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

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Message-ID: <20260209144146.GA16995@lst.de>
Date: Mon, 9 Feb 2026 15:41:46 +0100
From: Christoph Hellwig <hch@....de>
To: Dave Chinner <david@...morbit.com>
Cc: Wilfred Mallawa <wilfred.opensource@...il.com>,
	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 Sat, Feb 07, 2026 at 09:27:07AM +1100, Dave Chinner wrote:
> 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.

Except for the pointers it generally is a bug in the structure
defintion, and even for pointers the current consensus is moving
towards encoding them as a u64.  So yeah, this will have to skip
some of the older structures, but for anything newer it the right
thing to do, and will catch issues.