rust/kernel/devres.rs | 38 +++++++++++++++++++++++++++++++++ rust/kernel/revocable.rs | 12 +++++++++++ samples/rust/rust_driver_pci.rs | 12 +++++------ 3 files changed, 56 insertions(+), 6 deletions(-)
This patch series implements a direct accessor for the data stored within
a Devres container for cases where we can prove that we own a reference
to a Device<Bound> (i.e. a bound device) of the same device that was used
to create the corresponding Devres container.
Usually, when accessing the data stored within a Devres container, it is
not clear whether the data has been revoked already due to the device
being unbound and, hence, we have to try whether the access is possible
and subsequently keep holding the RCU read lock for the duration of the
access.
However, when we can prove that we hold a reference to Device<Bound>
matching the device the Devres container has been created with, we can
guarantee that the device is not unbound for the duration of the
lifetime of the Device<Bound> reference and, hence, it is not possible
for the data within the Devres container to be revoked.
Therefore, in this case, we can bypass the atomic check and the RCU read
lock, which is a great optimization and simplification for drivers.
The patches of this series are also available in [1].
[1] https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/devres
Changes in v2:
- Revocable::access(): remvoe explicit lifetimes; don't refer to 'a in
the safety requirement
- Devres::access()
- rename Devres::access_with() to Devres::access()
- add missing '```' at the end of the example
- remove 's lifetime
- add # Errors section
Danilo Krummrich (3):
rust: revocable: implement Revocable::access()
rust: devres: implement Devres::access_with()
samples: rust: pci: take advantage of Devres::access_with()
rust/kernel/devres.rs | 38 +++++++++++++++++++++++++++++++++
rust/kernel/revocable.rs | 12 +++++++++++
samples/rust/rust_driver_pci.rs | 12 +++++------
3 files changed, 56 insertions(+), 6 deletions(-)
base-commit: 3be746ebc1e6e32f499a65afe405df9030153a63
--
2.49.0
On Mon, Apr 28, 2025 at 04:00:26PM +0200, Danilo Krummrich wrote: > This patch series implements a direct accessor for the data stored within > a Devres container for cases where we can prove that we own a reference > to a Device<Bound> (i.e. a bound device) of the same device that was used > to create the corresponding Devres container. Applied to nova-next, thanks!
On Mon Apr 28, 2025 at 11:00 PM JST, Danilo Krummrich wrote: > This patch series implements a direct accessor for the data stored within > a Devres container for cases where we can prove that we own a reference > to a Device<Bound> (i.e. a bound device) of the same device that was used > to create the corresponding Devres container. > > Usually, when accessing the data stored within a Devres container, it is > not clear whether the data has been revoked already due to the device > being unbound and, hence, we have to try whether the access is possible > and subsequently keep holding the RCU read lock for the duration of the > access. > > However, when we can prove that we hold a reference to Device<Bound> > matching the device the Devres container has been created with, we can > guarantee that the device is not unbound for the duration of the > lifetime of the Device<Bound> reference and, hence, it is not possible > for the data within the Devres container to be revoked. > > Therefore, in this case, we can bypass the atomic check and the RCU read > lock, which is a great optimization and simplification for drivers. Thanks, this removes one of my pain points with the way revocable resources were accessed and will allow to write drivers in a much more natural way. FWIW, the series Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
> On Apr 29, 2025, at 10:46 PM, Alexandre Courbot <acourbot@nvidia.com> wrote: > > On Mon Apr 28, 2025 at 11:00 PM JST, Danilo Krummrich wrote: >> This patch series implements a direct accessor for the data stored within >> a Devres container for cases where we can prove that we own a reference >> to a Device<Bound> (i.e. a bound device) of the same device that was used >> to create the corresponding Devres container. >> >> Usually, when accessing the data stored within a Devres container, it is >> not clear whether the data has been revoked already due to the device >> being unbound and, hence, we have to try whether the access is possible >> and subsequently keep holding the RCU read lock for the duration of the >> access. >> >> However, when we can prove that we hold a reference to Device<Bound> >> matching the device the Devres container has been created with, we can >> guarantee that the device is not unbound for the duration of the >> lifetime of the Device<Bound> reference and, hence, it is not possible >> for the data within the Devres container to be revoked. >> >> Therefore, in this case, we can bypass the atomic check and the RCU read >> lock, which is a great optimization and simplification for drivers. > > Thanks, this removes one of my pain points with the way revocable > resources were accessed and will allow to write drivers in a much more > natural way. > > FWIW, the series > > Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Nice, I like it. Quite a readability improvement too on the caller side! Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com> Thanks.
