linux-kernel - Re: [GIT PULL] 9p update for 5.7

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Message-ID: <20200407021626.cd3wwbg7ayiwt4ry@l29ah-x201.l29ah-x201>
Date:   Tue, 7 Apr 2020 05:16:26 +0300
From:   L29Ah <l29ah@...k.li>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        v9fs-developer@...ts.sourceforge.net
Subject: Re: [GIT PULL] 9p update for 5.7

On Mon, Apr 06, 2020 at 06:40:57PM +0200, Dominique Martinet wrote:
> The use-case here is stuff like reading from synthetic files (think fake
> pipes) where data comes in like a pipe and one would want read to return
> as soon as data is available.
> Just thinking out loud it might be possible to make pipes go through the
> server and somewhat work, but this might bring its own share of other
> problems and existing programs would need to be changed (e.g. wmii's
> synthetic filesystem exposes this kind of files as well as regular
> files, which works fine for their userspace client (wmiir) but can't
> really be used with a linux client)

> Anyway, I agree looking at O_NONBLOCK for that isn't obvious.
> I agree with the usecase here and posix allows short reads regardless of
> the flag so the behaviour is legal either way ; the filesystem is
> allowed to return whenever it wants on a whim - let's just add some docs
> as you suggest unless Sergey has something to add.

In fact i would prefer disabling the full reads unconditionally, but AFAIR some userspace programs might interpret a short read as EOF (and also would need to check the logic that motivated the kernel-side looping).

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