/*
 * NET          Generic infrastructure for Network protocols.
 *
 *              Definitions for request_sock 
 *
 * Authors:     Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *
 *              From code originally in include/net/tcp.h
 *
 *              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.
 */
#ifndef _REQUEST_SOCK_H
#define _REQUEST_SOCK_H

#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/bug.h>

#include <net/sock.h>

struct request_sock;
struct sk_buff;
struct dst_entry;
struct proto;

struct request_sock_ops {
        int             family;
        int             obj_size;
        struct kmem_cache       *slab;
        char            *slab_name;
        int             (*rtx_syn_ack)(struct sock *sk,
                                       struct request_sock *req);
        void            (*send_ack)(struct sock *sk, struct sk_buff *skb,
                                    struct request_sock *req);
        void            (*send_reset)(struct sock *sk,
                                      struct sk_buff *skb);
        void            (*destructor)(struct request_sock *req);
        void            (*syn_ack_timeout)(struct sock *sk,
                                           struct request_sock *req);
};

int inet_rtx_syn_ack(struct sock *parent, struct request_sock *req);

/* struct request_sock - mini sock to represent a connection request
 */
struct request_sock {
        struct sock_common              __req_common;
        struct request_sock             *dl_next;
        u16                             mss;
        u8                              num_retrans; /* number of retransmits */
        u8                              cookie_ts:1; /* syncookie: encode tcpopts in timestamp */
        u8                              num_timeout:7; /* number of timeouts */
        /* The following two fields can be easily recomputed I think -AK */
        u32                             window_clamp; /* window clamp at creation time */
        u32                             rcv_wnd;          /* rcv_wnd offered first time */
        u32                             ts_recent;
        unsigned long                   expires;
        const struct request_sock_ops   *rsk_ops;
        struct sock                     *sk;
        u32                             secid;
        u32                             peer_secid;
};

static inline struct request_sock *reqsk_alloc(const struct request_sock_ops *ops)
{
        struct request_sock *req = kmem_cache_alloc(ops->slab, GFP_ATOMIC);

        if (req != NULL)
                req->rsk_ops = ops;

        return req;
}

static inline void __reqsk_free(struct request_sock *req)
{
        kmem_cache_free(req->rsk_ops->slab, req);
}

static inline void reqsk_free(struct request_sock *req)
{
        req->rsk_ops->destructor(req);
        __reqsk_free(req);
}

extern int sysctl_max_syn_backlog;

/** struct listen_sock - listen state
 *
 * @max_qlen_log - log_2 of maximal queued SYNs/REQUESTs
 */
struct listen_sock {
        u8                      max_qlen_log;
        u8                      synflood_warned;
        /* 2 bytes hole, try to use */
        int                     qlen;
        int                     qlen_young;
        int                     clock_hand;
        u32                     hash_rnd;
        u32                     nr_table_entries;
        struct request_sock     *syn_table[0];
};

/*
 * For a TCP Fast Open listener -
 *      lock - protects the access to all the reqsk, which is co-owned by
 *              the listener and the child socket.
 *      qlen - pending TFO requests (still in TCP_SYN_RECV).
 *      max_qlen - max TFO reqs allowed before TFO is disabled.
 *
 *      XXX (TFO) - ideally these fields can be made as part of "listen_sock"
 *      structure above. But there is some implementation difficulty due to
 *      listen_sock being part of request_sock_queue hence will be freed when
 *      a listener is stopped. But TFO related fields may continue to be
 *      accessed even after a listener is closed, until its sk_refcnt drops
 *      to 0 implying no more outstanding TFO reqs. One solution is to keep
 *      listen_opt around until sk_refcnt drops to 0. But there is some other
 *      complexity that needs to be resolved. E.g., a listener can be disabled
 *      temporarily through shutdown()->tcp_disconnect(), and re-enabled later.
 */
struct fastopen_queue {
        struct request_sock     *rskq_rst_head; /* Keep track of past TFO */
        struct request_sock     *rskq_rst_tail; /* requests that caused RST.
                                                 * This is part of the defense
                                                 * against spoofing attack.
                                                 */
        spinlock_t      lock;
        int             qlen;           /* # of pending (TCP_SYN_RECV) reqs */
        int             max_qlen;       /* != 0 iff TFO is currently enabled */
};

