linux-kernel - Re: [PATCH] firewire: adopt read cycle timer ABI from raw1394

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <59ad55d30710010903y76330624ka45747c0b5983cfd@mail.gmail.com>
Date:	Mon, 1 Oct 2007 12:03:23 -0400
From:	"Kristian Høgsberg" <krh@...planet.net>
To:	"Pieter Palmers" <pieterp@...w.be>
Cc:	"Stefan Richter" <stefanr@...6.in-berlin.de>,
	"Kristian Høgsberg" <krh@...hat.com>,
	linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firewire: adopt read cycle timer ABI from raw1394

On 10/1/07, Pieter Palmers <pieterp@...w.be> wrote:
> Stefan Richter wrote:
> >> This duplicates the read cycle timer feature of raw1394 (added in Linux
> >> 2.6.21) in firewire-core's userspace ABI.
> >
> > Kristian and Pieter, does this simple duplication of the ioctl make
> > sense on its own?  AFAIU rawiso's iso packet buffers look different from
> > fw-cdevs's. It seems to me as if rawiso always put the cycle into a user
> > buffer for each iso packet received...
> >
> > raw1394.h::struct raw1394_iso_packet_info {
> >       __u32 offset;
> >       __u16 len;
> >       __u16 cycle;   /* recv only */
> >       __u8  channel; /* recv only */
> >       __u8  tag;
> >       __u8  sy;
> > };
> >
> > raw1394.c::raw1394_iso_recv_packets()
> >
> >       /* copy the packet_infos out */
> >       for (i = 0; i < upackets.n_packets; i++) {
> >               if (__copy_to_user(&upackets.infos[i],
> >                                  &fi->iso_handle->infos[packet],
> >                                  sizeof(struct raw1394_iso_packet_info)))
> >                       return -EFAULT;
> >
> >               packet = (packet + 1) % fi->iso_handle->buf_packets;
> >       }
> >
> > ...while the Juju ABI returns the cycle only for those packets whose
> > fw_cdev_iso_packet.control had the FW_CDEV_ISO_INTERRUPT flag set.
> > The cycle is then written out in the fw_cdev_event_iso_interrupt event
> > which happens when this particular packet was received.  Right?
> >
> > Pieter, do applications like yours need the cycle counter only for a few
> > predetermined packets or for each and every packet?
>
> We need it for every packet for two reasons:
> 1) it's the only way to determine how many packets were dropped when
> packet drops are flagged in the callback

Your application should know what the timestamp should be for each iso
receive callback and if you see a larger value than expected you can
use that to calculate how many cycles were lost.

> 2) we convert the 16-bit SYT timestamp of a packet to a full 32-bit
> cycle counter value. This because the range of the 16-bit SYT is too
> small (only 16 packets) for systems that have large buffering.

If you get the timestamp for the first packet in a receive batch, you
can still do this, right?

cheers,
Kristian
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/