netdev - Re: [RFC iproute2] tos: interpret ToS in natural numeral system

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Date:   Wed, 16 Feb 2022 18:52:43 -0700
From:   David Ahern <dsahern@...il.com>
To:     Guillaume Nault <gnault@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     stephen@...workplumber.org, netdev@...r.kernel.org
Subject: Re: [RFC iproute2] tos: interpret ToS in natural numeral system

On 2/16/22 3:23 PM, Guillaume Nault wrote:
> On Wed, Feb 16, 2022 at 11:42:05AM -0800, Jakub Kicinski wrote:
>> Silently forcing a base numeral system is very painful for users.
>> ip currently interprets tos 10 as 0x10. Imagine user's bash script
>> does:
>>
>>   .. tos $((TOS * 2)) ..
>>
>> or any numerical operation on the ToS.
>>
>> This patch breaks existing scripts if they expect 10 to be 0x10.
> 
> I agree that we shouldn't have forced base 16 in the first place.
> But after so many years I find it a bit dangerous to change that.

I agree. In this case the change in behavior will not be very obvious
and could lead to confusion. I think this is something we have to live with.

> 
> What about just printing a warning when the value isn't prefixed with
> '0x'? Something like (completely untested):
> 
> @@ -535,6 +535,12 @@ int rtnl_dsfield_a2n(__u32 *id, const char *arg)
>  	if (!end || end == arg || *end || res > 255)
>  		return -1;
>  	*id = res;
> +
> +	if (strncmp("0x", arg, 2))
> +		fprintf(stderr,
> +			"Warning: dsfield and tos parameters are interpreted as hexadecimal values\n"
> +			"Use 'dsfield 0x%02x' to avoid this message\n", res);
> +
>  	return 0;
>  }

That seems reasonable to me to let users know of this behavior.

> 
> 
>> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
>> --
>> I get the feeling this was discussed in the past.
>>
>> Also there's more:
>>
>> devlink/devlink.c:	val = strtoull(str, &endptr, 10);
>> devlink/devlink.c:	val = strtoul(str, &endptr, 10);
>> devlink/devlink.c:	val = strtoul(str, &endptr, 10);
>> devlink/devlink.c:	val = strtoul(str, &endptr, 10);

I think the devlink ones all check out. I think those functions can be
updated to use get_uNN from lib/utils.c.

>> lib/utils.c:	res = strtoul(arg, &ptr, base);

This is get_unsigned and those users outside of tc look ok.

>> lib/utils.c:		n = strtoul(cp, &endp, 16);

ipv6 address conversion which is hex based.

>> lib/utils.c:		tmp = strtoul(tmpstr, &endptr, 16);
>> lib/utils.c:		tmp = strtoul(arg + i * 3, &endptr, 16);

both of these are valid hex conversions


>> misc/lnstat_util.c:			unsigned long f = strtoul(ptr, &ptr, 16);
>> tc/f_u32.c:	htid = strtoul(str, &tmp, 16);
>> tc/f_u32.c:		hash = strtoul(str, &tmp, 16);
>> tc/f_u32.c:			nodeid = strtoul(str, &tmp, 16);
>> tc/tc_util.c:	maj = strtoul(str, &p, 16);
>> tc/tc_util.c:	maj = strtoul(str, &p, 16);
>> tc/tc_util.c:		min = strtoul(str, &p, 16);
> 
> After a very quick look, many of these seem to make sense though. For
> example lnstat_util.c parses output from /proc, hexstring_a2n() is used
> by ipmacsec.c to parse crypto keys, etc.
> 
> But I agree that we should probably audit the strtol() (and variants)
> that don't use base 0.

Added Jamal and Cong for the tc references. Hopefully those are
documented to be hex values.