/* Server address list management
 *
 * Copyright (C) 2017 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 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(sizeof(*alist) + sizeof(alist->addrs[0]) * 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];
                char tdelim = delim;

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

                if (*p == '[') {
                        p++;
                        tdelim = ']';
                }

                if (in4_pton(p, end - p,
                             (u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
                             tdelim, &p)) {
                        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, end - p,
                                    srx->transport.sin6.sin6_addr.s6_addr,
                                    tdelim, &p)) {
                        /* Nothing to do */
                } else {
                        goto bad_address;
                }

                if (tdelim == ']') {
                        if (p == end || *p != ']')
                                goto bad_address;
                        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,
                        "ipv4", &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] &&
                    xport < a->sin6_port)
                        break;
                if (xdr < 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 &&
                    xport < 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)
{
        if (ac->responded && ac->index != ac->start)
                WRITE_ONCE(ac->alist->index, ac->index);

        afs_put_addrlist(ac->alist);
        ac->alist = NULL;
        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;
}