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Date:   Sat, 14 Nov 2020 01:17:54 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>,
        Greg KH <gregkh@linuxfoundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
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        kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org, linux-hyperv@vger.kernel.org
Subject: Re: [PATCH 1/6] seq_file: add seq_read_iter
Message-ID: <20201114011754.GL3576660@ZenIV.linux.org.uk>
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On Fri, Nov 13, 2020 at 04:54:53PM -0700, Nathan Chancellor wrote:

> This patch in -next (6a9f696d1627bacc91d1cebcfb177f474484e8ba) breaks
> WSL2's interoperability feature, where Windows paths automatically get
> added to PATH on start up so that Windows binaries can be accessed from
> within Linux (such as clip.exe to pipe output to the clipboard). Before,
> I would see a bunch of Linux + Windows folders in $PATH but after, I
> only see the Linux folders (I can give you the actual PATH value if you
> care but it is really long).
> 
> I am not at all familiar with the semantics of this patch or how
> Microsoft would be using it to inject folders into PATH (they have some
> documentation on it here:
> https://docs.microsoft.com/en-us/windows/wsl/interop) and I am not sure
> how to go about figuring that out to see why this patch breaks something
> (unless you have an idea). I have added the Hyper-V maintainers and list
> to CC in case they know someone who could help.

Out of curiosity: could you slap WARN_ON(!iov_iter_count(iter)); right in
the beginning of seq_read_iter() and see if that triggers?