/** struct request_sock_queue - queue of request_socks
 *
 * @rskq_accept_head - FIFO head of established children
 * @rskq_accept_tail - FIFO tail of established children
 * @rskq_defer_accept - User waits for some data after accept()
 * @syn_wait_lock - serializer
 *
 * %syn_wait_lock is necessary only to avoid proc interface having to grab the main
 * lock sock while browsing the listening hash (otherwise it's deadlock prone).
 *
 * This lock is acquired in read mode only from listening_get_next() seq_file
 * op and it's acquired in write mode _only_ from code that is actively
 * changing rskq_accept_head. All readers that are holding the master sock lock
 * don't need to grab this lock in read mode too as rskq_accept_head. writes
 * are always protected from the main sock lock.
 */
struct request_sock_queue {
        struct request_sock     *rskq_accept_head;
        struct request_sock     *rskq_accept_tail;
        rwlock_t                syn_wait_lock;
        u8                      rskq_defer_accept;
        /* 3 bytes hole, try to pack */
        struct listen_sock      *listen_opt;
        struct fastopen_queue   *fastopenq; /* This is non-NULL iff TFO has been
                                             * enabled on this listener. Check
                                             * max_qlen != 0 in fastopen_queue
                                             * to determine if TFO is enabled
                                             * right at this moment.
                                             */
};

int reqsk_queue_alloc(struct request_sock_queue *queue,
                      unsigned int nr_table_entries);

void __reqsk_queue_destroy(struct request_sock_queue *queue);
void reqsk_queue_destroy(struct request_sock_queue *queue);
void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
                           bool reset);

static inline struct request_sock *
        reqsk_queue_yank_acceptq(struct request_sock_queue *queue)
{
        struct request_sock *req = queue->rskq_accept_head;

        queue->rskq_accept_head = NULL;
        return req;
}

static inline int reqsk_queue_empty(struct request_sock_queue *queue)
{
        return queue->rskq_accept_head == NULL;
}

static inline void reqsk_queue_unlink(struct request_sock_queue *queue,
                                      struct request_sock *req,
                                      struct request_sock **prev_req)
{
        write_lock(&queue->syn_wait_lock);
        *prev_req = req->dl_next;
        write_unlock(&queue->syn_wait_lock);
}

static inline void reqsk_queue_add(struct request_sock_queue *queue,
                                   struct request_sock *req,
                                   struct sock *parent,
                                   struct sock *child)
{
        req->sk = child;
        sk_acceptq_added(parent);

        if (queue->rskq_accept_head == NULL)
                queue->rskq_accept_head = req;
        else
                queue->rskq_accept_tail->dl_next = req;

        queue->rskq_accept_tail = req;
        req->dl_next = NULL;
}

static inline struct request_sock *reqsk_queue_remove(struct request_sock_queue *queue)
{
        struct request_sock *req = queue->rskq_accept_head;

        WARN_ON(req == NULL);

        queue->rskq_accept_head = req->dl_next;
        if (queue->rskq_accept_head == NULL)
                queue->rskq_accept_tail = NULL;

        return req;
}

static inline int reqsk_queue_removed(struct request_sock_queue *queue,
                                      struct request_sock *req)
{
        struct listen_sock *lopt = queue->listen_opt;

        if (req->num_timeout == 0)
                --lopt->qlen_young;

        return --lopt->qlen;
}

static inline int reqsk_queue_added(struct request_sock_queue *queue)
{
        struct listen_sock *lopt = queue->listen_opt;
        const int prev_qlen = lopt->qlen;

        lopt->qlen_young++;
        lopt->qlen++;
        return prev_qlen;
}

static inline int reqsk_queue_len(const struct request_sock_queue *queue)
{
        return queue->listen_opt != NULL ? queue->listen_opt->qlen : 0;
}

static inline int reqsk_queue_len_young(const struct request_sock_queue *queue)
{
        return queue->listen_opt->qlen_young;
}

static inline int reqsk_queue_is_full(const struct request_sock_queue *queue)
{
        return queue->listen_opt->qlen >> queue->listen_opt->max_qlen_log;
}

static inline void reqsk_queue_hash_req(struct request_sock_queue *queue,
                                        u32 hash, struct request_sock *req,
                                        unsigned long timeout)
{
        struct listen_sock *lopt = queue->listen_opt;

        req->expires = jiffies + timeout;
        req->num_retrans = 0;
        req->num_timeout = 0;
        req->sk = NULL;
        req->dl_next = lopt->syn_table[hash];

        write_lock(&queue->syn_wait_lock);
        lopt->syn_table[hash] = req;
        write_unlock(&queue->syn_wait_lock);
}

#endif /* _REQUEST_SOCK_H */