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[2003:df:bf22:3c00:1c42:64e:ef2a:93cd]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42f7cc090bdsm18354202f8f.19.2025.12.06.23.12.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 06 Dec 2025 23:12:13 -0800 (PST) Message-ID: Date: Sun, 7 Dec 2025 08:12:10 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 1/7] rust: pci: expose sriov_get_totalvfs() helper To: Zhi Wang , rust-for-linux@vger.kernel.org, linux-pci@vger.kernel.org, nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: airlied@gmail.com, dakr@kernel.org, aliceryhl@google.com, bhelgaas@google.com, kwilczynski@kernel.org, ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, tmgross@umich.edu, markus.probst@posteo.de, helgaas@kernel.org, cjia@nvidia.com, alex@shazbot.org, smitra@nvidia.com, ankita@nvidia.com, aniketa@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, acourbot@nvidia.com, joelagnelf@nvidia.com, jhubbard@nvidia.com, zhiwang@kernel.org References: <20251206124208.305963-1-zhiw@nvidia.com> <20251206124208.305963-2-zhiw@nvidia.com> Content-Language: de-AT-frami, en-US From: Dirk Behme In-Reply-To: <20251206124208.305963-2-zhiw@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 06.12.25 13:42, Zhi Wang wrote: > Add a wrapper for the `pci_sriov_get_totalvfs()` helper, allowing drivers > to query the number of total SR-IOV virtual functions a PCI device > supports. > > This is useful for components that need to conditionally enable features > based on SR-IOV capability. > > Signed-off-by: Zhi Wang > --- > rust/kernel/pci.rs | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs > index 7fcc5f6022c1..9a82e83dfd30 100644 > --- a/rust/kernel/pci.rs > +++ b/rust/kernel/pci.rs > @@ -514,6 +514,18 @@ pub fn pci_class(&self) -> Class { > // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`. > Class::from_raw(unsafe { (*self.as_raw()).class }) > } > + > + /// Returns total number of VFs, or `Err(ENODEV)` if none available. > + pub fn sriov_get_totalvfs(&self) -> Result { > + // SAFETY: `self.as_raw()` is a valid pointer to a `struct pci_dev`. > + let vfs = unsafe { bindings::pci_sriov_get_totalvfs(self.as_raw()) }; > + > + if vfs != 0 { > + Ok(vfs) > + } else { > + Err(ENODEV) > + } In the thread [1] there was some discussion about the `if {} else {}` "style". From that discussion I "distilled" 6 options [2] which I liked for having an overview :) Of course not all of these applied there (const), neither will they here. And all have pros and cons. I think in the end option #4 was selected. What's about to do something similar here (and in the 2/7 patch as well)? if vfs == 0 { return Err(ENODEV); } Ok(vfs) Dirk [1] https://lore.kernel.org/rust-for-linux/CANiq72kiscT5euAUjcSzvxMzM9Hdj8aQGeUN_pVF-vHf3DhBuQ@mail.gmail.com/ [2] Options distilled from the thread [1]: 1. if let Some(sum) = addr.checked_add(PAGE_SIZE - 1) { return Some(sum & PAGE_MASK); } None 2. addr.checked_add(PAGE_SIZE - 1).map(|sum| sum & PAGE_MASK) 3. if let Some(sum) = addr.checked_add(PAGE_SIZE - 1) { Some(sum & PAGE_MASK); } else { None } 4. let Some(sum) = addr.checked_add(PAGE_SIZE - 1) else { return None; }; Some(sum & PAGE_MASK) 5. match addr.checked_add(PAGE_SIZE - 1) { Some(v) => Some(v & PAGE_MASK), None => None, } 6. Some(addr.checked_add(PAGE_SIZE - 1)? & PAGE_MASK)