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Date:   Fri, 20 May 2022 03:31:40 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] random: convert to using fops->write_iter()
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On Thu, May 19, 2022 at 09:25:30PM -0600, Jens Axboe wrote:

> > Feed it a buffer with only 1 byte mapped, watch it'll pass to mix_pool_bytes().
> > And see how much of 'block' has been used uninitialized...
> 
> I don't follow? Buffer with 1 byte, iter setup with 1 byte. We copy 1 byte,
> and we pass 1 byte to mix_pool_bytes(). What am I missing?

"only 1 byte mapped" != "len is 1"...  Anonymous mmap() of 2*PAGE_SIZE, munmap()
the second half, ask that sucker to write PAGE_SIZE from buffer + PAGE_SIZE - 1...