From: Asahi Lina <lina@asahilina.net>
To: "Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Matthew Wilcox" <willy@infradead.org>
Cc: Martin Rodriguez Reboredo <yakoyoku@gmail.com>,
Neal Gompa <neal@gompa.dev>,
linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org,
asahi@lists.linux.dev
Subject: Re: [PATCH v2] rust: xarray: Add an abstraction for XArray
Date: Fri, 24 Mar 2023 01:29:53 +0900 [thread overview]
Message-ID: <e5e24cec-f4b5-b641-c860-c157663c1ff8@asahilina.net> (raw)
In-Reply-To: <20230224-rust-xarray-v2-1-4eeb0134944c@asahilina.net>
Why do I always notice mistakes after sending the patch... this is
missing the comment I intended to add because I edited the file in the
wrong git checkout. Sorry!
The intended comment is below, I'll roll it into v3 when I make the
Error API change.
On 24/03/2023 01.23, Asahi Lina wrote:
> The XArray is an abstract data type which behaves like a very large
> array of pointers. Add a Rust abstraction for this data type.
>
> The initial implementation uses explicit locking on get operations and
> returns a guard which blocks mutation, ensuring that the referenced
> object remains alive. To avoid excessive serialization, users are
> expected to use an inner type that can be efficiently cloned (such as
> Arc<T>), and eagerly clone and drop the guard to unblock other users
> after a lookup.
>
> Future variants may support using RCU instead to avoid mutex locking.
>
> This abstraction also introduces a reservation mechanism, which can be
> used by alloc-capable XArrays to reserve a free slot without immediately
> filling it, and then do so at a later time. If the reservation is
> dropped without being filled, the slot is freed again for other users,
> which eliminates the need for explicit cleanup code.
>
> Signed-off-by: Asahi Lina <lina@asahilina.net>
[...]
> +impl<T: ForeignOwnable> Drop for XArray<T> {
> + fn drop(&mut self) {
> + // SAFETY: `self.xa` is valid by the type invariant, and as we have the only reference to
> + // the `XArray` we can safely iterate its contents and drop everything.
> + unsafe {
> + let mut index: core::ffi::c_ulong = 0;
> + let mut entry = bindings::xa_find(
> + self.xa.get(),
> + &mut index,
> + core::ffi::c_ulong::MAX,
> + bindings::BINDINGS_XA_PRESENT,
> + );
> + while !entry.is_null() {
> + T::from_foreign(entry);
> + entry = bindings::xa_find_after(
> + self.xa.get(),
> + &mut index,
> + core::ffi::c_ulong::MAX,
> + bindings::BINDINGS_XA_PRESENT,
> + );
> + }
> +
Add for v3:
> + // Locked locks are not safe to drop. Normally we would want to try_lock()/unlock() here
> + // for safety or something similar, but in this case xa_destroy() is guaranteed to
> + // acquire the lock anyway. This will deadlock if a lock guard was improperly dropped,
> + // but that is not UB, so it's sufficient for soundness purposes.
> + bindings::xa_destroy(self.xa.get());
> + }
> + }
> +}
> +
> +// SAFETY: XArray is thread-safe and all mutation operations are internally locked.
> +unsafe impl<T: Send + ForeignOwnable> Send for XArray<T> {}
> +unsafe impl<T: Sync + ForeignOwnable> Sync for XArray<T> {}
>
> ---
> base-commit: 3ef2e9730ba4bb914dd8654ae34aef3f486c8c58
> change-id: 20230224-rust-xarray-f503f9e5455e
>
> Thank you,
> ~~ Lina
>
>
~~ Lina
prev parent reply other threads:[~2023-03-23 16:30 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-23 16:23 [PATCH v2] rust: xarray: Add an abstraction for XArray Asahi Lina
2023-03-23 16:29 ` Asahi Lina [this message]
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