linux-kernel - Re: [PATCH RFC 2/2] sysfs: add helper macro for showing simple integer values

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Date:   Sun, 30 Aug 2020 11:13:53 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Alex Dewar <alex.dewar90@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        "David S. Miller" <davem@...emloft.net>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 2/2] sysfs: add helper macro for showing simple
 integer values

On Sun, Aug 30, 2020 at 12:37:17AM +0100, Alex Dewar wrote:
> sysfs attributes are supposed to be only single values, which are
> printed into a buffer of PAGE_SIZE. Accordingly, for many simple
> attributes, sprintf() can be used like so:
> 	static ssize_t my_show(..., char *buf)
> 	{
> 		...
> 		return sprintf("%d\n", my_integer);
> 	}
> 
> The problem is that whilst this use of sprintf() is memory safe, other
> cases where e.g. a possibly unterminated string is passed as input, are
> not and so use of sprintf() here might make it more difficult to
> identify these problematic cases.
> 
> Define a macro, sysfs_sprinti(), which outputs the value of a single
> integer to a buffer (with terminating "\n\0") and returns the size written.
> This way, we can convert over the some of the trivially correct users of
> sprintf() and decrease its usage in the kernel source tree.
> 
> Another advantage of this approach is that we can now statically check
> the type of the integer so that e.g. an unsigned long long will be
> formatted as %llu. This will fix cases where the wrong format string has
> been passed to sprintf().
> 
> Signed-off-by: Alex Dewar <alex.dewar90@...il.com>
> ---
>  include/linux/sysfs.h | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)

Did you try this out?  Don't you need to return the number of bytes
written?

I like Joe's patches better, this feels like more work...

thanks,

greg k-h