svn commit: r254524 - head/sys/sys

[Davide Italiano]

On Tue, Aug 20, 2013 at 7:42 PM, Andre Oppermann <andre at freebsd.org> wrote:
> On 19.08.2013 19:37, Navdeep Parhar wrote:
>>
>> On 08/19/13 06:56, Andre Oppermann wrote:
>>>
>>> Author: andre
>>> Date: Mon Aug 19 13:56:14 2013
>>> New Revision: 254524
>>> URL: http://svnweb.freebsd.org/changeset/base/254524
>>>
>>> Log:
>>>    Add four additional M_PROTOFLAGS[9-12] for protocol specific use.
>>>
>>>    Discussed with:      trociny, glebius, adrian
>>>
>>> Modified:
>>>    head/sys/sys/mbuf.h
>>>
>>> Modified: head/sys/sys/mbuf.h
>>>
>>> ==============================================================================
>>> --- head/sys/sys/mbuf.h Mon Aug 19 13:27:32 2013        (r254523)
>>> +++ head/sys/sys/mbuf.h Mon Aug 19 13:56:14 2013        (r254524)
>>> @@ -196,22 +196,24 @@ struct mbuf {
>>>   #define       M_FRAG          0x00000800 /* packet is a fragment of a
>>> larger packet */
>>>   #define       M_FIRSTFRAG     0x00001000 /* packet is first fragment */
>>>   #define       M_LASTFRAG      0x00002000 /* packet is last fragment */
>>> -                    /* 0x00004000    free */
>>> -                    /* 0x00008000    free */
>>> +#define        M_PROTO9        0x00004000 /* protocol-specific */
>>> +#define        M_PROTO10       0x00008000 /* protocol-specific */
>>>   #define       M_VLANTAG       0x00010000 /* ether_vtag is valid */
>>>   #define       M_PROMISC       0x00020000 /* packet was not for us */
>>> -                    /* 0x00040000    free */
>>> +#define        M_PROTO11       0x00040000 /* protocol-specific */
>>>   #define       M_PROTO6        0x00080000 /* protocol-specific */
>>>   #define       M_PROTO7        0x00100000 /* protocol-specific */
>>>   #define       M_PROTO8        0x00200000 /* protocol-specific */
>>>   #define       M_FLOWID        0x00400000 /* deprecated: flowid is valid
>>> */
>>> +#define        M_PROTO12       0x00800000 /* protocol-specific */
>>>   #define       M_HASHTYPEBITS  0x0F000000 /* mask of bits holding flowid
>>> hash type */
>>
>>
>> Why reuse the freed up bits so soon (at least one of which I think was
>> prematurely GC'ed -- see my other email on M_NOFREE).  There was room
>> beyond M_HASHTYPEBITS, no?
>
>
> This is HEAD where kernel and modules have to be (re)compiled together
> at any point in time.  On stable this reuse would not have been possible.
>
> In a subsequent commit I compacted and ordered the flags.  There's a couple
> of free ones remaining.
>
> I have some additional mbuf changes coming up to be posted for possible
> objections later today.  The close HEAD freeze deadline has got me rushed
> a bit to allow 10.x backporting of the checksum/offload overhaul.
>
> --
> Andre
>

In my opinion the possibility we have about breaking KPI/KBI should
not be abused, even if it's allowed in HEAD. In other words,people
should go for preserving it  when (as in this case) it's easy and
without additional costs. Your point about "this is HEAD, it can be
broken at any time" makes relatively little sense  to me. Note that in
the worst case such KPI/KBI breakages are annoying for $VENDORS who
maintain out-of-tree code, which need to rebuild/change their code,
or, if they get pissed off, drop FreeBSD support.
In your case, it's just a matter of "code cleaness" about few lines,
which, IMHO and always IMHO, doesn't justify the breakage.

Thanks,

-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare