[Devel] Re: [DRAFT] Container mini-summit notes v0.01

[sukadev at us.ibm.com]

Oren Laadan [orenl at cs.columbia.edu] wrote:
| 
| (sorry from the delay, been away :)
| 
| Eric W. Biederman wrote:
| > "Serge E. Hallyn" <serue at us.ibm.com> writes:
| > 
| >> Sorry, I was focusing on the virtual server needs.
| >>
| >> devpts is it's own fs so I was fully expecting to make it mountable
| >> multiple times so a container can have it's own /dev/pts/0.  So what
| >> other virtual devices would we want to be able to rec-reate for a
| >> migrated application?  (I wonder (a) what gregkh will say about having
| >> a device namespace, and (b) what the sysfs implications will be)
| > 
| > Depends.  There are things like the loop device that could be interesting.
| > There may be some others.  I haven't looked at it enough detail to get
| > beyond the fact that in some sense it isn't just limited to pts devices.
| > 
| > A multimount devpts is interesting though.
| 
| Devices I had to deal with (in zap) so far - to be able to ckpt/restart
| (and migrate) a desktop session:
| 
| * /dev/rtc  (e.g. for mplayer)
| 
| * /dev/dsp
| 
| * /dev/random ?  (to isolate entropy pools ?)
| 
| * virtual consoles - e.g. in zap, an X server that uses a virtual device
| runs inside a pod/container/VE (and X per-se requires a virtual console)
| 
| * virtual terminals - e.g. in zap we allow access to a pod from the host
| without a need to run 'sshd' inside and setup a network in the pod. (Then
| with a suitable utility and network access to the host, this also allows
| sort of remote (a-la serial) console access).
| >From inside the pod it looks like /dev/tty{1,2,..}, so one can run 'getty'
| processes inside the pod. From the outside (for the admin, e.g.) it is an
| extended /dev/tty that has an extra ioctl to multiplex access, so the
| admin (program) can ask to be connected to tty X of pod Y, and it will
| connect to that console (like connecting via serial line).

This sounds really interesting. Were these devices part of a complete
device namespace ?  IOW, does say /dev/tty2 in each pods have the same
major/minor number (4,2) ? Does each '/dev/tty2' have a separate entry
in sysfs ?


| The main advantage is that as a virtual device it can be migrated (with
| its buffers, if not empty, as they reside inside the pod) so upon restart
| they go with the 'getty' processes that use them. The (old) admin will
| see the line dropped, and the (new) admin after the migration can connect
| at the new machine.
| 
| Oren.
| 
| 
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