linux-kernel - Re: [PATCH 1/6] tty: implement write

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Date:   Thu, 21 Jan 2021 10:42:04 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-serial@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oliver Giles <ohw.giles@...il.com>,
        Robert Karszniewicz <r.karszniewicz@...tec.de>
Subject: Re: [PATCH 1/6] tty: implement write_iter

On Thu, Jan 21, 2021 at 9:57 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> Incremental patches please as these are already in my public branches
> and I would have to revert them and add new ones but that's messy, so
> fixes on top is fine.

Ok. And since I think you put that first tty_write conversion patch in
a different branch from the tty_read one, I did the fixup patches for
the two as separate patches, even though they really just do the exact
same thing.

So here's three patches: the two fixups for the hung_up_tty case, and
the EOVERFLOW error case that Jiri also noted. I've also updated the
'tty-splice' branch if you prefer them that way.

And I *should* say that I still haven't tested _any_ of the HDLC
changes. I have no idea how to do that, and if somebody can point to a
test-case (or better yet, actually has a real life situation where
they use it and can test this all) it would be great.

Jiri, any other issues, or any comment of yours I missed? I didn't do
the min() thing, I find the explicit conditional more legible myself,
but won't complain if somebody else then disagrees and wants to clean
it up.

(On the matter of cleanups: when reading through the ICANON handling
in canon_copy_from_read_buf(), that code is really completely
incomprehensible. I know how it works, and why it does it, but I had
to remind myself, because the code just looks crazy and does things
like "*nr+1" to walk _past_ the point we actually copy etc. I was very
tempted to rewrite that entirely, but wanting to keep my changes
minimal and targeted made me not do so).

                Linus

View attachment "0001-tty-fix-up-hung_up_tty_write-conversion.patch" of type "text/x-patch" (1940 bytes)

View attachment "0002-tty-fix-up-hung_up_tty_read-conversion.patch" of type "text/x-patch" (1908 bytes)

View attachment "0003-tty-fix-up-iterate_tty_read-EOVERFLOW-handling.patch" of type "text/x-patch" (2129 bytes)