[linux.git] / fs / afs / addr_list.c

/* Server address list management
 *
 * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/slab.h>
#include <linux/ctype.h>
#include <linux/dns_resolver.h>
#include <linux/inet.h>
#include <keys/rxrpc-type.h>
#include "internal.h"
#include "afs_fs.h"

//#define AFS_MAX_ADDRESSES
//	((unsigned int)((PAGE_SIZE - sizeof(struct afs_addr_list)) /
//			sizeof(struct sockaddr_rxrpc)))
#define AFS_MAX_ADDRESSES ((unsigned int)(sizeof(unsigned long) * 8))

/*
 * Release an address list.
 */
void afs_put_addrlist(struct afs_addr_list *alist)
{
	if (alist && refcount_dec_and_test(&alist->usage))
		call_rcu(&alist->rcu, (rcu_callback_t)kfree);
}

/*
 * Allocate an address list.
 */
struct afs_addr_list *afs_alloc_addrlist(unsigned int nr,
					 unsigned short service,
					 unsigned short port)
{
	struct afs_addr_list *alist;
	unsigned int i;

	_enter("%u,%u,%u", nr, service, port);

	alist = kzalloc(struct_size(alist, addrs, nr), GFP_KERNEL);
	if (!alist)
		return NULL;

	refcount_set(&alist->usage, 1);

	for (i = 0; i < nr; i++) {
		struct sockaddr_rxrpc *srx = &alist->addrs[i];
		srx->srx_family			= AF_RXRPC;
		srx->srx_service		= service;
		srx->transport_type		= SOCK_DGRAM;
		srx->transport_len		= sizeof(srx->transport.sin6);
		srx->transport.sin6.sin6_family	= AF_INET6;
		srx->transport.sin6.sin6_port	= htons(port);
	}

	return alist;
}

/*
 * Parse a text string consisting of delimited addresses.
 */
struct afs_addr_list *afs_parse_text_addrs(const char *text, size_t len,
					   char delim,
					   unsigned short service,
					   unsigned short port)
{
	struct afs_addr_list *alist;
	const char *p, *end = text + len;
	unsigned int nr = 0;

	_enter("%*.*s,%c", (int)len, (int)len, text, delim);

	if (!len)
		return ERR_PTR(-EDESTADDRREQ);

	if (delim == ':' && (memchr(text, ',', len) || !memchr(text, '.', len)))
		delim = ',';

	/* Count the addresses */
	p = text;
	do {
		if (!*p)
			return ERR_PTR(-EINVAL);
		if (*p == delim)
			continue;
		nr++;
		if (*p == '[') {
			p++;
			if (p == end)
				return ERR_PTR(-EINVAL);
			p = memchr(p, ']', end - p);
			if (!p)
				return ERR_PTR(-EINVAL);
			p++;
			if (p >= end)
				break;
		}

		p = memchr(p, delim, end - p);
		if (!p)
			break;
		p++;
	} while (p < end);

	_debug("%u/%u addresses", nr, AFS_MAX_ADDRESSES);
	if (nr > AFS_MAX_ADDRESSES)
		nr = AFS_MAX_ADDRESSES;

	alist = afs_alloc_addrlist(nr, service, port);
	if (!alist)
		return ERR_PTR(-ENOMEM);

	/* Extract the addresses */
	p = text;
	do {
		struct sockaddr_rxrpc *srx = &alist->addrs[alist->nr_addrs];
		const char *q, *stop;

		if (*p == delim) {
			p++;
			continue;
		}

		if (*p == '[') {
			p++;
			q = memchr(p, ']', end - p);
		} else {
			for (q = p; q < end; q++)
				if (*q == '+' || *q == delim)
					break;
		}

		if (in4_pton(p, q - p,
			     (u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
			     -1, &stop)) {
			srx->transport.sin6.sin6_addr.s6_addr32[0] = 0;
			srx->transport.sin6.sin6_addr.s6_addr32[1] = 0;
			srx->transport.sin6.sin6_addr.s6_addr32[2] = htonl(0xffff);
		} else if (in6_pton(p, q - p,
				    srx->transport.sin6.sin6_addr.s6_addr,
				    -1, &stop)) {
			/* Nothing to do */
		} else {
			goto bad_address;
		}

		if (stop != q)
			goto bad_address;

		p = q;
		if (q < end && *q == ']')
			p++;

		if (p < end) {
			if (*p == '+') {
				/* Port number specification "+1234" */
				unsigned int xport = 0;
				p++;
				if (p >= end || !isdigit(*p))
					goto bad_address;
				do {
					xport *= 10;
					xport += *p - '0';
					if (xport > 65535)
						goto bad_address;
					p++;
				} while (p < end && isdigit(*p));
				srx->transport.sin6.sin6_port = htons(xport);
			} else if (*p == delim) {
				p++;
			} else {
				goto bad_address;
			}
		}

		alist->nr_addrs++;
	} while (p < end && alist->nr_addrs < AFS_MAX_ADDRESSES);

