linux-kernel - Re: [PATCH] lib/xz: remove dead IA-64 (Itanium) support code

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Message-ID: <20251013183800.7af293f5.lasse.collin@tukaani.org>
Date: Mon, 13 Oct 2025 18:38:00 +0300
From: Lasse Collin <lasse.collin@...aani.org>
To: Ankan Biswas <spyjetfayed@...il.com>
Cc: skhan@...uxfoundation.org, khalid@...nel.org,
 david.hunter.linux@...il.com, linux-kernel@...r.kernel.org,
 linux-kernel-mentees@...ts.linux.dev, Phillip Lougher
 <phillip@...ashfs.org.uk>
Subject: Re: [PATCH] lib/xz: remove dead IA-64 (Itanium) support code

On 2025-10-13 Ankan Biswas wrote:
> Support for the IA-64 (Itanium) architecture was removed in
> commit cf8e8658100d ("arch: Remove Itanium (IA-64) architecture").
> 
> This patch drops the IA-64 specific decompression code from
> lib/xz, which was conditionally compiled with the now-obsolete
> CONFIG_XZ_DEC_IA64 option.

The commit cf8e8658100d ("arch: Remove Itanium (IA-64) architecture")
unconditionally disabled the IA-64 filter, which effectively dropped
support for mounting Squashfs file systems that use XZ with the IA-64
filter. I wasn't Cc'ed when it was committed because I wasn't in
MAINTAINERS back then. If I had been, I might have commented that the
commits [1] and [2] and the discussion [3] showed that keeping filters
available for non-native archs can be desirable. But now that time has
passed and no one has complained about the lack of IA-64 filter, it
seems fine to remove it completely from Linux.

I won't remove the IA-64 filter from the upstream version of
xz_dec_bcj.c, so this change will make those files diverge a little
more. That's unfortunate, but they already differ by a tiny amount
anyway.

xz_private.h line 106 checks if XZ_DEC_IA64 is defined. That line
should be removed too. With that change:

    Acked-by: Lasse Collin <lasse.collin@...aani.org>

[1] 5dc49c75a26b ("decompressors: make the default XZ_DEC_* config
    match the selected architecture")
[2] bf4d064d89ae ("lib/xz: enable all filters by default in Kconfig")
[3] https://lore.kernel.org/lkml/20140228230017.GE14970@merlin.infradead.org/T/

-- 
Lasse Collin