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Date:   Tue, 30 May 2023 11:45:00 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Loic Poulain <loic.poulain@linaro.org>
Cc:     corbet@lwn.net, viro@zeniv.linux.org.uk,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] init: Add support for rootwait timeout parameter
Message-ID: <20230530-polytechnisch-besten-258f74577eff@brauner>
References: <20230526130716.2932507-1-loic.poulain@linaro.org>
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In-Reply-To: <20230526130716.2932507-1-loic.poulain@linaro.org>
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On Fri, May 26, 2023 at 03:07:16PM +0200, Loic Poulain wrote:
> Add an optional timeout arg to 'rootwait' as the maximum time in
> seconds to wait for the root device to show up before attempting
> forced mount of the root filesystem.
> 
> This can be helpful to force boot failure and restart in case the
> root device does not show up in time, allowing the bootloader to
> take any appropriate measures (e.g. recovery, A/B switch, retry...).
> 
> In success case, mounting happens as soon as the root device is ready,
> contrary to the existing 'rootdelay' parameter (unconditional delay).
> 
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
> ---

Not terribly opposed and not terribly convinced yet.
So, we have rootdelay= with a timeout parameter that allows to specify a
delay before attempting to mount the root device. And we have rootwait
currently as an indefinite wait. Adding a timeout for rootwait doesn't
seem crazy and is backwards compatible. But there's no mention of any
concrete users or use-case for this which is usually preferable. If this
is just "could be useful for someone eventually" it's way less desirable
to merge this than when it's "here's a/multiple user/users"... So I
would love to see a use-case described here.

And this is only useful if there isn't an early userspace init that
parses and manages root=. So we need to hit prepare_namespaces() as a
rootwait timeout isn't meaningful if this is done by and early init in
the initramfs for example.