The Device ops
Caution: This page may contain information that is specific to the legacy version of the driver framework (DFv1).
Please refer to the [header comments][device] for descriptions of the methods.
Hook ordering guarantees
The hooks that a driver implements will be invoked by other drivers and by the runtime. These invocations in some occasions may occur in parallel with invocations of other or even the same hook. This section will describe the ordering properties that you may rely on.
Terminology
This section uses the terms unsequenced, indeterminately sequenced, and sequenced before as they are used in the C++ execution model.
Driver Initialization
The [zx_driver_ops_t][driver] init hook will execute completely before any other hooks for that driver.
Driver Teardown
The [zx_driver_ops_t][driver] release hook will begin execution only after all devices created by this driver have been released.
Driver Bind
If tests are enabled, the [zx_driver_ops_t][driver] bind hook will begin execution only after the run_unit_tests hook.
Device Lifecycle
The device lifecycle begins when some driver successfully invokes device_add(). This may occur on any thread. No [zx_device_ops_t][device] hooks will run before the device's lifecycle has begun or after it has ended.
The device lifecycle ends when the device's release hook has begun executing.
The [zx_device_ops_t][device] hooks are unsequenced with respect to each other unless otherwise specified.
Note: This means that any code that occurs after a call to device_add(), even in bind hooks, is unsequenced with respect to the end of the created device's lifecycle.
Device Connection Lifecycle
A device connection lifecycle begins when the [zx_device_ops_t][device] open hook begins executing. None of the [zx_device_ops_t][device] read/write/message/close hooks will be invoked if the number of alive device connections is 0.
A device connection lifecycle ends when the [zx_device_ops_t][device] close hook begins executing. Any execution of read/write/message hooks is sequenced before this.
Since the read/write/message hooks only execute on the driver host's main thread, they will never be executed concurrently but the processing of outstanding requests from different connections will be indeterminately sequenced.
Misc Device APIs
The [zx_device_ops_t][device] get_size and get_protocol hooks are unsequenced with respect to all hooks (including concurrent invocations of themselves). The one exception to this is that they are sequenced before the release hook.