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Message-ID: <CABPSWR5cG=xTA72BHayYQTb=24VS3N+=dbsiMcU+gyqTKvNXAQ@mail.gmail.com>
Date: Fri, 5 Sep 2025 22:57:31 +0530
From: vivek yadav <vivekyadav1207731111@...il.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: daniel.lezcano@...aro.org, linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org, joe@...ches.com
Subject: Re: [PATCH] cpuidle: sysfs: Use sysfs_emit/sysfs_emit_at instead of sprintf/scnprintf
On Mon, Aug 25, 2025 at 8:58 PM <vivekyadav1207731111@...il.com> wrote:
>>
>> From: Vivek Yadav <vivekyadav1207731111@...il.com>
>>
>> The ->show() callbacks in sysfs should use sysfs_emit() or
>> sysfs_emit_at() when formatting values for user space. These helpers
>> are the recommended way to ensure correct buffer handling and
>> consistency across the kernel.
>>
>> See Documentation/filesystems/sysfs.rst for details.
>>
>> No functional change intended.
>>
>> Suggested-by: Joe Perches <joe@...ches.com>
>> Signed-off-by: Vivek Yadav <vivekyadav1207731111@...il.com>
>> ---
>> drivers/cpuidle/sysfs.c | 38 +++++++++++++++++++-------------------
>> 1 file changed, 19 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
>> index d6f5da61cb7d..c7af09460b74 100644
>> --- a/drivers/cpuidle/sysfs.c
>> +++ b/drivers/cpuidle/sysfs.c
>> @@ -22,21 +22,21 @@ static ssize_t show_available_governors(struct device *dev,
>> struct device_attribute *attr,
>> char *buf)
>> {
>> - ssize_t i = 0;
>> + ssize_t len = 0;
>
>The variable rename is not necessary or even useful AFAICS ->
There is no harm if we leave the variable name as 'i' but it would be better
if we give it a suitable name like 'offset'. It will definitely improve
readability.
>
>> struct cpuidle_governor *tmp;
>>
>> mutex_lock(&cpuidle_lock);
>> list_for_each_entry(tmp, &cpuidle_governors, governor_list) {
>> - if (i >= (ssize_t) (PAGE_SIZE - (CPUIDLE_NAME_LEN + 2)))
>> + if (len >= (ssize_t)(PAGE_SIZE - (CPUIDLE_NAME_LEN + 2)))
>> goto out;
>>
>> - i += scnprintf(&buf[i], CPUIDLE_NAME_LEN + 1, "%s ", tmp->name);
>> + len += sysfs_emit_at(buf, len, "%.*s ", CPUIDLE_NAME_LEN, tmp->name);
>
>-> because the second argument here is still an offset relative to
>buf, isn't it?
I think 'len' is also not a good name. Now I have two options.
Either I can remove this part from the patch or I can make new patch
where I can change the variable name 'i' into a more meaningful name
like 'offset'.
Let me know in which direction I should move.
~Vivek
On Fri, Sep 5, 2025 at 1:05 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Mon, Aug 25, 2025 at 8:58 PM <vivekyadav1207731111@...il.com> wrote:
> >
> > From: Vivek Yadav <vivekyadav1207731111@...il.com>
> >
> > The ->show() callbacks in sysfs should use sysfs_emit() or
> > sysfs_emit_at() when formatting values for user space. These helpers
> > are the recommended way to ensure correct buffer handling and
> > consistency across the kernel.
> >
> > See Documentation/filesystems/sysfs.rst for details.
> >
> > No functional change intended.
> >
> > Suggested-by: Joe Perches <joe@...ches.com>
> > Signed-off-by: Vivek Yadav <vivekyadav1207731111@...il.com>
> > ---
> > drivers/cpuidle/sysfs.c | 38 +++++++++++++++++++-------------------
> > 1 file changed, 19 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
> > index d6f5da61cb7d..c7af09460b74 100644
> > --- a/drivers/cpuidle/sysfs.c
> > +++ b/drivers/cpuidle/sysfs.c
> > @@ -22,21 +22,21 @@ static ssize_t show_available_governors(struct device *dev,
> > struct device_attribute *attr,
> > char *buf)
> > {
> > - ssize_t i = 0;
> > + ssize_t len = 0;
>
> The variable rename is not necessary or even useful AFAICS ->
>
> > struct cpuidle_governor *tmp;
> >
> > mutex_lock(&cpuidle_lock);
> > list_for_each_entry(tmp, &cpuidle_governors, governor_list) {
> > - if (i >= (ssize_t) (PAGE_SIZE - (CPUIDLE_NAME_LEN + 2)))
> > + if (len >= (ssize_t)(PAGE_SIZE - (CPUIDLE_NAME_LEN + 2)))
> > goto out;
> >
> > - i += scnprintf(&buf[i], CPUIDLE_NAME_LEN + 1, "%s ", tmp->name);
> > + len += sysfs_emit_at(buf, len, "%.*s ", CPUIDLE_NAME_LEN, tmp->name);
>
> -> because the second argument here is still an offset relative to
> buf, isn't it?
