rust: add RevocableMutex.
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This is a mutex where access to its contents can be revoked at runtime. This is different from `Revocable` in a few ways: 1. The caller may sleep while holding a guard. 2. Accessors are all serialised. 3. Accessing is not as cheap (because it involves acquiring the mutex). 4. The size of the object is larger (because it involves a mutex + flag). An example of where this a good fit to be used in device state that holds registrations to other subsystems, for example, the PL061 driver registers with the gpio subsystem; the registration is only used on `probe` and is revoked on `remove`. Signed-off-by: Wedson Almeida Filho <[email protected]>
This was referenced Nov 26, 2021
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bjorn3
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Nov 27, 2021
| /// | ||
| /// Revocation and dropping happens after ongoing accessors complete. | ||
| pub fn revoke(&self) { | ||
| let mut inner = self.inner.lock(); |
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Would it make sense to have .revoke() set an atomic flag that signals revocation and only drop the inner value if the mutex isn't locke and otherwise let the mutex guard drop it when dropping?
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Upon return from revoke, we want to ensure that the inner value has been dropped.
This is because the scenario where this is used at the moment is when remove is called on a device: we want all io resources and registrations to be dropped before returning (to ensure that they won't be used again).
If we were to do as you suggest, we could get into a situation where, for example, a GPIO is still exposed to userspace even though the device has already been removed.
bjorn3
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Nov 27, 2021
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This is a mutex where access to its contents can be revoked at runtime.
This is different from
Revocablein a few ways:flag).
An example of where this a good fit to be used in device state that
holds registrations to other subsystems, for example, the PL061 driver
registers with the gpio subsystem; the registration is only used on
probeand is revoked onremove.Signed-off-by: Wedson Almeida Filho [email protected]