	_leave(" = [nr %u]", alist->nr_addrs);
	return alist;

bad_address:
	kfree(alist);
	return ERR_PTR(-EINVAL);
}

/*
 * Compare old and new address lists to see if there's been any change.
 * - How to do this in better than O(Nlog(N)) time?
 *   - We don't really want to sort the address list, but would rather take the
 *     list as we got it so as not to undo record rotation by the DNS server.
 */
#if 0
static int afs_cmp_addr_list(const struct afs_addr_list *a1,
			     const struct afs_addr_list *a2)
{
}
#endif

/*
 * Perform a DNS query for VL servers and build a up an address list.
 */
struct afs_addr_list *afs_dns_query(struct afs_cell *cell, time64_t *_expiry)
{
	struct afs_addr_list *alist;
	char *vllist = NULL;
	int ret;

	_enter("%s", cell->name);

	ret = dns_query("afsdb", cell->name, cell->name_len,
			"", &vllist, _expiry);
	if (ret < 0)
		return ERR_PTR(ret);

	alist = afs_parse_text_addrs(vllist, strlen(vllist), ',',
				     VL_SERVICE, AFS_VL_PORT);
	if (IS_ERR(alist)) {
		kfree(vllist);
		if (alist != ERR_PTR(-ENOMEM))
			pr_err("Failed to parse DNS data\n");
		return alist;
	}

	kfree(vllist);
	return alist;
}

/*
 * Merge an IPv4 entry into a fileserver address list.
 */
void afs_merge_fs_addr4(struct afs_addr_list *alist, __be32 xdr, u16 port)
{
	struct sockaddr_in6 *a;
	__be16 xport = htons(port);
	int i;

	for (i = 0; i < alist->nr_ipv4; i++) {
		a = &alist->addrs[i].transport.sin6;
		if (xdr == a->sin6_addr.s6_addr32[3] &&
		    xport == a->sin6_port)
			return;
		if (xdr == a->sin6_addr.s6_addr32[3] &&
		    (u16 __force)xport < (u16 __force)a->sin6_port)
			break;
		if ((u32 __force)xdr < (u32 __force)a->sin6_addr.s6_addr32[3])
			break;
	}

	if (i < alist->nr_addrs)
		memmove(alist->addrs + i + 1,
			alist->addrs + i,
			sizeof(alist->addrs[0]) * (alist->nr_addrs - i));

	a = &alist->addrs[i].transport.sin6;
	a->sin6_port		  = xport;
	a->sin6_addr.s6_addr32[0] = 0;
	a->sin6_addr.s6_addr32[1] = 0;
	a->sin6_addr.s6_addr32[2] = htonl(0xffff);
	a->sin6_addr.s6_addr32[3] = xdr;
	alist->nr_ipv4++;
	alist->nr_addrs++;
}

/*
 * Merge an IPv6 entry into a fileserver address list.
 */
void afs_merge_fs_addr6(struct afs_addr_list *alist, __be32 *xdr, u16 port)
{
	struct sockaddr_in6 *a;
	__be16 xport = htons(port);
	int i, diff;

	for (i = alist->nr_ipv4; i < alist->nr_addrs; i++) {
		a = &alist->addrs[i].transport.sin6;
		diff = memcmp(xdr, &a->sin6_addr, 16);
		if (diff == 0 &&
		    xport == a->sin6_port)
			return;
		if (diff == 0 &&
		    (u16 __force)xport < (u16 __force)a->sin6_port)
			break;
		if (diff < 0)
			break;
	}

	if (i < alist->nr_addrs)
		memmove(alist->addrs + i + 1,
			alist->addrs + i,
			sizeof(alist->addrs[0]) * (alist->nr_addrs - i));

	a = &alist->addrs[i].transport.sin6;
	a->sin6_port		  = xport;
	a->sin6_addr.s6_addr32[0] = xdr[0];
	a->sin6_addr.s6_addr32[1] = xdr[1];
	a->sin6_addr.s6_addr32[2] = xdr[2];
	a->sin6_addr.s6_addr32[3] = xdr[3];
	alist->nr_addrs++;
}

