2022-09-26 19:16:32

by Jules Irenge

Subject: [PATCH 5/7] kernel/cpu: Convert snprintf() to scnprintf()

Coccinnelle reports a warning
Warning: Use scnprintf or sprintf
Adding to that, there has been a slow migration from snprintf to scnprintf.
This LWN article explains the rationale for this change
https: //lwn.net/Articles/69419/
Ie. snprintf() returns what *would* be the resulting length,
while scnprintf() returns the actual length.

Signed-off-by: Jules Irenge <[email protected]>
---
kernel/cpu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index bbad5e375d3b..f358d89c9580 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2512,7 +2512,7 @@ static ssize_t control_show(struct device *dev,
{
const char *state = smt_states[cpu_smt_control];

- return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
+ return scnprintf(buf, PAGE_SIZE - 2, "%s\n", state);
}

static ssize_t control_store(struct device *dev, struct device_attribute *attr,
@@ -2525,7 +2525,7 @@ static DEVICE_ATTR_RW(control);
static ssize_t active_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
- return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
+ return scnprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
}
static DEVICE_ATTR_RO(active);

--
2.37.3

2022-09-28 09:50:26

by Steven Price

Subject: Re: [PATCH 5/7] kernel/cpu: Convert snprintf() to scnprintf()

On 26/09/2022 19:52, Jules Irenge wrote:
> Coccinnelle reports a warning
> Warning: Use scnprintf or sprintf
> Adding to that, there has been a slow migration from snprintf to scnprintf.
> This LWN article explains the rationale for this change
> https: //lwn.net/Articles/69419/
> Ie. snprintf() returns what *would* be the resulting length,
> while scnprintf() returns the actual length.
>
> Signed-off-by: Jules Irenge <[email protected]>

Using sysfs_emit() would be even better in this case, although it's
slightly different because it outputs a maximum of PAGE_SIZE rather than
PAGE_SIZE - 2 bytes. But I can't see any reason for that "- 2" - it
appears to have been added when the sysfs entry was added by Thomas
Gleixner in commit 05736e4ac13c ("cpu/hotplug: Provide knobs to control
SMT") but I don't see any justification for it.

Steve

> ---
> kernel/cpu.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index bbad5e375d3b..f358d89c9580 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -2512,7 +2512,7 @@ static ssize_t control_show(struct device *dev,
> {
> const char *state = smt_states[cpu_smt_control];
>
> - return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
> + return scnprintf(buf, PAGE_SIZE - 2, "%s\n", state);
> }
>
> static ssize_t control_store(struct device *dev, struct device_attribute *attr,
> @@ -2525,7 +2525,7 @@ static DEVICE_ATTR_RW(control);
> static ssize_t active_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> - return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
> + return scnprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
> }
> static DEVICE_ATTR_RO(active);
>