Paolo Bonzini <pbonz...@redhat.com> writes: > On 23/01/2017 10:48, Markus Armbruster wrote: >> The PC machines (pc-q35-* pc-i440fx-* pc-* isapc xenfv) automatically >> create lsi53c895a SCSI HBAs and SCSI devices to honor -drive if=scsi. >> For giggles, try -drive if=scsi,bus=25,media=cdrom --- this makes QEMU >> create 25 of them. >> >> The lsi53c895a is thoroughly obsolete (PCI Ultra2 SCSI, ca. 2000), and >> currently has no maintainer in QEMU. megasas is a better choice, >> except for old OSes, which lack drivers. virtio-scsi is a much better >> choice when you have a driver, but only (newish) Linux comes with one >> in the box. There is no good default that works for all guests. >> >> Instead of supplying the not-so-good default just because we've always >> supplied it, make the user pick, by not creating any SCSI HBAs for >> -drive if=scsi. The user now needs to create the SCSI HBA himself >> with -device. The SCSI devices will still be created automatically. >> >> For backward compatibility, keep the traditional behavior for old >> machine types. > > It would print an "orphaned device" message, right?
Yes. Before this patch, you can't get an "orhpaned" warning for if=scsi with a PC machine. After this patch, you get one for every if=scsi with new PC machine types. > Could we change > those messages to errors Fine with me, but when it comes to arguing for backward compatibility of our byzantine command line, I'm kind of like a lethargic public defender with an overly deep relationship to Bourbon. "Your honor, sure capital punishment is called for? Yes? Okay then." I vaguely recall discussing the topic with Peter (cc'ed). If memory serves, one concern was breaking usage of -device with -drive lacking if=... Works fine (no warning) with machines that don't pick up drives with their default block interface type, i.e. most of them. But PATCH 3 changes their default to if=none, so that usage wouldn't actually break. What would break is -device with -drive if=T, where T is not none and not picked up by the board. Such usage is certainly questionable[*], but it's questionable enough for us to break it? > and then drop PC if=scsi support altogether? Different backward compatibility question: here we break usage of if=scsi with PC machine types. Legacy way to do things, but it's documented in qemu.1. Are we happy to break it? [*] Here's my review of a prior attempt to outlaw it: http://lists.gnu.org/archive/html/qemu-devel/2015-06/msg03334.html
