This adds a function to shut down all block exports, and another one to
shut down the block exports of a single type. The latter is used for now
when stopping the NBD server. As soon as we implement support for
multiple NBD servers, we'll need a per-server list of exports and it
will be replaced by a function using that.

As a side effect, the BlockExport layer has a list tracking all existing
exports now. closed_exports loses its only user and can go away.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-18-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Instead of letting the driver allocate and return the BlockExport
object, allocate it already in blk_exp_add() and pass it. This allows us
to initialise the generic part before calling into the driver so that
the driver can just use these values instead of having to parse the
options a second time.

For symmetry, move freeing the BlockExport to blk_exp_unref().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-17-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Every block export needs a block node to export, so add a 'node-name'
option to BlockExportOptions and remove the replaced option 'device'
from BlockExportOptionsNbd.

To maintain compatibility in nbd-server-add, BlockExportOptionsNbd needs
to be wrapped by a new type NbdServerAddOptions that adds 'device' back
because nbd-server-add doesn't use the BlockExportOptions base type at
all (so even without changing it to a 'node-name' option in
block-export-add, this compatibility code would be necessary).

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-16-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-15-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Having a refcount makes sense for all types of block exports. It is also
a prerequisite for keeping a list of all exports at the BlockExport
level.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-14-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Closing export is somewhat convoluted because nbd_export_close() and
nbd_export_put() call each other and the ways they actually end up being
nested is not necessarily obvious.

However, it is not really necessary to call nbd_export_close() from
nbd_export_put() when putting the last reference because it only does
three things:

1. Close all clients. We're going to refcount 0 and all clients hold a
   reference, so we know there is no active client any more.

2. Close the user reference (represented by exp->name being non-NULL).
   The same argument applies: If the export were still named, we would
   still have a reference.

3. Freeing exp->description. This is really cleanup work to be done when
   the export is finally freed. There is no reason to already clear it
   while clients are still in the process of shutting down.

So after moving the cleanup of exp->description, the code can be
simplified so that only nbd_export_close() calls nbd_export_put(), but
never the other way around.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-13-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

With this change, NBD exports are now only created through the
BlockExport interface. This allows us finally to move things from the
NBD layer to the BlockExport layer if they make sense for other export
types, too.

blk_exp_add() returns only a weak reference, so the explicit
nbd_export_put() goes away.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-12-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

The export close callback is unused by the built-in NBD server. qemu-nbd
uses it only during shutdown to wait for the unrefed export to actually
go away. It can just use nbd_export_close_all() instead and do without
the callback.

This removes the close callback from nbd_export_new() and makes both
callers of it more similar.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-11-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

qemu-nbd allows use of writethrough cache modes, which mean that write
requests made through NBD will cause a flush before they complete.
Expose the same functionality in block-export-add.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-10-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

This is a QMP equivalent of qemu-nbd's --shared option, limiting the
maximum number of clients that can attach at the same time.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-9-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

nbd-server-add tries to be convenient and adds two questionable
features that we don't want to share in block-export-add, even for NBD
exports:

1. When requesting a writable export of a read-only device, the export
   is silently downgraded to read-only. This should be an error in the
   context of block-export-add.

2. When using a BlockBackend name, unplugging the device from the guest
   will automatically stop the NBD server, too. This may sometimes be
   what you want, but it could also be very surprising. Let's keep
   things explicit with block-export-add. If the user wants to stop the
   export, they should tell us so.

Move these things into the nbd-server-add QMP command handler so that
they apply only there.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-8-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Instead of implementing qemu-nbd --offset in the NBD code, just put a
raw block node with the requested offset on top of the user image and
rely on that doing the job.

This does not only simplify the nbd_export_new() interface and bring it
closer to the set of options that the nbd-server-add QMP command offers,
but in fact it also eliminates a potential source for bugs in the NBD
code which previously had to add the offset manually in all relevant
places.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-7-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

No reason to duplicate the functionality locally, we can now just reuse
the QMP command block-export-add for --export.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-6-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

We want to have a common set of commands for all types of block exports.
Currently, this is only NBD, but we're going to add more types.