/*
 * Get an address to try.
 */
bool afs_iterate_addresses(struct afs_addr_cursor *ac)
{
	_enter("%hu+%hd", ac->start, (short)ac->index);

	if (!ac->alist)
		return false;

	if (ac->begun) {
		ac->index++;
		if (ac->index == ac->alist->nr_addrs)
			ac->index = 0;

		if (ac->index == ac->start) {
			ac->error = -EDESTADDRREQ;
			return false;
		}
	}

	ac->begun = true;
	ac->responded = false;
	ac->addr = &ac->alist->addrs[ac->index];
	return true;
}

/*
 * Release an address list cursor.
 */
int afs_end_cursor(struct afs_addr_cursor *ac)
{
	struct afs_addr_list *alist;

	alist = ac->alist;
	if (alist) {
		if (ac->responded && ac->index != ac->start)
			WRITE_ONCE(alist->index, ac->index);
		afs_put_addrlist(alist);
	}

	ac->addr = NULL;
	ac->alist = NULL;
	ac->begun = false;
	return ac->error;
}

/*
 * Set the address cursor for iterating over VL servers.
 */
int afs_set_vl_cursor(struct afs_addr_cursor *ac, struct afs_cell *cell)
{
	struct afs_addr_list *alist;
	int ret;

	if (!rcu_access_pointer(cell->vl_addrs)) {
		ret = wait_on_bit(&cell->flags, AFS_CELL_FL_NO_LOOKUP_YET,
				  TASK_INTERRUPTIBLE);
		if (ret < 0)
			return ret;

		if (!rcu_access_pointer(cell->vl_addrs) &&
		    ktime_get_real_seconds() < cell->dns_expiry)
			return cell->error;
	}

	read_lock(&cell->vl_addrs_lock);
	alist = rcu_dereference_protected(cell->vl_addrs,
					  lockdep_is_held(&cell->vl_addrs_lock));
	if (alist->nr_addrs > 0)
		afs_get_addrlist(alist);
	else
		alist = NULL;
	read_unlock(&cell->vl_addrs_lock);

	if (!alist)
		return -EDESTADDRREQ;

