Re: [PATCH 1/6] seq_file: add seq_read_iter

From: Nathan Chancellor <natechancellor@gmail.com>
To: Al Viro <viro@zeniv.linux.org.uk>
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>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	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
Date: Sun, 15 Nov 2020 17:34:16 -0700	[thread overview]
Message-ID: <20201116003416.GA345@Ryzen-9-3900X.localdomain> (raw)
In-Reply-To: <20201116002513.GU3576660@ZenIV.linux.org.uk>

On Mon, Nov 16, 2020 at 12:25:13AM +0000, Al Viro wrote:
> On Sun, Nov 15, 2020 at 04:51:49PM -0700, Nathan Chancellor wrote:
> > Looks good to me on top of d4d50710a8b46082224376ef119a4dbb75b25c56,
> > thanks for quickly looking into this!
> > 
> > Tested-by: Nathan Chancellor <natechancellor@gmail.com>
> 
> OK... a variant with (hopefully) better comments and cleaned up
> logics in the second loop (
>                 if (seq_has_overflowed(m) || err) {
>                         m->count = offs;
>                         if (likely(err <= 0))
>                                 break;
>                 }
> replaced with
>                 if (err > 0) {          // ->show() says "skip it"
>                         m->count = offs;
>                 } else if (err || seq_has_overflowed(m)) {
>                         m->count = offs;
>                         break;
>                 }
> ) follows.  I'm quite certain that it is an equivalent transformation
> (seq_has_overflowed() has no side effects) and IMO it's slightly
> more readable that way.  Survives local beating; could you check if
> it's still OK with your testcase?  Equivalent transformation or not,
> I'd rather not slap anyone's Tested-by: on a modified variant of
> patch...

Still good.

Tested-by: Nathan Chancellor <natechancellor@gmail.com>

> BTW, is that call of readv() really coming from init?  And if it
> is, what version of init are you using?

I believe that it is but since this is WSL2, I believe that /init is a
proprietary Microsoft implementation, rather than systemd or another
init system:

https://wiki.ubuntu.com/WSL#Keeping_Ubuntu_Updated_in_WSL

So I am not sure how possible it is to see exactly what is going on or
getting it improved.

Cheers,
Nathan