linux-kernel - Re: [PATCH] proc: Use seq_read

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Message-ID: <20210428061259.GA5084@lst.de>
Date:   Wed, 28 Apr 2021 08:12:59 +0200
From:   Christoph Hellwig <hch@....de>
To:     "Arkadiusz Kozdra (Arusekk)" <arek_koz@...pl>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] proc: Use seq_read_iter where possible

On Tue, Apr 27, 2021 at 08:34:15PM +0200, Arkadiusz Kozdra (Arusekk) wrote:
> Since seq_read_iter looks mature enough to be used for all procfs files,
> re-allow applications to perform zero-copy data forwarding from them.
> According to the sendfile(2) man-page, it is still enough for the file
> being read to support mmap-like operations, and the proc files support
> memory mapping, so returning -EINVAL was an inconsistency.

Linus did object to blindly switching over all instances.

> Some executable-inspecting tools rely on patching entry point
> instructions with minimal machine code that uses sendfile to read
> /proc/self/maps to stdout.  The sendfile call allows them to do it
> faster and without excessive allocations.

Patching what entry point?