This patch adds the basic BlockExport and BlockExportDriver structs and
a QMP command block-export-add that creates a new export based on the
given BlockExportOptions.

qmp_nbd_server_add() becomes a wrapper around qmp_block_export_add().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-5-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

The name BlockExport will be used for the struct containing the runtime
state of block exports, so change the name of export creation options.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-4-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Move all block export related types and commands from block-core to the
new QAPI module block-export.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-3-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200924152717.287415-2-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

help_oneline is declared and starts as:

  static void help_oneline(const char *cmd, const cmdinfo_t *ct)
  {
      if (cmd) {
          printf("%s ", cmd);
      } else {
          printf("%s ", ct->name);
          if (ct->altname) {
              printf("(or %s) ", ct->altname);
          }
      }

However, there are only two routes to help_oneline being called:

   help_f -> help_all -> help_oneline(ct->name, ct)

   help_f -> help_onecmd(argv[1], ct)

In the first case, 'cmd' and 'ct->name' are the same thing,
so it's impossible for the if (cmd) to be false and then validly
print ct->name - this is upsetting gcc
( https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96739

 )

In the second case, cmd is argv[1] and we know we've got argv[1]
so again (cmd) is non-NULL.

Simplify help_oneline by just printing cmd.
(Also strengthen argc check just to be pedantic)

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20200824102914.105619-1-dgilbert@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

This filter was added back in 2017 for QEMU 2.11 but it was never
properly documented, so let's explain how it works and add a couple of
examples.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20200921173016.27935-1-berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

macOS is shipped with a very old version of the bash (3.2), which
is currently not suitable for running the iotests anymore (e.g.
it is missing support for "readarray" which is used in the file
tests/qemu-iotests/common.filter). Add a check to skip the iotests
in this case - if someone still wants to run the iotests on macOS,
they can install a newer version from homebrew, for example.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20200918153514.330705-1-thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Use self-explicit NANOSECONDS_PER_SECOND definition instead
of magic value.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200921110145.520944-1-philmd@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Python testing updates:

  - drop python 3.5 test from travis
  - replace Debian 9 containers with 10
  - increase cross build timeout
  - bump minimum python version in configure
  - move user plugins tests to gitlab
  - split deprecated builds into build and test

# gpg: Signature made Fri 02 Oct 2020 12:34:36 BST
# gpg:                using RSA key 6685AE99E75167BCAFC8DF35FBD0DB095A9E2A44
# gpg: Good signature from "Alex Bennée (Master Work Key) <alex.bennee@linaro.org>" [full]
# Primary key fingerprint: 6685 AE99 E751 67BC AFC8  DF35 FBD0 DB09 5A9E 2A44

* remotes/stsquad/tags/pull-testing-and-python-021020-1:
  gitlab: split deprecated job into build/check stages
  gitlab: move linux-user plugins test across to gitlab
  configure: Bump the minimum required Python version to 3.6
  gitlab-ci: Increase the timeout for the cross-compiler builds
  tests/docker: Remove old Debian 9 containers
  shippable.yml: Remove the Debian9-based MinGW cross-compiler tests
  tests/docker: Update the tricore container to debian 10
  gitlab-ci: Remove the Debian9-based containers and containers-layer3
  tests/docker: Use Fedora containers for MinGW cross-builds in the gitlab-CI
  travis.yml: Drop the Python 3.5 build
  travis.yml: Drop the superfluous Python 3.6 build
  travis.yml: Update Travis to use Bionic and Focal instead of Xenial
  travis.yml: Drop the default softmmu builds
  migration: Silence compiler warning in global_state_store_running()

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

While the job is pretty fast for only a few targets we still want to
catch breakage of the build. By splitting the test step we can
allow_failures for that while still ensuring we don't miss the build
breaking.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20201002091538.3017-1-alex.bennee@linaro.org>

