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112 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
113 {
114         const struct tcp_timewait_sock *tcptw = tcp_twsk(sktw);
115         struct tcp_sock *tp = tcp_sk(sk);
116
117         /* With PAWS, it is safe from the viewpoint
118            of data integrity. Even without PAWS it is safe provided sequence
119            spaces do not overlap i.e. at data rates <= 80Mbit/sec.
120
121            Actually, the idea is close to VJ's one, only timestamp cache is
122            held not per host, but per port pair and TW bucket is used as state
123            holder.
124
125            If TW bucket has been already destroyed we fall back to VJ's scheme
126            and use initial timestamp retrieved from peer table.
127          */
128         if (tcptw->tw_ts_recent_stamp &&
129             (twp == NULL || (sysctl_tcp_tw_reuse &&
130                              get_seconds() - tcptw->tw_ts_recent_stamp > 1))) {
131                 tp->write_seq = tcptw->tw_snd_nxt + 65535 + 2;
132                 if (tp->write_seq == 0)
133                         tp->write_seq = 1;
134                 tp->rx_opt.ts_recent       = tcptw->tw_ts_recent;
135                 tp->rx_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
136                 sock_hold(sktw);
137                 return 1;
138         }
139
140         return 0;
141 }