[net,v2,1/1] net: tcp: Permit user set TCP_MAXSEG to default value

From: Gao Feng <fgao@ikuai8.com>

When user_mss is zero, it means use the default value. But the current
codes don't permit user set TCP_MAXSEG to the default value.
It would return the -EINVAL when val is zero.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
---
 v2: Make codes more clearer, per Eric
 v1: initial version

 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Mon, Mar 20, 2017 at 8:45 PM, <fgao@ikuai8.com> wrote:
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 1e319a5..4f7f163 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2470,7 +2470,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
>                 /* Values greater than interface MTU won't take effect. However
>                  * at the point when this call is done we typically don't yet
>                  * know which interface is going to be used */
> -               if (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW) {
> +               if (!val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW)) {
>                         err = -EINVAL;
>                         break;

I believe the sense of the val check is flipped in the proposed patch.

I believe Eric suggested:

  if (val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW)) {

Has this been tested?

neal

On Tue, Mar 21, 2017 at 9:23 AM, Neal Cardwell <ncardwell@google.com> wrote:
> On Mon, Mar 20, 2017 at 8:45 PM, <fgao@ikuai8.com> wrote:
>> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
>> index 1e319a5..4f7f163 100644
>> --- a/net/ipv4/tcp.c
>> +++ b/net/ipv4/tcp.c
>> @@ -2470,7 +2470,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
>>                 /* Values greater than interface MTU won't take effect. However
>>                  * at the point when this call is done we typically don't yet
>>                  * know which interface is going to be used */
>> -               if (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW) {
>> +               if (!val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW)) {
>>                         err = -EINVAL;
>>                         break;
>
> I believe the sense of the val check is flipped in the proposed patch.
>
> I believe Eric suggested:
>
>   if (val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW)) {
>
> Has this been tested?
>
> neal

Sorry, I missed the test this time because of the minor fix.
As a result, wrote the wrong logic.

Regards
Feng