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Date: Fri, 3 May 2019 22:53:56 +0000
From: Eric Wong <e@80x24.org>
To: Stephen Demjanenko <sdemjanenko@gmail.com>
Cc: unicorn-public@bogomips.org
Subject: Re: [PATCH] Rescue failed pipe resizes due to permissions
Message-ID: <20190503225356.76cpbof5qvc5djyi@dcvr>
References: <1556922018-24096-1-git-send-email-sdemjanenko@gmail.com>
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sdemjanenko@gmail.com wrote:

Thanks, patch looks good; though I'd like to confirm
some things below for the sake of documentation.

> The `EPERM` error gets raised by the Linux kernel if:
> ```
> (too_many_pipe_buffers_hard(pipe->user) ||
> too_many_pipe_buffers_soft(pipe->user)) &&
> !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)
> ```

Which kernel are you running?
Modern kernels prefix that condition with:

	if (nr_pages > pipe->buffers &&

Scanning kernel changes with `git log -p -L:pipe_set_size:fs/pipe.c',
I see that check was added in b0b91d18e2e97b741b294af9333824ecc3fadfd8
("pipe: fix limit checking in pipe_set_size()")
which was fixed in Linux v4.9+ and v3.16.57+

https://80x24.org/mirrors/linux.git/commit?id=b0b91d18e2e97b741b294af9333824ecc3fadfd8
https://lore.kernel.org/lkml/?q=s%3A%22fix+limit+checking+in+pipe_set_size%22

> Given that the resize is not strictly necessary Unicorn should
> rescue the error and continue booting.

Agreed.  Applied, tested and pushed to master as
commit 5c613c6ea98541df587193e861364c858a8a0abd
Thanks!

Will tag and release v5.5.1 in a day or two.