netdev - Re: [PATCH net-next v4] net: dccp: Add SIOCOUTQ IOCTL support (send buffer fill)

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Date:   Fri, 17 Jul 2020 02:56:59 +0200
From:   Richard Sailer <richard_siegfried@...temli.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     gerrit@....abdn.ac.uk, davem@...emloft.net, dccp@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v4] net: dccp: Add SIOCOUTQ IOCTL support (send
 buffer fill)



On 16/07/2020 21:56, Jakub Kicinski wrote:
> On Mon, 13 Jul 2020 00:55:20 +0200 Richard Sailer wrote:
>> This adds support for the SIOCOUTQ IOCTL to get the send buffer fill
>> of a DCCP socket, like UDP and TCP sockets already have.
>>
>> Regarding the used data field: DCCP uses per packet sequence numbers,
>> not per byte, so sequence numbers can't be used like in TCP. sk_wmem_queued
>> is not used by DCCP and always 0, even in test on highly congested paths.
>> Therefore this uses sk_wmem_alloc like in UDP.
>>
>> Signed-off-by: Richard Sailer <richard_siegfried@...temli.org>
> 
> Sorry for the late review
No problem, nothing compared to the information delays at university^^

> 
>> diff --git a/Documentation/networking/dccp.rst b/Documentation/networking/dccp.rst
>> index dde16be044562..74659da107f6b 100644
>> --- a/Documentation/networking/dccp.rst
>> +++ b/Documentation/networking/dccp.rst
>> @@ -192,6 +192,8 @@ FIONREAD
>>  	Works as in udp(7): returns in the ``int`` argument pointer the size of
>>  	the next pending datagram in bytes, or 0 when no datagram is pending.
>>  
>> +SIOCOUTQ
>> +  Returns the number of data bytes in the local send queue.
> 
> FIONREAD uses tabs for indentation, it seems like a good idea to
> document the size of the argument (i.e. "returns in the ``int`` ...").

Agreed
> 
>>  Other tunables
>>  ==============
>> diff --git a/net/dccp/proto.c b/net/dccp/proto.c
>> index c13b6609474b6..dab74e8a8a69b 100644
>> --- a/net/dccp/proto.c
>> +++ b/net/dccp/proto.c
>> @@ -375,6 +375,14 @@ int dccp_ioctl(struct sock *sk, int cmd, unsigned long arg)
>>  		goto out;
>>  
>>  	switch (cmd) {
>> +	case SIOCOUTQ: {
>> +		/* Using sk_wmem_alloc here because sk_wmem_queued is not used by DCCP and
>> +		 * always 0, comparably to UDP.
>> +		 */
>> +		int amount = sk_wmem_alloc_get(sk);
>> +		rc = put_user(amount, (int __user *)arg);
> 
> checkpatch warns:
> 
> WARNING: Missing a blank line after declarations
> #48: FILE: net/dccp/proto.c:383:
> +		int amount = sk_wmem_alloc_get(sk);
> +		rc = put_user(amount, (int __user *)arg);
> 
> Could you please address that, and better still move the declaration of
> "int amount" up to the function level and avoid the funky bracket around
> the case statement altogether?

I found the funky braces disturbing too, but thought they were
convention, so happy to delete them.

Regarding "putting int amount at function level": well the problem is in
the other case statement is a unsigned long (and the pointer in
put_user() is (int __user *) ). I don't yet know if I can make that all
a simple int without losing correctness/security. I will send a v5 when
I figured that out.

Thanks,
-- Richard



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