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

[Greg Kroah-Hartman]

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@xxxxxxxxx>
> ---
>  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