linux-kernel - [PATCH v3 2/3] perf/x86/intel/pt: Use sysfs

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Message-ID: <75e2b1f55156d8341e722eb923c9304a13def2b2.1677431992.git.drv@mailo.com>
Date:   Sun, 26 Feb 2023 23:00:56 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>,
        Deepak R Varma <drv@...lo.com>
Subject: [PATCH v3 2/3] perf/x86/intel/pt: Use sysfs_emit() in show()
 callback function

As per C99 standard, snprintf() returns the number of bytes that would
be encoded in the destination buffer when it is sufficiently large. This
return value may be different from what the caller is expecting and hence
may lead to potential errors in the program.
Kernel release 2.6.2 introduced scnprintf() & vscnprintf() which precisely
return the actual bytes encoded into the destination buffer.

For the sysfs attribute show() callback functions, which returns the number
of bytes to the user space, a more recent recommendation is to use
sysfs_emit() or sysfs_emit_at() instead of sprintf() family of functions.
This is recorded in the Documentation/filesystems/sysfs.rst Kernel
documentation file.

Issue identified using the coccinelle device_attr_show.cocci script.

Signed-off-by: Deepak R Varma <drv@...lo.com>
---
Changes in v3:
   - None.

Changes in v2:
   - Revise patch log message to include details on the potential issues with
     current implementation and how the proposal is a better solution.
     Feedback provided by Peter Zijlstra <peterz@...radead.org>

 arch/x86/events/intel/pt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 42a55794004a..d9e6d771b458 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -96,7 +96,7 @@ static ssize_t pt_cap_show(struct device *cdev,
 		container_of(attr, struct dev_ext_attribute, attr);
 	enum pt_capabilities cap = (long)ea->var;
 
-	return snprintf(buf, PAGE_SIZE, "%x\n", intel_pt_validate_hw_cap(cap));
+	return sysfs_emit(buf, "%x\n", intel_pt_validate_hw_cap(cap));
 }
 
 static struct attribute_group pt_cap_group __ro_after_init = {
-- 
2.34.1