Android/Linux ioctl FIONREAD 失败

Question

我正在将一些(套接字相关的)Windows C 代码移植到 Linux/Android，我遇到了 ioctl 命令的问题:

unsigned long   u;

if(sockfd != -1 && !ioctl(sockfd, FIONREAD, &u))

{
    return((long) u);
}
    ...
// throw exception

当我检查 errno 时，我看到了 EINVAL，但我不明白为什么对 ioctl 的调用因这些参数而失败。我什至试图将 u 声明为 int，但它仍然失败了。我不知道出了什么问题。此代码在 Windows 上运行良好(ioctlsocket 而不是 ioctl)。

这是来自 Linux 的 strace:

socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
bind(3, {sa_family=AF_INET, sin_port=htons(9099), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
listen(3, 5)                            = 0
ioctl(3, FIONREAD, [1])                 = -1 EINVAL (Invalid argument)
write(2, "Exception code: 00000503, data: "..., 52Exception code: 00000503, data: 00000000 ((null):0)
) = 52
shutdown(3, 2 /* send and receive */)   = 0
close(3)                                = 0
exit_group(1)                           = ?

Answer 1

Linux 在监听套接字上不支持 FIONREAD/SIOCINQ。参见 tcp(7) :

SIOCINQ       Returns the amount of queued unread data in the receive buffer.  The       socket must not be in LISTEN state, otherwise an error (EINVAL) is       returned.  SIOCINQ is defined in <linux/sockios.h>.  Alternatively, you       can use the synonymous FIONREAD, defined in <sys/ioctl.h>.