linux-kernel - Re: [PATCH] pci: provide pci_free_irq_vectors() stub when CONFIG

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Message-ID: <5521e98b-e12d-4af1-adcd-2dc56863f90b@gmail.com>
Date: Mon, 22 Dec 2025 08:02:44 +0100
From: Dirk Behme <dirk.behme@...il.com>
To: Liang Jie <buaajxlj@....com>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 Joel Fernandes <joelagnelf@...dia.com>,
 "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:RUST:Keyword:b(?i:rust)b" <rust-for-linux@...r.kernel.org>,
 "open list:CLANG/LLVM BUILD SUPPORT:Keyword:b(?i:clang|llvm)b"
 <llvm@...ts.linux.dev>
Cc: liangjie@...iang.com, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] pci: provide pci_free_irq_vectors() stub when CONFIG_PCI
 is disabled

On 22.12.25 04:44, Liang Jie wrote:
> From: Liang Jie <liangjie@...iang.com>
> 
> When building with CONFIG_PCI=n, clang reports:
> 
>   In file included from rust/helpers/helpers.c:40:
>   rust/helpers/pci.c:36:2: error: call to undeclared function 'pci_free_irq_vectors';
>   ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>           pci_free_irq_vectors(dev);
>           ^
>   rust/helpers/pci.c:36:2: note: did you mean 'pci_alloc_irq_vectors'?
>   include/linux/pci.h:2161:1: note: 'pci_alloc_irq_vectors' declared here
>   pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
>   ^
>   1 error generated.
> 
> The root cause is that include/linux/pci.h provides inline stubs for
> pci_alloc_irq_vectors() in the CONFIG_PCI=n fallback, but does not provide
> any declaration for pci_free_irq_vectors(). As a result, callers that invoke
> pci_free_irq_vectors() under CONFIG_PCI=n (e.g. Rust PCI helpers) hit an
> implicit function declaration error with clang.
> 
> Fix this by adding a no-op pci_free_irq_vectors() stub to the CONFIG_PCI=n
> fallback section of include/linux/pci.h, keeping the alloc/free API pair
> consistent and avoiding implicit declaration build failures.
> 
> Fixes: 473b9f331718 ("rust: pci: fix build failure when CONFIG_PCI_MSI is disabled")
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202512220740.4Kexm4dW-lkp@intel.com/
> Signed-off-by: Liang Jie <liangjie@...iang.com>
> ---
>  include/linux/pci.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 864775651c6f..b5cc0c2b9906 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2210,6 +2210,10 @@ pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
>  {
>  	return -ENOSPC;
>  }
> +
> +static inline void pci_free_irq_vectors(struct pci_dev *dev)
> +{
> +}
>  #endif /* CONFIG_PCI */
>  
>  /* Include architecture-dependent settings and functions */

We have this from Boqun already

https://lore.kernel.org/rust-for-linux/20251215025444.65544-1-boqun.feng@gmail.com/

?

Dirk