	ac->alist = alist;
	ac->addr = NULL;
	ac->start = READ_ONCE(alist->index);
	ac->index = ac->start;
	ac->error = 0;
	ac->begun = false;
	return 0;
}
Commit	Line	Data
8b2a464c DH	1	/* Server address list management
	2	*
	3	* Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
	4	* Written by David Howells ([email protected])
	5	*
	6	* This program is free software; you can redistribute it and/or
	7	* modify it under the terms of the GNU General Public Licence
	8	* as published by the Free Software Foundation; either version
	9	* 2 of the Licence, or (at your option) any later version.
	10	*/
	11
	12	#include <linux/slab.h>
	13	#include <linux/ctype.h>
	14	#include <linux/dns_resolver.h>
	15	#include <linux/inet.h>
	16	#include <keys/rxrpc-type.h>
	17	#include "internal.h"
	18	#include "afs_fs.h"
	19
bf99a53c DH	20	//#define AFS_MAX_ADDRESSES
	21	// ((unsigned int)((PAGE_SIZE - sizeof(struct afs_addr_list)) /
	22	// sizeof(struct sockaddr_rxrpc)))
	23	#define AFS_MAX_ADDRESSES ((unsigned int)(sizeof(unsigned long) * 8))
8b2a464c DH	24
	25	/*
	26	* Release an address list.
	27	*/
	28	void afs_put_addrlist(struct afs_addr_list *alist)
	29	{
	30	if (alist && refcount_dec_and_test(&alist->usage))
	31	call_rcu(&alist->rcu, (rcu_callback_t)kfree);
	32	}
	33
	34	/*
	35	* Allocate an address list.
	36	*/
	37	struct afs_addr_list *afs_alloc_addrlist(unsigned int nr,
	38	unsigned short service,
	39	unsigned short port)
	40	{
	41	struct afs_addr_list *alist;
	42	unsigned int i;
	43
	44	_enter("%u,%u,%u", nr, service, port);
	45
acafe7e3	46	alist = kzalloc(struct_size(alist, addrs, nr), GFP_KERNEL);
8b2a464c DH	47	if (!alist)
	48	return NULL;
	49
	50	refcount_set(&alist->usage, 1);
	51
	52	for (i = 0; i < nr; i++) {
	53	struct sockaddr_rxrpc *srx = &alist->addrs[i];
	54	srx->srx_family = AF_RXRPC;
	55	srx->srx_service = service;
	56	srx->transport_type = SOCK_DGRAM;
	57	srx->transport_len = sizeof(srx->transport.sin6);
	58	srx->transport.sin6.sin6_family = AF_INET6;
	59	srx->transport.sin6.sin6_port = htons(port);
	60	}
	61
	62	return alist;
	63	}
	64
	65	/*
	66	* Parse a text string consisting of delimited addresses.
	67	*/
	68	struct afs_addr_list afs_parse_text_addrs(const char text, size_t len,
	69	char delim,
	70	unsigned short service,
	71	unsigned short port)
	72	{
	73	struct afs_addr_list *alist;
	74	const char p, end = text + len;
	75	unsigned int nr = 0;
	76
	77	_enter("%.s,%c", (int)len, (int)len, text, delim);
	78
	79	if (!len)
	80	return ERR_PTR(-EDESTADDRREQ);
	81
	82	if (delim == ':' && (memchr(text, ',', len) \|\| !memchr(text, '.', len)))
	83	delim = ',';
	84
	85	/* Count the addresses */
	86	p = text;
	87	do {
	88	if (!*p)
	89	return ERR_PTR(-EINVAL);
	90	if (*p == delim)
	91	continue;
	92	nr++;
	93	if (*p == '[') {
	94	p++;
	95	if (p == end)
	96	return ERR_PTR(-EINVAL);
	97	p = memchr(p, ']', end - p);
	98	if (!p)
	99	return ERR_PTR(-EINVAL);
	100	p++;
	101	if (p >= end)
	102	break;
	103	}
	104
	105	p = memchr(p, delim, end - p);
	106	if (!p)
	107	break;
	108	p++;
	109	} while (p < end);
	110
111	_debug("%u/%u addresses", nr, AFS_MAX_ADDRESSES);
112	if (nr > AFS_MAX_ADDRESSES)
113	nr = AFS_MAX_ADDRESSES;
114
115	alist = afs_alloc_addrlist(nr, service, port);
116	if (!alist)
117	return ERR_PTR(-ENOMEM);
118
119	/* Extract the addresses */
120	p = text;
121	do {
122	struct sockaddr_rxrpc *srx = &alist->addrs[alist->nr_addrs];
01fd79e6	123	const char q, stop;
8b2a464c DH	124
	125	if (*p == delim) {
	126	p++;
	127	continue;
	128	}
	129
	130	if (*p == '[') {
	131	p++;
