Date: Mon, 20 Apr 2020 20:15:13 -0500 From: Eric van Gyzen <eric@vangyzen.net> To: Shawn Webb <shawn.webb@hardenedbsd.org>, Kristof Provost <kp@FreeBSD.org> Cc: Ronald Klop <ronald-lists@klop.ws>, svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r360068 - in head/sys: kern net sys Message-ID: <523895fb-7f30-c4ce-78a7-d16b2ff4954c@vangyzen.net> In-Reply-To: <20200419142327.nhotyboqubk3vl2l@mutt-hbsd> References: <202004180750.03I7oUK6032898@repo.freebsd.org> <op.0jbpatnnkndu52@sjakie> <67B55A62-848B-4876-8367-DE0D32A8B7D4@FreeBSD.org> <20200419142327.nhotyboqubk3vl2l@mutt-hbsd>
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>>>> + sz = asprintf(&buf, M_TEMP, "%s-%s-%s", uuid, if_name(ifp),
>>>> + jailname);
>>>> + if (sz < 0) {
>>>> + /* Fall back to a random mac address. */
>>>
>>>
>>> I was wondering if it would be valuable to give this fall back something
>>> like:
>>>
>>> printf("%s: unable to create fixed mac address; using random
>>> mac address", if_name(ifp));
>>>
>>> This will only be printed in rare circumstances. But in that case will
>>> provide valuable information.
>>>
>> That would potentially be valuable, yes. On the other hand, we traditionally
>> don???t sprinkle a lot of printf()s around in the kernel. This is extremely
>> unlikely to happen, and if it does odds are attaching the interface will
>> fail at an earlier or later point, you may struggle to pass packets and run
>> into any number of other issues.
>> It???s also possible to diagnose absent the printf(), because the MAC
>> address will be locally administered rather than within the FreeBSD OUI.
>>
>> So, in short: not a bad idea. You can argue it both ways, and I find myself
>> (weakly) on the opposite side.
>
> Would displaying the message only when verbose boot mode is enabled be
> a suitable compromise?
We could completely avoid the problems of dynamic allocation by calling
SHA1Update three times, feeding each piece of data separately.
For bonus points, use a single char[] to save stack space, too. Maybe
use a union, for legibility, and to ensure the proper size without ugly
assertions.
Eric
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