linux-kernel - Re: [PATCH] xfs: add static size checks for structures in xfs

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Message-ID: <aYZquyDjPqZIcKe4@dread.disaster.area>
Date: Sat, 7 Feb 2026 09:27:07 +1100
From: Dave Chinner <david@...morbit.com>
To: Wilfred Mallawa <wilfred.opensource@...il.com>
Cc: Carlos Maiolino <cem@...nel.org>,
	"Darrick J . Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
	Wilfred Mallawa <wilfred.mallawa@....com>
Subject: Re: [PATCH] xfs: add static size checks for structures in xfs_fs.h

On Fri, Feb 06, 2026 at 01:05:58PM +1000, Wilfred Mallawa wrote:
> From: Wilfred Mallawa <wilfred.mallawa@....com>
> 
> This patch adds static size checks for the structures in
> libxfs/xfs_fs.h. The structures with architecture dependent size for
> fields are ommited from this patch (such as xfs_bstat which depends on
> __kernel_long_t).

There's more than that.

Different architectures will have different padding, alignment and
holes for the same structure (e.g. 32 bit vs 64 bit) resulting in
different sizes for the same structure across different platforms.

This is not actually a bug in the UAPI - as long as the
architecture's userspace and the kernel are using the same structure
layout, variations in structure size and layout between architectures
don't matter.

IOWs, if these structures checks are sized to pass on x86_64, I'd
expect this change to result in build failures on various 32 bit
platforms....

-Dave.
-- 
Dave Chinner
david@...morbit.com