Even with the recent split moving beefier plugins into contrib and
dropping them from the check-tcg tests we are still hitting time
limits. This possibly points to a slow down of --debug-tcg but seeing
as we are migrating stuff to gitlab we might as well move there and
bump the timeout.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20201002103223.24022-1-alex.bennee@linaro.org>

All our supported build platforms have Python 3.6 or newer nowadays, and
there are some useful features in Python 3.6 which are not available in
3.5 yet (e.g. the type hint annotations which will allow us to statically
type the QAPI parser), so let's bump the minimum Python version to 3.6 now.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200923162908.95372-1-thuth@redhat.com>
Message-Id: <20200925154027.12672-16-alex.bennee@linaro.org>

Some of the cross-compiler builds (the mips build and the win64 build
for example) are quite slow and sometimes hit the 1h time limit.
Increase the limit a little bit to make sure that we do not get failures
in the CI runs just because of some few minutes.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200921174320.46062-7-thuth@redhat.com>
Message-Id: <20200925154027.12672-15-alex.bennee@linaro.org>

We do not support Debian 9 in QEMU anymore, and the Debian 9 containers
are now no longer used in the gitlab-CI. Time to remove them.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200921174320.46062-6-thuth@redhat.com>
Message-Id: <20200925154027.12672-14-alex.bennee@linaro.org>

We're not supporting Debian 9 anymore, and we are now testing
MinGW cross-compiler builds in the gitlab-CI, too, so we do not
really need these jobs in the shippable.yml anymore.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200921174320.46062-5-thuth@redhat.com>
Message-Id: <20200925154027.12672-13-alex.bennee@linaro.org>

We do not support Debian 9 anymore, thus update the Tricore container
to Debian 10 now.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200921174320.46062-4-thuth@redhat.com>
Message-Id: <20200925154027.12672-12-alex.bennee@linaro.org>

According to our support policy, Debian 9 is not supported by the
QEMU project anymore. Since we now switched the MinGW cross-compiler
builds to Fedora, we do not need these Debian9-based containers
in the gitlab-CI anymore, and can now also get rid of the "layer3"
container build stage this way.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200921174320.46062-3-thuth@redhat.com>
Message-Id: <20200925154027.12672-11-alex.bennee@linaro.org>

According to our support policy, we do not support Debian 9 in QEMU
anymore, and we only support building the Windows binaries with a
very recent version of the MinGW toolchain. So we should not test
the MinGW cross-compilation with Debian 9 anymore, but switch to
something newer like Fedora. To do this, we need a separate Fedora
container for each build that provides the QEMU_CONFIGURE_OPTS
environment variable.
Unfortunately, the MinGW 64-bit compiler seems to be a little bit
slow, so we also have to disable some features like "capstone" in the
build here to make sure that the CI pipelines still finish within a
reasonable amount of time.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200921174320.46062-2-thuth@redhat.com>
Message-Id: <20200925154027.12672-10-alex.bennee@linaro.org>

We are soon going to remove the support for Python 3.5. So remove
the CI job now.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200922070441.48844-1-thuth@redhat.com>
Message-Id: <20200925154027.12672-9-alex.bennee@linaro.org>

Python 3.6 is already the default Python in the jobs that are based
on Ubuntu Bionic, so it does not make much sense to test this again
separately.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200918103430.297167-7-thuth@redhat.com>
Message-Id: <20200925154027.12672-8-alex.bennee@linaro.org>

According to our support policy, we do not support Xenial anymore.
Time to switch the bigger parts of the builds to Focal instead.
Some few jobs have to be updated to Bionic instead, since they are
currently still failing on Focal otherwise. Also "--disable-pie" is
causing linker problems with newer versions of Ubuntu ... so remove
that switch from the jobs now (we still test it in a gitlab CI job,
so we don't lose much test coverage here).

