request_sock.h

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/*
 * NET      Generic infrastructure for Network protocols.
 *
 *      Definitions for request_sock 
 *
 * Authors: Arnaldo Carvalho de Melo <[email protected]>
 *
 *      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;

/* empty to "strongly type" an otherwise void parameter.
 */
struct request_values {
};

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,
                       struct request_values *rvp);
    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);
};

/* struct request_sock - mini sock to represent a connection request
 */
struct request_sock {
    struct request_sock     *dl_next; /* Must be first member! */
    u16             mss;
    u8              retrans;
    u8              cookie_ts; /* syncookie: encode tcpopts in timestamp */
    /* 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 {
    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 {
    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.
                         */
};

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

extern void __reqsk_queue_destroy(struct request_sock_queue *queue);
extern void reqsk_queue_destroy(struct request_sock_queue *queue);
extern 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->retrans == 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->retrans = 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 */