netdev - Re: [PATCH iproute2] ip route: Set rtm_dst_len to 32 for all ip route get requests

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Message-ID: <35f170ea-d051-3e76-bfa7-1a5259a1d5c8@gmail.com>
Date:   Wed, 22 May 2019 21:42:33 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        David Ahern <dsahern@...nel.org>
Cc:     netdev@...r.kernel.org, Jason@...c4.com
Subject: Re: [PATCH iproute2] ip route: Set rtm_dst_len to 32 for all ip route
 get requests

On 5/22/19 5:16 PM, Stephen Hemminger wrote:
> On Fri, 17 May 2019 10:59:13 -0700
> David Ahern <dsahern@...nel.org> wrote:
> 
>> index 2b3dcc5dbd53..d980b86ffd42 100644
>> --- a/ip/iproute.c
>> +++ b/ip/iproute.c
>> @@ -2035,7 +2035,11 @@ static int iproute_get(int argc, char **argv)
>>  			if (addr.bytelen)
>>  				addattr_l(&req.n, sizeof(req),
>>  					  RTA_DST, &addr.data, addr.bytelen);
>> -			req.r.rtm_dst_len = addr.bitlen;
>> +			/* kernel ignores prefix length on 'route get'
>> +			 * requests; to allow ip to work with strict mode
>> +			 * but not break existing users, just set to 32
>> +			 */
>> +			req.r.rtm_dst_len = 32;
>>  			address_found = true;
>>  		}
>>  		argc--; argv++;
> 
> Why not warn user that any prefix length (ie not 32) is ignored,
> then do what you propose.
> 

My first version did that. I thought people would complain about a
stderr message. At least with failing the 'route get' scripts can be fixed.

After more thought even changing the prefix length for users presents a
limitation on future changes.