Comment 3 for bug 1697610

In qemuBuildChrChardevStr which builds the "-chardev [..." command it checks the cap QEMU_CAPS_CHARDEV_LOGFILE which we have to assume to be true given the monitor checks I've made.

But in qemuBuildChrArgStr there is an unconditional fail with the same error message.
Just the existance of a logfile definition causes this - so the question is when is qemuBuildChrArgStr be used exactly.

Most code paths insist on the newer qemuBuildChrChardevStr, but there are three that can fall back to qemuBuildChrArgStr if they find no chardev support.
1. qemuBuildMonitorCommandLine - virQEMUCapsGet(qemuCaps, QEMU_CAPS_CHARDEV)
2. qemuBuildSerialCommandLine - virQEMUCapsSupportsChardev(def, qemuCaps, serial)
3. qemuBuildParallelsCommandLine - virQEMUCapsGet(qemuCaps, QEMU_CAPS_CHARDEV)

Since QEMU_CAPS_CHARDEV is always enabled since a long time it might be in virQEMUCapsSupportsChardev related to the serial.

With that known I could already verify that the log= on the pty works just fine.
It is just the log= on the serial that fails.
@admcleod - could that be an artifact of enabling debugging everywhere and not a regression at all?