On Thu, Jan 20, 2022 at 07:08:03AM -0800, Andrea Bolognani wrote: > On Thu, Jan 20, 2022 at 01:33:01PM +0000, Daniel P. Berrangé wrote: > > # virsh dumpxml fedora34x86_64 | xmllint -xpath '/domain/devices/console[2]' - > > <console type="pty"> > > <target type="isa-debug" port="1"/> > > <address type="isa" iobase="0x402"/> > > </console> > > I can't force myself to page all of the context back in right now, > but last time we discussed adding support for isa-debugcon back in > 2019 Gerd seemed to be pretty firmly against using <console>. > > https://listman.redhat.com/archives/libvir-list/2019-January/msg01045.html Heh, I totally forgot that we have that discussion previously. I can totally rule out <channel> as a concept as I think that has very specific semantics around being targetted for supporting explicit application network protocols. This just doesn't fit into it nicely. The choice is <console> vs <serial> vs <new_invented_thing> I briefly considered <new_invented_thing/> but I didn't feel it was justifiable to introduce a new type of element. My thought was it could be a <debugger> element, which could support both this firmware debug console and QEMU's GDB stub, both of which are chardev based. The overhead of new parsing, support in virsh console, and so on felt uncessarily high, and the overlap with GDB wasn't clearcut. Even though it is used for debug purposes for getting data out of the firmware, it is a very different beast from thue GDB debugger stub. eg GDB is for running a communication protocol while this is just a text output stream. In fact the GDB stub could indeed be a good fit for <channel> because it is basically a network protocol.[ To me I think of <console> as exclusively reflecting a text I/O channel targetting humans, while <serial> is a more general purpose data channel that can be used for multiple purposes. Either running app protocols or for plain text console I/O. In terms of an low level implementation isa-debugcon could be argued to be a general purpose (unidirectional) data channel, that is just passing arbitrary bytes. That would push towards <serial> as a mapping In terms of the actual real world use cases though, isa-debugcon is (AFAIK) only used for spewing text debugging messages aimed at humans. That pushes towards <console> as a mapping. On balance I felt <console> was/is the winner. Essentially every impl of <console> can be said to be a general purpose data channel for passing arbitrary bytes. We choose to explicitly distinguish <console> from <serial> based on the intended use case of the thing. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
