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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sun, 20 Sep 2020 18:00:03 +0200
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Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
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On Sun, Sep 20, 2020 at 5:15 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Fri, Sep 18, 2020 at 02:45:25PM +0200, Christoph Hellwig wrote:
> > Add a flag to force processing a syscall as a compat syscall.  This is
> > required so that in_compat_syscall() works for I/O submitted by io_uring
> > helper threads on behalf of compat syscalls.
>
> Al doesn't like this much, but my suggestion is to introduce two new
> opcodes -- IORING_OP_READV32 and IORING_OP_WRITEV32.  The compat code
> can translate IORING_OP_READV to IORING_OP_READV32 and then the core
> code can know what that user pointer is pointing to.

How is that different from the current approach of storing the ABI as
a flag in ctx->compat?

     Arnd