linux系统调用Author：阿冬哥Created：201

疑惑1：通过setsockopt设置SO_SNDBUF、SO_RCVBUF这连个默认缓冲区的，再用getsockopt获取设置的，发现返回是设置的两倍。为什么？

通过网上查找，看到linux的内核代码/usr/src/linux-2.6.13.2/net/core/sock.c，找到sock_setsockopt这个函数的这段代码：

caseSO_SNDBUF: /* Don't error on this BSD doesn't and if you think about it this is right。 Otherwise apps have to play 'guess the biggest size' games。 RCVBUF/SNDBUF are treated in BSD as hints */ if (val > sysctl_wmem_max)//val是我们想设置的缓冲区大小的 val = sysctl_wmem_max;//大于最大，则val设置成最大 sk->sk_userlocks |= SOCK_SNDBUF_LOCK; if ((val * 2) < SOCK_MIN_SNDBUF)//val的两倍小于最小，则设置成最小 sk->sk_sndbuf = SOCK_MIN_SNDBUF; else sk->sk_sndbuf = val * 2;//val的两倍大于最小，则设置成val的两倍 /* * Wake up sending tasks if we * upped the value。

*/ sk->sk_write_space(sk); break; caseSO_RCVBUF: /* Don't error on this BSD doesn't and if you think about it this is right。 Otherwise apps have to play 'guess the biggest size' games。 RCVBUF/SNDBUF are treated in BSD as hints */ if (val > sysctl_rmem_max) val = sysctl_rmem_max; sk->sk_userlocks |= SOCK_RCVBUF_LOCK; /* FIXME: is this lower bound the right one? */ if ((val * 2) < SOCK_MIN_RCVBUF) sk->sk_rcvbuf = SOCK_MIN_RCVBUF; else sk->sk_rcvbuf = val * 2; break;

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