From: Chris Friesen <chris.friesen@genband•com>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: Stephen Hemminger <stephen@networkplumber•org>,
netdev <netdev@vger•kernel.org>
Subject: Re: why is it not allowed to add a new socket protocol family as an external module?
Date: Thu, 21 Feb 2013 09:47:33 -0600 [thread overview]
Message-ID: <51264195.9060800@genband.com> (raw)
In-Reply-To: <1361410797.17413.3.camel@edumazet-glaptop>
On 02/20/2013 07:39 PM, Eric Dumazet wrote:
> On Wed, 2013-02-20 at 18:44 -0600, Chris Friesen wrote:
>
>> Yes, there are a number of tables sized by NPROTO/AF_MAX/PF_MAX (and the
>> fact that we use all three within the kernel is kind of sad) but there
>> is no technical reason why we couldn't extend those dynamically if
>> desired (with a linked list of additional protocols, perhaps).
>>
>> Hence my question--is the restriction for an ideological reason or
>> simply because nobody thought it was worth the effort?
>>
>
> I guess nobody did the preliminary work.
>
> lockdep might be the tricky part.
>
> net/core/sock.c:197:static const char *const af_family_key_strings[AF_MAX+1] = {
> net/core/sock.c:211: "sk_lock-AF_NFC" , "sk_lock-AF_MAX"
> net/core/sock.c:213:static const char *const af_family_slock_key_strings[AF_MAX+1] = {
> net/core/sock.c:227: "slock-AF_NFC" , "slock-AF_MAX"
> net/core/sock.c:229:static const char *const af_family_clock_key_strings[AF_MAX+1] = {
> net/core/sock.c:243: "clock-AF_NFC" , "clock-AF_MAX"
> net/core/sock.c:250:static struct lock_class_key af_callback_keys[AF_MAX];
Unless I'm missing something that looks straightforward.
When registering dynamically the new protocol would need to specify one
string, the protocol name. ("AF_MYPROTOCOL" or something). The three
key strings are derived from that.
The three lock_class_key structs (corresponding to
af_family_keys/af_family_slock_keys/af_callback_keys) can be
auto-allocated by the network core at dynamic registration time.
sock_lock_init(), sk_clone_lock(), and sock_init_data() would need
special-casing for protocol number larger than AF_MAX. The most
readable would probably be to do the mapping from family to key/string
in helper functions rather than hard-coding a table offset right in
these routines.
Yes, there would be a runtime penalty, but it should be minimal. For
static protocols it would be a few "sk->sk_family < AF_MAX" checks. For
dynamic protocols they might need to walk a linked list, which in all
probability would be very short.
Chris
next prev parent reply other threads:[~2013-02-21 15:47 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-20 16:56 why is it not allowed to add a new socket protocol family as an external module? Chris Friesen
2013-02-20 23:23 ` Stephen Hemminger
2013-02-21 0:44 ` Chris Friesen
2013-02-21 1:05 ` David Miller
2013-02-21 15:19 ` Chris Friesen
2013-02-21 1:39 ` Eric Dumazet
2013-02-21 15:47 ` Chris Friesen [this message]
2013-02-21 16:04 ` Stephen Hemminger
2013-02-21 16:19 ` Chris Friesen
2013-02-21 16:43 ` Eric Dumazet
2013-02-21 17:58 ` Chris Friesen
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