01fd79e6 DH	132	q = memchr(p, ']', end - p);
	133	} else {
	134	for (q = p; q < end; q++)
	135	if (q == '+' \|\| q == delim)
	136	break;
8b2a464c DH	137	}
8b2a464c DH	138
01fd79e6	139	if (in4_pton(p, q - p,
8b2a464c	140	(u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
01fd79e6	141	-1, &stop)) {
8b2a464c DH	142	srx->transport.sin6.sin6_addr.s6_addr32[0] = 0;
	143	srx->transport.sin6.sin6_addr.s6_addr32[1] = 0;
	144	srx->transport.sin6.sin6_addr.s6_addr32[2] = htonl(0xffff);
01fd79e6	145	} else if (in6_pton(p, q - p,
8b2a464c	146	srx->transport.sin6.sin6_addr.s6_addr,
01fd79e6	147	-1, &stop)) {
8b2a464c DH	148	/* Nothing to do */
	149	} else {
	150	goto bad_address;
	151	}
	152
01fd79e6 DH	153	if (stop != q)
	154	goto bad_address;
	155
	156	p = q;
	157	if (q < end && *q == ']')
8b2a464c	158	p++;
8b2a464c DH	159
	160	if (p < end) {
	161	if (*p == '+') {
	162	/* Port number specification "+1234" */
	163	unsigned int xport = 0;
	164	p++;
	165	if (p >= end \|\| !isdigit(*p))
	166	goto bad_address;
	167	do {
	168	xport *= 10;
	169	xport += *p - '0';
	170	if (xport > 65535)
	171	goto bad_address;
	172	p++;
	173	} while (p < end && isdigit(*p));
	174	srx->transport.sin6.sin6_port = htons(xport);
	175	} else if (*p == delim) {
	176	p++;
	177	} else {
	178	goto bad_address;
	179	}
	180	}
	181
	182	alist->nr_addrs++;
	183	} while (p < end && alist->nr_addrs < AFS_MAX_ADDRESSES);
	184
	185	_leave(" = [nr %u]", alist->nr_addrs);
	186	return alist;
	187
	188	bad_address:
	189	kfree(alist);
	190	return ERR_PTR(-EINVAL);
	191	}
	192
	193	/*
	194	* Compare old and new address lists to see if there's been any change.
	195	* - How to do this in better than O(Nlog(N)) time?
	196	* - We don't really want to sort the address list, but would rather take the
	197	* list as we got it so as not to undo record rotation by the DNS server.
	198	*/
	199	#if 0
	200	static int afs_cmp_addr_list(const struct afs_addr_list *a1,
	201	const struct afs_addr_list *a2)
	202	{
	203	}
	204	#endif
	205
	206	/*
	207	* Perform a DNS query for VL servers and build a up an address list.
	208	*/
	209	struct afs_addr_list afs_dns_query(struct afs_cell cell, time64_t *_expiry)
	210	{
	211	struct afs_addr_list *alist;
	212	char *vllist = NULL;
	213	int ret;
	214
	215	_enter("%s", cell->name);
	216
	217	ret = dns_query("afsdb", cell->name, cell->name_len,
c88d5a7f	218	"", &vllist, _expiry);
8b2a464c DH	219	if (ret < 0)
	220	return ERR_PTR(ret);
	221
	222	alist = afs_parse_text_addrs(vllist, strlen(vllist), ',',
	223	VL_SERVICE, AFS_VL_PORT);
	224	if (IS_ERR(alist)) {
	225	kfree(vllist);
	226	if (alist != ERR_PTR(-ENOMEM))
	227	pr_err("Failed to parse DNS data\n");
	228	return alist;
	229	}
	230
	231	kfree(vllist);
	232	return alist;
	233	}
	234
d2ddc776 DH	235	/*
	236	* Merge an IPv4 entry into a fileserver address list.
	237	*/
bf99a53c	238	void afs_merge_fs_addr4(struct afs_addr_list *alist, __be32 xdr, u16 port)
d2ddc776 DH	239	{
d2ddc776 DH	240	struct sockaddr_in6 *a;
bf99a53c	241	__be16 xport = htons(port);
d2ddc776 DH	242	int i;
	243
	244	for (i = 0; i < alist->nr_ipv4; i++) {
	245	a = &alist->addrs[i].transport.sin6;
bf99a53c DH	246	if (xdr == a->sin6_addr.s6_addr32[3] &&
bf99a53c DH	247	xport == a->sin6_port)
d2ddc776	248	return;
bf99a53c	249	if (xdr == a->sin6_addr.s6_addr32[3] &&
fe342cf7	250	(u16 __force)xport < (u16 __force)a->sin6_port)
bf99a53c	251	break;
fe342cf7	252	if ((u32 __force)xdr < (u32 __force)a->sin6_addr.s6_addr32[3])
d2ddc776 DH	253	break;
	254	}
	255
	256	if (i < alist->nr_addrs)
