[pve-devel] [PATCH qemu-server 2/2] fix #4620: cfg2cmd: drive device: correctly handle IDE for q35

[Fiona Ebner <f.ebner@proxmox.com>]

Only unit 0 for IDE is supported with machine type q35. Currently,
QEMU will fail startup with machine type q35 with an error like
> Can't create IDE unit 1, bus supports only 1 units
when ide1 or ide3 is configured.

Make sure to keep backwards compat form migration by leaving ide0 and
ide2 fixed. Since starting with ide1 or ide3 never worked, they can be
moved to a controller with a higher ID without issue.

Reported in the community forum:
https://forum.proxmox.com/threads/124615/post-543127
https://forum.proxmox.com/threads/130815/

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---

For PVE 9, we could simplify the mapping to N -> controller=N,unit=0
while version guarding with running QEMU machine version. Might be
slightly nicer, but it'd add an extra conditional, so probably not
worth it.

 PVE/QemuServer.pm             | 11 +++++++++++
 test/cfg2cmd/q35-ide.conf.cmd |  4 ++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 430661a7..aff33728 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -1521,6 +1521,17 @@ sub print_drivedevice_full {
 	my $maxdev = ($drive->{interface} eq 'sata') ? $PVE::QemuServer::Drive::MAX_SATA_DISKS : 2;
 	my $controller = int($drive->{index} / $maxdev);
 	my $unit = $drive->{index} % $maxdev;
+
+	# machine type q35 only supports unit=0 for IDE rather than 2 units. This wasn't handled
+	# correctly before, so e.g. index=2 was mapped to controller=1,unit=0 rather than
+	# controller=2,unit=0. Note that odd indices never worked, as they would be mapped to
+	# unit=1, so to keep backwards compat for migration, it suffices to keep even ones as they
+	# were before. Move odd ones up by 2 where they don't clash.
+	if (PVE::QemuServer::Machine::machine_type_is_q35($conf) && $drive->{interface} eq 'ide') {
+	    $controller += 2 * ($unit % 2);
+	    $unit = 0;
+	}
+
 	my $devicetype = ($drive->{media} && $drive->{media} eq 'cdrom') ? "cd" : "hd";
 
 	$device = "ide-$devicetype";
diff --git a/test/cfg2cmd/q35-ide.conf.cmd b/test/cfg2cmd/q35-ide.conf.cmd
index 7755fdb0..f23d90f3 100644
--- a/test/cfg2cmd/q35-ide.conf.cmd
+++ b/test/cfg2cmd/q35-ide.conf.cmd
@@ -25,11 +25,11 @@
   -drive 'file=/mnt/pve/cifs-store/template/iso/zero.iso,if=none,id=drive-ide0,media=cdrom,aio=threads' \
   -device 'ide-cd,bus=ide.0,unit=0,drive=drive-ide0,id=ide0,bootindex=200' \
   -drive 'file=/mnt/pve/cifs-store/template/iso/one.iso,if=none,id=drive-ide1,media=cdrom,aio=threads' \
-  -device 'ide-cd,bus=ide.0,unit=1,drive=drive-ide1,id=ide1,bootindex=201' \
+  -device 'ide-cd,bus=ide.2,unit=0,drive=drive-ide1,id=ide1,bootindex=201' \
   -drive 'file=/mnt/pve/cifs-store/template/iso/two.iso,if=none,id=drive-ide2,media=cdrom,aio=threads' \
   -device 'ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=202' \
   -drive 'file=/mnt/pve/cifs-store/template/iso/three.iso,if=none,id=drive-ide3,media=cdrom,aio=threads' \
-  -device 'ide-cd,bus=ide.1,unit=1,drive=drive-ide3,id=ide3,bootindex=203' \
+  -device 'ide-cd,bus=ide.3,unit=0,drive=drive-ide3,id=ide3,bootindex=203' \
   -device 'virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5' \
   -drive 'file=/var/lib/vz/images/100/vm-100-disk-2.qcow2,if=none,id=drive-scsi0,format=qcow2,cache=none,aio=io_uring,detect-zeroes=on' \
   -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100' \
-- 
2.39.2