Re: [Libguestfs] [v2v PATCH v2] convert_linux: translate the first CD-ROM's references in boot conf files

On Thu, Dec 16, 2021 at 12:12:33PM +0100, Laszlo Ersek wrote: This does indeed seem like a new problem (in LVM). I don't think we've seen this one before so it needs a bug to track it. About the patch: The fact that there's an existing bug does not block this patch from going upstream. It doesn't seem as if this patch is the cause. About device name translation: This is something of a mess at the moment. There's a lot of history ... Originally I didn't think very deeply about how device names should be represented in the API. For example if you had an API like int guestfs_mount (guestfs_h *g, char *device, char *mp) how should the device name be represented? In the original version it was basically the QEMU / kernel name, probably "/dev/vda1". When we switched to using virtio-scsi the device names changed ("/dev/sda1"), but that was fine I just added some code which spotted /dev/[hsv]... and translated it inside the daemon. (This is what "device name translation" does). Informally I said that "/dev/sda" in the API means the "first disk", (in the sense of "added first using guestfs_add_drive") "/dev/sdb" means second disk, "/dev/sda4" means the fourth partition of the first disk and so on. This was a convention but it wasn't encoded or enforced anywhere. That all worked for quite a long time, but then the kernel started to enumerate devices in parallel, so now if you two disks, you could no longer assume that the "first disk" might randomly appear as /dev/sda or /dev/sdb. We're still sending these strings across from the library to the daemon, but now we do some additional and very hokey translation using device serial numbers which you can check in the code (daemon/device-name-translation.c) I think what we _should_ be doing is translating the strings into an internal representation, which we'd use inside the library and serialise into the daemon. This is, naturally, an awful lot of work. Note that the ABI cannot be changed, so whatever happens we're still going to be passing strings to guestfs_* APIs, this is all about what happens internally after that point in the generated code. There's the additional complication that not everything mountable is a disk (eg. LVs, /dev/md*). Matt Booth already separated that out with a distinction between disks and "mountables". There's also the issue that we always add a hidden disk for the appliance, which is added after the other drives. We need to ignore that. There's also disk hotplugging which we should deprecate - it was a failed experiment, and indeed has never worked for the direct backend which is enough justification to replace those APIs with ones which print an error and return -1. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v