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reset: Add RESET_TYPE_SNAPSHOT_LOAD

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Some devices and machines need to handle the reset before a vmsave
snapshot is loaded differently -- the main user is the handling of
RNG seed information, which does not want to put a new RNG seed into
a ROM blob when we are doing a snapshot load.

Currently this kind of reset handling is supported only for:
 * TYPE_MACHINE reset methods, which take a ShutdownCause argument
 * reset functions registered with qemu_register_reset_nosnapshotload

To allow a three-phase-reset device to also distinguish "snapshot
load" reset from the normal kind, add a new ResetType
RESET_TYPE_SNAPSHOT_LOAD. All our existing reset methods ignore
the reset type, so we don't need to update any device code.

Add the enum type, and make qemu_devices_reset() use the
right reset type for the ShutdownCause it is passed. This
allows us to get rid of the device_reset_reason global we
were using to implement qemu_register_reset_nosnapshotload().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Luc Michel <luc.michel@amd.com>
Message-id: 20240412160809.1260625-7-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2024-04-12 17:08:09 +01:00
parent 41d49ec190
commit 631f46d4ea
4 changed files with 19 additions and 18 deletions
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17
docs/devel/reset.rst
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@ -27,9 +27,7 @@ instantly reset an object, without keeping it in reset state, just call
``resettable_reset()``. These functions take two parameters: a pointer to the
object to reset and a reset type.
Several types of reset will be supported. For now only cold reset is defined;
others may be added later. The Resettable interface handles reset types with an
enum:
The Resettable interface handles reset types with an enum ``ResetType``:
``RESET_TYPE_COLD``
Cold reset is supported by every resettable object. In QEMU, it means we reset
@ -37,6 +35,19 @@ enum:
from what is a real hardware cold reset. It differs from other resets (like
warm or bus resets) which may keep certain parts untouched.
``RESET_TYPE_SNAPSHOT_LOAD``
This is called for a reset which is being done to put the system into a
clean state prior to loading a snapshot. (This corresponds to a reset
with ``SHUTDOWN_CAUSE_SNAPSHOT_LOAD``.) Almost all devices should treat
this the same as ``RESET_TYPE_COLD``. The main exception is devices which
have some non-deterministic state they want to reinitialize to a different
value on each cold reset, such as RNG seed information, and which they
must not reinitialize on a snapshot-load reset.
Devices which implement reset methods must treat any unknown ``ResetType``
as equivalent to ``RESET_TYPE_COLD``; this will reduce the amount of
existing code we need to change if we add more types in future.
Calling ``resettable_reset()`` is equivalent to calling
``resettable_assert_reset()`` then ``resettable_release_reset()``. It is
possible to interleave multiple calls to these three functions. There may