linux-kernel - Re: [PATCH v2] /proc/sysrq-trigger: accept multiple keys at once

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Message-ID: <c1100a92-90de-4029-bb9c-8f4b6ee2c552@kernel.org>
Date:   Tue, 14 Nov 2023 10:44:16 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Tomas Mudrunka <tomas.mudrunka@...il.com>,
        gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        corbet@....net, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2] /proc/sysrq-trigger: accept multiple keys at once

On 14. 11. 23, 10:35, Tomas Mudrunka wrote:
> Just for convenience.
> This way we can do:
> `echo _reisub > /proc/sysrq-trigger`
> Instead of:
> `for i in r e i s u b; do echo "$i" > /proc/sysrq-trigger; done;`
> 
> This can be very useful when trying to execute sysrq combo remotely
> or from userspace. When sending keys in multiple separate writes,
> userspace can be killed before whole combo is completed.
> Therefore putting all keys in single write is more robust approach.
> 
> Signed-off-by: Tomas Mudrunka <tomas.mudrunka@...il.com>
> ---
>   Documentation/admin-guide/sysrq.rst |  4 ++++
>   drivers/tty/sysrq.c                 | 17 ++++++++++++++---
>   2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
> index 51906e473..9d46a33e5 100644
> --- a/Documentation/admin-guide/sysrq.rst
> +++ b/Documentation/admin-guide/sysrq.rst
> @@ -79,6 +79,10 @@ On all
>   
>   		echo t > /proc/sysrq-trigger
>   
> +	Alternatively write key combo prepended by underscore. e.g.::
> +
> +		echo _reisub > /proc/sysrq-trigger
> +
>   The :kbd:`<command key>` is case sensitive.
>   
>   What are the 'command' keys?
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 6b4a28bcf..3455e6dd3 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -1150,16 +1150,27 @@ EXPORT_SYMBOL(unregister_sysrq_key);
>   #ifdef CONFIG_PROC_FS
>   /*
>    * writing 'C' to /proc/sysrq-trigger is like sysrq-C
> + * If first character in write is underscore, all characters are interpreted.
>    */
>   static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
>   				   size_t count, loff_t *ppos)
>   {
> -	if (count) {
> +	char bulk = false;

bool

> +	size_t i;
> +
> +	for (i = 0; i < count; i++) {
>   		char c;
>   
> -		if (get_user(c, buf))
> +		if (get_user(c, buf+i))

spaces around +

>   			return -EFAULT;
> -		__handle_sysrq(c, false);
> +
> +		if (c == '_')
> +			bulk = true;
> +		else
> +			__handle_sysrq(c, false);
> +
> +		if (!bulk)
> +			break;
>   	}
>   
>   	return count;

-- 
js
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