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Message-ID: <1d363177-2629-1ab3-7a4b-bc67d94bb87a@infradead.org>
Date:   Wed, 26 Jul 2023 23:08:35 -0700
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Subject: Re: [PATCH v2] init: Add support for rootwait timeout parameter
Content-Language: en-US
To:     Loic Poulain <loic.poulain@linaro.org>, brauner@kernel.org,
        viro@zeniv.linux.org.uk, corbet@lwn.net
Cc:     linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, hch@infradead.org
References: <20230726152232.932288-1-loic.poulain@linaro.org>
From:   Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <20230726152232.932288-1-loic.poulain@linaro.org>
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Hi--

On 7/26/23 08:22, 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.
> 
> Use case:
> In case of device mapper usage for the rootfs (e.g. root=/dev/dm-0),
> if the mapper is not able to create the virtual block for any reason
> (wrong arguments, bad dm-verity signature, etc), the `rootwait` param
> causes the kernel to wait forever. It may however be desirable to only
> wait for a given time and then panic (force mount) to cause device reset.
> This gives the bootloader a chance to detect the problem and to take some
> measures, such as marking the booted partition as bad (for A/B case) or
> entering a recovery mode.
> 
> In success case, mounting happens as soon as the root device is ready,
> unlike the existing 'rootdelay' parameter which performs an unconditional
> pause.
> 
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
> ---
>  v2: rebase + reword: add use case example
> 
>  .../admin-guide/kernel-parameters.txt         |  4 ++++
>  init/do_mounts.c                              | 19 +++++++++++++++++--
>  2 files changed, 21 insertions(+), 2 deletions(-)
> 

> diff --git a/init/do_mounts.c b/init/do_mounts.c
> index 1aa015883519..118f2bbe7b38 100644
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -18,6 +18,7 @@
>  #include <linux/slab.h>
>  #include <linux/ramfs.h>
>  #include <linux/shmem_fs.h>
> +#include <linux/ktime.h>
>  
>  #include <linux/nfs_fs.h>
>  #include <linux/nfs_fs_sb.h>
> @@ -71,12 +72,20 @@ static int __init rootwait_setup(char *str)
>  {
>  	if (*str)
>  		return 0;
> -	root_wait = 1;
> +	root_wait = -1;
>  	return 1;
>  }
>  
>  __setup("rootwait", rootwait_setup);
>  
> +static int __init rootwait_timeout_setup(char *str)
> +{
> +	root_wait = simple_strtoul(str, NULL, 0);

Better to use kstrtoul().  simple_strtoul() says:

 * This function has caveats. Please use kstrtoul instead.

and kstrtoul() says:

 * Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
 * Preferred over simple_strtoul(). Return code must be checked.

> +	return 1;
> +}
> +
> +__setup("rootwait=", rootwait_timeout_setup);


-- 
~Randy