Hi, Johannes,
thanks for ideas sharing.
>> definitely so. while there are something «around» process - e.g. a
>> way to execute process inside existing container, error handling/etc
>
> In my view, a container maps in Genode to a subsystem (comprising a VFS
> server and other infrastructure). Hence, starting a process inside an
> existing container should be pretty straightforward.
…
>
> I believe sharing code pages in Genode would be a matter of the parent
> component who sets up the children's address spaces. Currently, we use
> the sandbox library for this.
I assume that this sharing implemented on the edge between file system and page
cache (at least this is true for Linux/unix and Windows)
in that case we need to have single VFS server with own cache/page mapping for
files being shared between different instance of containers (subsystems), not
only for children’s?
is it true for current implementation of [single VFS+FS server] <=> [[multiple
subsystems]]?
>>
>> if we want to share effectively files they should be visible with the
>> same «inode» (or similar, depending upon a file system) then instance
>> of file system should be visible from every container via single FS
>> instance. it should handle COW as well.
>
> I think this is exactly what a VFS server component does. It
> provides a File_system service to which multiple components can
> connect.
>
do you have an example of implementation of combination of VFS+FS server and a
set of subsystems (at least 2) connected to the single server instance?
>>
>>>> 3. Implementing a container runtime for Genode that sets up a
>>> sub-init to launch the container process with the appropriate VFS
>>> and helper components according to the container configuration.
>>
>> again, same question like above. typically you could use something
>> like tinit (tiny init) for such purposes, while it is not mandatory
>> and for many apps it will work without. but you need to understand
>> what will be with child processes inside container, who will own them
>> after death of parent (or this should not happens and you can use app
>> itself as pseudo init).
>
> Sorry, I was not crystal clear in my terminology. By "sub-init", I meant
> Genode's init component that we use for spawning subsystems.
> Honestly, I haven't spent any thought on multi-process containers. I
> had the impression that most commonly a container merely runs a single
> process, i.e. does not spawn new processes on its own.
this is not exactly true. while initially containers was developed with such an
idea, later it became more complex
imagine build container - it run make inside (which fork gcc which in turn fork
cpp then cc1 then as then ls and may be ar/ranlib/objcopy/etc)
and if you have make -j4 - then make will run 4 parallel compilation (if
Makefile allows). they must use the same file system instance (volume) to
process intermediate files like .c -> .i -> .s -> .o -> .out...
returning back to genode and subsystems.
how it is implemented in this moment , e.g. how make (native) can run inside
genode noux?
probably it use libc fork()/exec()/etc together with pthreads?
do the processes (threads in genode terminology) share something bu default
after start?
can I run a bunch of «processes» inside genode in single subsystem which share
some services from outside (like VFS+FS)?
more interesting question - do they share single swapping to disk service if
need?
or every subsystem has own pager with own page file?
I think that if I will have examples of implementation of these features in the
way which will be suitable for genode subsystem-per-container model then we can
have docker on genode relatively fast.
Sincerely,
Alexander
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