[Bug 1911188] Re: qemu-system-x86_64 prints obscure error message and exits when encountering an empty argument

[Daniel Berrange]

If QEMU receives an argument that isn't an option flag, then it
considers it to be the path to a disk. The block code treats the empty
string as indicating that no backing file should be opened for the
device. This only makes sense for devices that support removable media
(ie CDROM, floppy), hence getting an error message for the ide-hd disk.

So weird as this message might seem, I believe it does ultimately make
sense, and I don't think we can just ignore the empty string without
potentially breaking other things.

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https://bugs.launchpad.net/bugs/1911188

Title:
  qemu-system-x86_64 prints obscure error message and exits when
  encountering an empty argument

Status in QEMU:
  New

Bug description:
  QEMU emulator version 4.2.1 (qemu-4.2.1-1.fc32) on Fedora 32.

  When writing a script to start qemu automatically, I ran into a very
  confusing error message due to a bug in my script and had trouble
  understanding it. I isolated the problem to the following:

  $ qemu-system-x86_64 ""
  qemu-system-x86_64: Initialization of device ide-hd failed: Device needs 
media, but drive is empty

  As you can see, running qemu with an empty argument prints a seemingly
  random and unrelated error message about an ide-hd device, and the
  program immediately exits with code 1. This happens when an empty
  argument appears anywhere in the arguments list, always causing the
  program to immediately die with this error.

  This is a simply baffling message to be encountering when the problem
  is really an empty argument.

  Expected behaviour: Either flatly ignore the empty argument, or at
  most trigger a warning (eg, "warning: saw empty argument"). It should
  not at all prevent the program from running.

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