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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 11 Apr 2022 20:49:13 -1000
Message-ID: <CAHk-=wjfLQdsjMBRQm=UB+RB08Cs6G41+kk2ybe7JHuu4ydhRQ@mail.gmail.com>
Subject: Re: [PATCH] stat: don't fail if the major number is >= 256
To:     Mikulas Patocka <mpatocka@redhat.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Matthew Wilcox <willy@infradead.org>
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On Mon, Apr 11, 2022 at 7:37 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Correct. It's literally the compat structure that has no basis in reality.
>
> Or it might be some truly ancient thing, but I really don't think so.

I was intrigued, so I went back and checked.

        unsigned short st_dev;
        unsigned short __pad1;

is in fact historical. But it was changed to

        unsigned long  st_dev;

(for i386, so this is a 32-bit 'unsigned long') on April 2, 2003.

From the BK tree conversion:

    https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=e95b2065677fe32512a597a79db94b77b90c968d

so I think we should just make sure that the 64-bit compat system call
is compatible with that 2003+ state, not with some truly ancient
state.

                      Linus