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20200918103430.297167-6-thuth@redhat.com>
Message-Id: <20200925154027.12672-7-alex.bennee@linaro.org>

The total runtime of all Travis jobs is very long and we are testing
all softmmu targets in the gitlab-CI already - so we can speed up the
Travis testing a little bit by not testing the softmmu targets here
anymore.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200918103430.297167-5-thuth@redhat.com>
Message-Id: <20200925154027.12672-6-alex.bennee@linaro.org>

GCC 9.3.0 on Ubuntu complains:

In file included from /usr/include/string.h:495,
                 from /home/travis/build/huth/qemu/include/qemu/osdep.h:87,
                 from ../migration/global_state.c:13:
In function ‘strncpy’,
    inlined from ‘global_state_store_running’ at ../migration/global_state.c:47:5:
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error:
 ‘__builtin_strncpy’ specified bound 100 equals destination size [-Werror=stringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

... but we apparently really want to do a strncpy here - the size is already
checked with the assert() statement right in front of it. To silence the
warning, simply replace it with our strpadcpy() function.

Suggested-by: Philippe Mathieu-Daudé <philmd@redhat.com> (two years ago)
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200918103430.297167-4-thuth@redhat.com>
Message-Id: <20200925154027.12672-5-alex.bennee@linaro.org>

Pull request

# gpg: Signature made Thu 01 Oct 2020 18:41:05 BST
# gpg:                using RSA key F9B7ABDBBCACDF95BE76CBD07DEF8106AAFC390E
# gpg: Good signature from "John Snow (John Huston) <jsnow@redhat.com>" [full]
# Primary key fingerprint: FAEB 9711 A12C F475 812F  18F2 88A9 064D 1835 61EB
#      Subkey fingerprint: F9B7 ABDB BCAC DF95 BE76  CBD0 7DEF 8106 AAFC 390E

* remotes/jsnow-gitlab/tags/ide-pull-request:
  ide: cancel pending callbacks on SRST
  ide: clear interrupt on command write
  ide: remove magic constants from the device register
  ide: reorder set/get sector functions
  ide: model HOB correctly
  ide: don't tamper with the device register
  ide: rename cmd_write to ctrl_write
  hw/ide/ahci: Do not dma_memory_unmap(NULL)
  MAINTAINERS: Update my git address

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

The SRST implementation did not keep up with the rest of IDE; it is
possible to perform a weak reset on an IDE device to remove the BSY/DRQ
bits, and then issue writes to the control/device registers which can
cause chaos with the state machine.

Fix that by actually performing a real reset.

Reported-by: Alexander Bulekov <alxndr@bu.edu>
Fixes: https://bugs.launchpad.net/qemu/+bug/1878253
Fixes: https://bugs.launchpad.net/qemu/+bug/1887303
Fixes: https://bugs.launchpad.net/qemu/+bug/1887309


Signed-off-by: John Snow <jsnow@redhat.com>

Not known to fix any bug, but I couldn't help but notice that ATA
specifies that writing to this register should clear an interrupt.

ATA7: Section 5.3.3 (Command register - Effect)
ATA6: Section 7.4.4 (Command register - Effect)
ATA5: Section 7.4.4 (Command register - Effect)
ATA4: Section 7.4.4 (Command register - Effect)
ATA3: Section 5.2.2 (Command register)

Other editions: try searching for the phrase "Writing this register".

Signed-off-by: John Snow <jsnow@redhat.com>

(In QEMU, we call this the "select" register.)

My memory isn't good enough to memorize what these magic runes
do. Label them to prevent mixups from happening in the future.

Side note: I assume it's safe to always set 0xA0 even though ATA2 claims
these bits are reserved, because ATA3 immediately reinstated that these
bits should be always on. ATA4 and subsequent specs only claim that the
fields are obsolete, so I assume it's safe to leave these set and that
it should work with the widest array of guests.

Signed-off-by: John Snow <jsnow@redhat.com>