].server = server;
+		vllist->nr_servers++;
+	}
+
+	if (b != end) {
+		_debug("parse error %zd", b - end);
+		goto error;
+	}
+
+	afs_put_vlserverlist(cell->net, previous);
+	_leave(" = ok [%u]", vllist->nr_servers);
+	return vllist;
+
+error_2:
+	afs_put_vlserver(cell->net, server);
+error:
+	afs_put_vlserverlist(cell->net, vllist);
+	afs_put_vlserverlist(cell->net, previous);
+dump:
+	if (ret != -ENOMEM) {
+		printk(KERN_DEBUG "DNS: at %zu\n", (const void *)b - buffer);
+		print_hex_dump_bytes("DNS: ", DUMP_PREFIX_NONE, buffer, buffer_size);
+	}
+	return ERR_PTR(ret);
+}