percent_expand for QoS in ControlPath

[Saku Ytti]

I'm not sure if I understand what is suggested here, but I think it
might be that in ControlMaster scenario some packets would be sent
with different TOS value than another.

But I don't think it actually matters, consider you're having
interactive ssh session to remote host from your PC behind ADSL, all
good. Then you upload large file from your PC to the same remote host.
Now without ControlMaster all is well, with proper TOS values in
packets, interactive session won't become laggy, but in ControlMaster
it will. And I don't understand how it could be solved, as TCP
guarantees at kernel level ordering of packets, so even if your ADSL
CPE reorders the packets and sends the high priority interactive ssh
packets first the remote host kernel will not give them to userland
until original order has restored, essentially rendering the
prioritization done in the ADSL CPE useless.

(This is practical example of problem I run into weekly, I workaround
it by setting ControlPath none for scp)

On 30 March 2012 02:01, Jared Yanovich <slovichon at gmail.com> wrote:
> Hi,
>
> Not sure if this anyone else is interested in this but to me it seems to make
> sense to use different control session multiplexer sockets for bulk and
> interactive workloads.
>
> Index: auth.c
> ===================================================================
> RCS file: /cvs/src/usr.bin/ssh/auth.c,v
> retrieving revision 1.94
> diff -u -p -r1.94 auth.c
> --- auth.c      23 May 2011 03:33:38 -0000      1.94
> +++ auth.c      29 Mar 2012 23:00:06 -0000
> @@ -326,7 +326,7 @@ check_key_in_hostfiles(struct passwd *pw
>  *
>  * XXX Should any specific check be done for sym links ?
>  *
> - * Takes an open file descriptor, the file name, a uid and and
> + * Takes an open file descriptor, the file name, a uid and an
>  * error buffer plus max size as arguments.
>  *
>  * Returns 0 on success and -1 on failure
> Index: ssh.c
> ===================================================================
> RCS file: /cvs/src/usr.bin/ssh/ssh.c,v
> retrieving revision 1.368
> diff -u -p -r1.368 ssh.c
> --- ssh.c       24 Oct 2011 02:10:46 -0000      1.368
> +++ ssh.c       29 Mar 2012 23:00:06 -0000
> @@ -701,7 +701,7 @@ main(int ac, char **av)
>                options.port = sp ? ntohs(sp->s_port) : SSH_DEFAULT_PORT;
>        }
>
> -       /* preserve host name given on command line for %n expansion */
> +       /* preserve host name given on command line for %h expansion */
>        host_arg = host;
>        if (options.hostname != NULL) {
>                host = percent_expand(options.hostname,
> @@ -750,6 +750,8 @@ main(int ac, char **av)
>                options.control_path = percent_expand(cp, "h", host,
>                    "l", thishost, "n", host_arg, "r", options.user,
>                    "p", portstr, "u", pw->pw_name, "L", shorthost,
> +                   "Q", iptos2str(tty_flag ?
> +                     options.ip_qos_interactive : options.ip_qos_bulk),
>                    (char *)NULL);
>                xfree(cp);
>        }
> Index: ssh_config.5
> ===================================================================
> RCS file: /cvs/src/usr.bin/ssh/ssh_config.5,v
> retrieving revision 1.154
> diff -u -p -r1.154 ssh_config.5
> --- ssh_config.5        9 Sep 2011 00:43:00 -0000       1.154
> +++ ssh_config.5        29 Mar 2012 23:00:06 -0000
> @@ -313,23 +313,30 @@ in the
>  section above or the string
>  .Dq none
>  to disable connection sharing.
> -In the path,
> -.Ql %L
> -will be substituted by the first component of the local host name,
> -.Ql %l
> -will be substituted by the local host name (including any domain name),
> -.Ql %h
> -will be substituted by the target host name,
> -.Ql %n
> -will be substituted by the original target host name
> -specified on the command line,
> -.Ql %p
> -the port,
> -.Ql %r
> -by the remote login username, and
> -.Ql %u
> -by the username of the user running
> -.Xr ssh 1 .
> +.Pp
> +In the path, the following substitutions are recognized:
> +.Pp
> +.Bl -tag -width 3n -compact -offset 2n
> +.It \&%h
> +target host name
> +.It \&%L
> +first component of the local host name
> +.It \&%l
> +local host name (including any domain name)
> +.It \&%n
> +original target host name specified on the command line
> +.It \&%p
> +port
> +.It \&%Q
> +quality of service string
> +.Pq e.g. Dq lowdelay
> +.It \&%r
> +remote login username
> +.It \&%u
> +username of the user running
> +.Xr ssh 1
> +.El
> +.Pp
>  It is recommended that any
>  .Cm ControlPath
>  used for opportunistic connection sharing include
> _______________________________________________
> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev



-- 
  ++ytti