From: Paul LeoNerd Evans <leonerd@leonerd.org.uk>
To: Andi Kleen <andi@firstfloor.org>, netdev@vger.kernel.org
Cc: David Miller <davem@davemloft.net>
Subject: Re: RFC: New BGF 'LOOP' instruction
Date: Tue, 3 Aug 2010 15:34:42 +0100 [thread overview]
Message-ID: <20100803143442.GW11110@cel.leo> (raw)
In-Reply-To: <20100803141110.GT11110@cel.leo>
[-- Attachment #1: Type: text/plain, Size: 1287 bytes --]
On Tue, Aug 03, 2010 at 03:11:10PM +0100, Paul LeoNerd Evans wrote:
> switch(hdrtype)
> {
> case 1:
> length = someconst; break;
> case 2:
> length = someotherconst; break;
> case 3:
> length = b[someoffset]; break;
> ...
> }
Of course, I completely forgot about finding also the offset of the
'next header' from the current header. That results in some code which,
in C, would look like:
int hdrtype = b[IPv6_nexthdr];
int x = size_of_IPv6_header;
while(hdrtype != hdr_wanted) {
int len;
switch(hdrtype) {
case 1:
len = someconst;
hdrtype = someotherconst;
break;
case 2:
len = b[x+someoffs];
hdrtype = b[x+someotheroffs];
break;
/* other IPv6 header types here */
}
x += len;
}
You can't compile that idea into BPF without using a scratch memory
cell, because you can't have both 'len' and 'hdrtype' live in A at the
same time, nor can you atomically x += b[x+someoffs].
In short, much much easier if the C code did this part...
--
Paul "LeoNerd" Evans
leonerd@leonerd.org.uk
ICQ# 4135350 | Registered Linux# 179460
http://www.leonerd.org.uk/
[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 190 bytes --]
prev parent reply other threads:[~2010-08-03 14:34 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-02 11:03 RFC: New BGF 'LOOP' instruction Paul LeoNerd Evans
2010-08-02 11:13 ` RFC: New BPF " Paul LeoNerd Evans
2010-08-02 20:16 ` RFC: New BGF " Hagen Paul Pfeifer
2010-08-03 5:18 ` David Miller
2010-08-03 7:07 ` Paul LeoNerd Evans
2010-08-03 7:19 ` David Miller
2010-08-03 9:10 ` Hagen Paul Pfeifer
2010-08-03 13:40 ` Paul LeoNerd Evans
2010-08-03 9:03 ` Hagen Paul Pfeifer
2010-08-03 7:18 ` RFC: New BPF " Paul LeoNerd Evans
2010-08-03 5:13 ` RFC: New BGF " David Miller
2010-08-03 7:04 ` Paul LeoNerd Evans
2010-08-03 7:18 ` David Miller
2010-08-03 12:58 ` Andi Kleen
2010-08-03 13:07 ` David Miller
2010-08-03 13:34 ` RFC: New BPF " Paul LeoNerd Evans
2010-08-03 13:42 ` Paul LeoNerd Evans
2010-08-03 14:09 ` Rémi Denis-Courmont
2010-08-03 14:13 ` Paul LeoNerd Evans
2010-08-03 14:16 ` Rémi Denis-Courmont
2010-08-03 14:19 ` Paul LeoNerd Evans
2010-08-03 15:17 ` Rémi Denis-Courmont
2010-08-03 15:27 ` Paul LeoNerd Evans
2010-08-03 14:05 ` RFC: New BGF " Andi Kleen
2010-08-03 14:11 ` Paul LeoNerd Evans
2010-08-03 14:34 ` Paul LeoNerd Evans [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100803143442.GW11110@cel.leo \
--to=leonerd@leonerd.org.uk \
--cc=andi@firstfloor.org \
--cc=davem@davemloft.net \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).