On Mon, Apr 28, 2025 at 04:00:26PM +0200, Danilo Krummrich wrote: > This patch series implements a direct accessor for the data stored within > a Devres container for cases where we can prove that we own a reference > to a Device<Bound> (i.e. a bound device) of the same device that was used > to create the corresponding Devres container. > > Usually, when accessing the data stored within a Devres container, it is > not clear whether the data has been revoked already due to the device > being unbound and, hence, we have to try whether the access is possible > and subsequently keep holding the RCU read lock for the duration of the > access. > > However, when we can prove that we hold a reference to Device<Bound> > matching the device the Devres container has been created with, we can > guarantee that the device is not unbound for the duration of the > lifetime of the Device<Bound> reference and, hence, it is not possible > for the data within the Devres container to be revoked. > > Therefore, in this case, we can bypass the atomic check and the RCU read > lock, which is a great optimization and simplification for drivers. > Acked-by: Boqun Feng <boqun.feng@gmail.com> You would need to, however, change the titles for patch #2 and #3 because there is no `Devres::access_with()` any more. Regards, Boqun > The patches of this series are also available in [1]. > > [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/devres > > Changes in v2: > - Revocable::access(): remvoe explicit lifetimes; don't refer to 'a in > the safety requirement > - Devres::access() > - rename Devres::access_with() to Devres::access() > - add missing '```' at the end of the example > - remove 's lifetime > - add # Errors section > > Danilo Krummrich (3): > rust: revocable: implement Revocable::access() > rust: devres: implement Devres::access_with() > samples: rust: pci: take advantage of Devres::access_with() > > rust/kernel/devres.rs | 38 +++++++++++++++++++++++++++++++++ > rust/kernel/revocable.rs | 12 +++++++++++ > samples/rust/rust_driver_pci.rs | 12 +++++------ > 3 files changed, 56 insertions(+), 6 deletions(-) > > > base-commit: 3be746ebc1e6e32f499a65afe405df9030153a63 > -- > 2.49.0 >
On Mon, Apr 28, 2025 at 10:39:17AM -0700, Boqun Feng wrote: > On Mon, Apr 28, 2025 at 04:00:26PM +0200, Danilo Krummrich wrote: > > This patch series implements a direct accessor for the data stored within > > a Devres container for cases where we can prove that we own a reference > > to a Device<Bound> (i.e. a bound device) of the same device that was used > > to create the corresponding Devres container. > > > > Usually, when accessing the data stored within a Devres container, it is > > not clear whether the data has been revoked already due to the device > > being unbound and, hence, we have to try whether the access is possible > > and subsequently keep holding the RCU read lock for the duration of the > > access. > > > > However, when we can prove that we hold a reference to Device<Bound> > > matching the device the Devres container has been created with, we can > > guarantee that the device is not unbound for the duration of the > > lifetime of the Device<Bound> reference and, hence, it is not possible > > for the data within the Devres container to be revoked. > > > > Therefore, in this case, we can bypass the atomic check and the RCU read > > lock, which is a great optimization and simplification for drivers. > > > > Acked-by: Boqun Feng <boqun.feng@gmail.com> > > You would need to, however, change the titles for patch #2 and #3 > because there is no `Devres::access_with()` any more. Thanks, good catch! Unless we need a v3 for something else, I'll fix it when I apply the series.
© 2016 - 2025 Red Hat, Inc.