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Date:   Mon, 16 Nov 2020 03:29:42 +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>,
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        wei.liu@kernel.org, linux-hyperv@vger.kernel.org
Subject: Re: [PATCH 1/6] seq_file: add seq_read_iter
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On Sun, Nov 15, 2020 at 05:34:16PM -0700, Nathan Chancellor wrote:
 
> Still good.
> 
> Tested-by: Nathan Chancellor <natechancellor@gmail.com>

Pushed into #fixes

> > 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.

Oh, well...  Anyway, as a regression test it's interesting:

#include <sys/uio.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
main()
{
	static char s[1024];
	static struct iovec v[2] = {{NULL, 0}, {s, 1024}};

	for(;;) {
		ssize_t n = readv(0, v, 2), m, w;

		if (n < 0) {
			perror("readv");
			return -1;
		}
		if (!n)
			return 0;
		for (m = 0; m < n; m += w) {
			w = write(1, s + m, n - m);
			if (w < 0)
				perror("write");
		}
	}
}

which ought to copy stdin to stdout; with this bug it would (on sufficiently
large seq_file-based files) fail with "readv: Bad address" (-EFAULT, that is).