	257	memmove(alist->addrs + i + 1,
	258	alist->addrs + i,
	259	sizeof(alist->addrs[0]) * (alist->nr_addrs - i));
	260
	261	a = &alist->addrs[i].transport.sin6;
bf99a53c	262	a->sin6_port = xport;
d2ddc776 DH	263	a->sin6_addr.s6_addr32[0] = 0;
	264	a->sin6_addr.s6_addr32[1] = 0;
	265	a->sin6_addr.s6_addr32[2] = htonl(0xffff);
	266	a->sin6_addr.s6_addr32[3] = xdr;
	267	alist->nr_ipv4++;
	268	alist->nr_addrs++;
	269	}
	270
bf99a53c DH	271	/*
	272	* Merge an IPv6 entry into a fileserver address list.
	273	*/
	274	void afs_merge_fs_addr6(struct afs_addr_list alist, __be32 xdr, u16 port)
	275	{
	276	struct sockaddr_in6 *a;
	277	__be16 xport = htons(port);
	278	int i, diff;
	279
	280	for (i = alist->nr_ipv4; i < alist->nr_addrs; i++) {
	281	a = &alist->addrs[i].transport.sin6;
	282	diff = memcmp(xdr, &a->sin6_addr, 16);
	283	if (diff == 0 &&
	284	xport == a->sin6_port)
	285	return;
	286	if (diff == 0 &&
fe342cf7	287	(u16 __force)xport < (u16 __force)a->sin6_port)
bf99a53c DH	288	break;
	289	if (diff < 0)
	290	break;
	291	}
	292
	293	if (i < alist->nr_addrs)
	294	memmove(alist->addrs + i + 1,
	295	alist->addrs + i,
	296	sizeof(alist->addrs[0]) * (alist->nr_addrs - i));
	297
	298	a = &alist->addrs[i].transport.sin6;
	299	a->sin6_port = xport;
	300	a->sin6_addr.s6_addr32[0] = xdr[0];
	301	a->sin6_addr.s6_addr32[1] = xdr[1];
	302	a->sin6_addr.s6_addr32[2] = xdr[2];
	303	a->sin6_addr.s6_addr32[3] = xdr[3];
	304	alist->nr_addrs++;
	305	}
	306
8b2a464c DH	307	/*
	308	* Get an address to try.
	309	*/
	310	bool afs_iterate_addresses(struct afs_addr_cursor *ac)
	311	{
	312	_enter("%hu+%hd", ac->start, (short)ac->index);
	313
	314	if (!ac->alist)
	315	return false;
	316
	317	if (ac->begun) {
	318	ac->index++;
	319	if (ac->index == ac->alist->nr_addrs)
	320	ac->index = 0;
	321
	322	if (ac->index == ac->start) {
	323	ac->error = -EDESTADDRREQ;
	324	return false;
	325	}
	326	}
	327
	328	ac->begun = true;
	329	ac->responded = false;
	330	ac->addr = &ac->alist->addrs[ac->index];
	331	return true;
	332	}
	333
	334	/*
	335	* Release an address list cursor.
	336	*/
	337	int afs_end_cursor(struct afs_addr_cursor *ac)
	338	{
fe4d774c DH	339	struct afs_addr_list *alist;
	340
	341	alist = ac->alist;
	342	if (alist) {
	343	if (ac->responded && ac->index != ac->start)
	344	WRITE_ONCE(alist->index, ac->index);
	345	afs_put_addrlist(alist);
	346	}
8b2a464c	347
fe4d774c	348	ac->addr = NULL;
8b2a464c	349	ac->alist = NULL;
fe4d774c	350	ac->begun = false;
8b2a464c DH	351	return ac->error;
	352	}
	353
	354	/*
	355	* Set the address cursor for iterating over VL servers.
	356	*/
	357	int afs_set_vl_cursor(struct afs_addr_cursor ac, struct afs_cell cell)
	358	{
	359	struct afs_addr_list *alist;
	360	int ret;
	361
	362	if (!rcu_access_pointer(cell->vl_addrs)) {
	363	ret = wait_on_bit(&cell->flags, AFS_CELL_FL_NO_LOOKUP_YET,
	364	TASK_INTERRUPTIBLE);
	365	if (ret < 0)
	366	return ret;
	367
	368	if (!rcu_access_pointer(cell->vl_addrs) &&
	369	ktime_get_real_seconds() < cell->dns_expiry)
	370	return cell->error;
	371	}
	372
	373	read_lock(&cell->vl_addrs_lock);
	374	alist = rcu_dereference_protected(cell->vl_addrs,
	375	lockdep_is_held(&cell->vl_addrs_lock));
	376	if (alist->nr_addrs > 0)
	377	afs_get_addrlist(alist);
	378	else
	379	alist = NULL;
	380	read_unlock(&cell->vl_addrs_lock);
	381
	382	if (!alist)
	383	return -EDESTADDRREQ;
	384
	385	ac->alist = alist;
	386	ac->addr = NULL;
	387	ac->start = READ_ONCE(alist->index);
	388	ac->index = ac->start;
	389	ac->error = 0;
	390	ac->begun = false;
	391	return 0;
	392	}