[PATCH v1] platform/x86: wmi: Replace kmalloc + sprintf() with kasprintf()

[PATCH v1] platform/x86: wmi: Replace kmalloc + sprintf() with kasprintf()

[Andy Shevchenko]

kasprintf() does the job of two: kmalloc() and sprintf().
Replace two calls with one.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/platform/x86/wmi.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index c0c8945603cb..4e76ffcb5394 100644
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -933,12 +933,11 @@ static int wmi_dev_probe(struct device *dev)
 			goto probe_failure;
 		}
 
-		buf = kmalloc(strlen(wdriver->driver.name) + 5, GFP_KERNEL);
+		buf = kasprintf(GFP_KERNEL, "wmi/%s", wdriver->driver.name);
 		if (!buf) {
 			ret = -ENOMEM;
 			goto probe_string_failure;
 		}
-		sprintf(buf, "wmi/%s", wdriver->driver.name);
 		wblock->char_dev.minor = MISC_DYNAMIC_MINOR;
 		wblock->char_dev.name = buf;
 		wblock->char_dev.fops = &wmi_fops;
-- 
2.16.1

RE: [PATCH v1] platform/x86: wmi: Replace kmalloc + sprintf() with kasprintf()

[David Laight]

From: Andy Shevchenko
> Sent: 16 February 2018 15:40
>
> kasprintf() does the job of two: kmalloc() and sprintf().
> Replace two calls with one.
...
> -		buf = kmalloc(strlen(wdriver->driver.name) + 5, GFP_KERNEL);
> +		buf = kasprintf(GFP_KERNEL, "wmi/%s", wdriver->driver.name);
...

Except that kasprintf() has no idea how long a buffer is needed.
It might even do the printf twice just to get the length.

	David

Re: [PATCH v1] platform/x86: wmi: Replace kmalloc + sprintf() with kasprintf()

[Andy Shevchenko]

On Fri, Feb 16, 2018 at 5:55 PM, David Laight <David.Laight@aculab.com> wrote:

>> kasprintf() does the job of two: kmalloc() and sprintf().
>> Replace two calls with one.
> ...
>> -             buf = kmalloc(strlen(wdriver->driver.name) + 5, GFP_KERNEL);
>> +             buf = kasprintf(GFP_KERNEL, "wmi/%s", wdriver->driver.name);
> ...
>
> Except that kasprintf() has no idea how long a buffer is needed.

Hmm...

> It might even do the printf twice just to get the length.

It does exactly that. So what?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v1] platform/x86: wmi: Replace kmalloc + sprintf() with kasprintf()

[Darren Hart]

On Fri, Feb 16, 2018 at 03:55:24PM +0000, David Laight wrote:
> From: Andy Shevchenko
> > Sent: 16 February 2018 15:40
> >
> > kasprintf() does the job of two: kmalloc() and sprintf().
> > Replace two calls with one.
> ...
> > -		buf = kmalloc(strlen(wdriver->driver.name) + 5, GFP_KERNEL);
> > +		buf = kasprintf(GFP_KERNEL, "wmi/%s", wdriver->driver.name);
> ...
> 
> Except that kasprintf() has no idea how long a buffer is needed.
> It might even do the printf twice just to get the length.

Sure, but this is one-time and non-critical path. Unfortunately there
isn't any guidance in Documentation here. Of the 520 or so instances of
kasprintf usages in the kernel, device name or similar is a very common
pattern. Eliminating manual counting of characters for buffer allocation
seems like a good plan to me.

So unless we want to argue that all those use cases are wrong, this
would appear to be at least common practice, if not best practice for
this particular pattern.

Reviewed-by: Darren Hart (VMware) <dvhart@infradead.org>

-- 
Darren Hart
VMware Open Source Technology Center