Messages in this thread Patch in this message | | | Date | Sun, 26 Feb 2023 23:00:56 +0530 | From | Deepak R Varma <> | Subject | [PATCH v3 2/3] perf/x86/intel/pt: Use sysfs_emit() in show() callback function |
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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@mailo.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@infradead.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
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