[PATCH] perf/x86/amd/core: Use sysfs_emit() in show() callback function

[PATCH] perf/x86/amd/core: Use sysfs_emit() in show() callback function

[Deepak R Varma]

Using sprintf/snprintf functions are error prone and suggested to be
replaced by scnprintf/vscnrptintf as outlined in this [1] LWN article.

A more recent recommendation is to use sysfs_emit() or sysfs_emit_at()
as per Documentation/filesystems/sysfs.rst in show() callback function
when formatting values to be returned to user-space. These helper
functions are PAGE_SIZE aware and wrap a safer call to vscnprintf().

[1] https://lwn.net/Articles/69419/

Issue identified using the coccinelle device_attr_show.cocci script.

Signed-off-by: Deepak R Varma <drv@mailo.com>
---
 arch/x86/events/amd/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 4386b10682ce..47a3a841332a 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -1272,7 +1272,7 @@ static ssize_t branches_show(struct device *cdev,
 			      struct device_attribute *attr,
 			      char *buf)
 {
-	return snprintf(buf, PAGE_SIZE, "%d\n", x86_pmu.lbr_nr);
+	return sysfs_emit(buf, "%d\n", x86_pmu.lbr_nr);
 }
 
 static DEVICE_ATTR_RO(branches);
-- 
2.34.1

Re: [PATCH] perf/x86/amd/core: Use sysfs_emit() in show() callback function

[Peter Zijlstra]

On Fri, Feb 17, 2023 at 10:12:57PM +0530, Deepak R Varma wrote:
> Using sprintf/snprintf functions are error prone and suggested to be
> replaced by scnprintf/vscnrptintf as outlined in this [1] LWN article.
> 
> A more recent recommendation is to use sysfs_emit() or sysfs_emit_at()
> as per Documentation/filesystems/sysfs.rst in show() callback function
> when formatting values to be returned to user-space. These helper
> functions are PAGE_SIZE aware and wrap a safer call to vscnprintf().
> 
> [1] https://lwn.net/Articles/69419/
> 
> Issue identified using the coccinelle device_attr_show.cocci script.

This Changelog fails to inform me of what the actual problem is and why
the proposed solution is better.

As such I cannot form an opinion on the patch and must decline.

(Also, I'm not going to chase down random links on the interweb,
Changelogs should be self contained)