[Qemu-block] [PATCH for-2.6 v2 00/10] fdc: fix 2.88mb floppy diskette support

[John Snow]

Yes, it's been broken for ten years.
No, it's not a CVE.

The problem is that QEMU doesn't have a configuration option for the type
of floppy drive you want. It determines that based on the type of
diskette inserted at boot time.

If you don't insert one, it always chooses a 1.44MB type.

If you want to insert a 2.88MB floppy after boot, you simply cannot.

"Wow, who cares?"

Good question -- Unfortunately, the virtio-win floppy disk images that
Red Hat/fedora ship require a 2.88MB drive, so if you forgot to insert
them at boot, you'd have to change your VM configuration and try again.

For a one-shot operation, that's kind of obnoxious -- it'd be nice to
allow one to just insert the diskette on-demand.

"OK, What are you changing in this decades-old device?"

(1) Add a new property to allow users to specify what kind of drive they
    want without relying on magical guessing behavior.
    Choices are: 120, 144, 288, auto, and none.

    120, 144 and 288 refer to 1.20MB, 1.44MB, and 2.88MB drives.
    auto refers to the auto-detect behavior QEMU currently has.
    none ... hides the drive. You probably don't want to use this.

(2) Add the concept of physical diskette size to QEMU, classifying
    120-style diskettes as fundamentally different from 144 and 288 ones.

(3) Revamp the automatic guessing heuristic to understand that
    2.88MB style drives can accept 1.44MB diskettes.

(4) Change the automatic fallback type for the automatic guessing
    heuristic from 1.44MB to 2.88MB as it is a more diverse drive.

(5) A lot of code cleanup in general.

"Won't this break everything, you madman?"

No: I tested this in MS-DOS 6.22, Fedora 23 and Windows 8.1. All
seemed perfectly happy with 2.88MB drives as the default for 1.44
or 2.88MB floppy diskette images.

If any guests are discovered to be unable to cope with this default,
they are free to choose a 1.44MB drive type at boot, or insert an
appropriate diskette. By and large, this appears to improve the
diskette compatibility for most guests.

________________________________________________________________________________

For convenience, this branch is available at:
https://github.com/jnsnow/qemu.git branch fdc-default
https://github.com/jnsnow/qemu/tree/fdc-default

This version is tagged fdc-default-v2:
https://github.com/jnsnow/qemu/releases/tag/fdc-default-v2

John Snow (10):
  fdc: move pick_geometry
  fdc: refactor pick_geometry
  fdc: add disk field
  fdc: add default drive type option
  fdc: do not call revalidate on eject
  fdc: implement new drive type property
  fdc: add physical disk sizes
  fdc: rework pick_geometry
  qtest/fdc: Support for 2.88MB drives
  fdc: change auto fallback drive to 288

 hw/block/fdc.c               | 317 +++++++++++++++++++++++++++++--------------
 hw/core/qdev-properties.c    |  11 ++
 hw/i386/pc.c                 |  17 +--
 include/hw/block/fdc.h       |   9 +-
 include/hw/qdev-properties.h |   1 +
 qapi/block.json              |  16 +++
 tests/fdc-test.c             |   2 +-
 7 files changed, 255 insertions(+), 118 deletions(-)

-- 
2.4.3