>
> > }
> >
> > out:
> > - i+= sprintf(&buf[i], "\n");
> > + len += sysfs_emit_at(buf, len, "\n");
> > mutex_unlock(&cpuidle_lock);
> > - return i;
> > + return len;
> > }
> >
> > static ssize_t show_current_driver(struct device *dev,
> > @@ -49,9 +49,9 @@ static ssize_t show_current_driver(struct device *dev,
> > spin_lock(&cpuidle_driver_lock);
> > drv = cpuidle_get_driver();
> > if (drv)
> > - ret = sprintf(buf, "%s\n", drv->name);
> > + ret = sysfs_emit(buf, "%s\n", drv->name);
> > else
> > - ret = sprintf(buf, "none\n");
> > + ret = sysfs_emit(buf, "none\n");
> > spin_unlock(&cpuidle_driver_lock);
> >
> > return ret;
> > @@ -65,9 +65,9 @@ static ssize_t show_current_governor(struct device *dev,
> >
> > mutex_lock(&cpuidle_lock);
> > if (cpuidle_curr_governor)
> > - ret = sprintf(buf, "%s\n", cpuidle_curr_governor->name);
> > + ret = sysfs_emit(buf, "%s\n", cpuidle_curr_governor->name);
> > else
> > - ret = sprintf(buf, "none\n");
> > + ret = sysfs_emit(buf, "none\n");
> > mutex_unlock(&cpuidle_lock);
> >
> > return ret;
> > @@ -230,7 +230,7 @@ static struct cpuidle_state_attr attr_##_name = __ATTR(_name, 0644, show, store)
> > static ssize_t show_state_##_name(struct cpuidle_state *state, \
> > struct cpuidle_state_usage *state_usage, char *buf) \
> > { \
> > - return sprintf(buf, "%u\n", state->_name);\
> > + return sysfs_emit(buf, "%u\n", state->_name);\
> > }
> >
> > #define define_show_state_ull_function(_name) \
> > @@ -238,7 +238,7 @@ static ssize_t show_state_##_name(struct cpuidle_state *state, \
> > struct cpuidle_state_usage *state_usage, \
> > char *buf) \
> > { \
> > - return sprintf(buf, "%llu\n", state_usage->_name);\
> > + return sysfs_emit(buf, "%llu\n", state_usage->_name);\
> > }
> >
> > #define define_show_state_str_function(_name) \
> > @@ -247,8 +247,8 @@ static ssize_t show_state_##_name(struct cpuidle_state *state, \
> > char *buf) \
> > { \
> > if (state->_name[0] == '\0')\
> > - return sprintf(buf, "<null>\n");\
> > - return sprintf(buf, "%s\n", state->_name);\
> > + return sysfs_emit(buf, "<null>\n");\
> > + return sysfs_emit(buf, "%s\n", state->_name);\
> > }
> >
> > #define define_show_state_time_function(_name) \
> > @@ -256,7 +256,7 @@ static ssize_t show_state_##_name(struct cpuidle_state *state, \
> > struct cpuidle_state_usage *state_usage, \
> > char *buf) \
> > { \
> > - return sprintf(buf, "%llu\n", ktime_to_us(state->_name##_ns)); \
> > + return sysfs_emit(buf, "%llu\n", ktime_to_us(state->_name##_ns)); \
> > }
> >
> > define_show_state_time_function(exit_latency)
> > @@ -273,14 +273,14 @@ static ssize_t show_state_time(struct cpuidle_state *state,
> > struct cpuidle_state_usage *state_usage,
> > char *buf)
> > {
> > - return sprintf(buf, "%llu\n", ktime_to_us(state_usage->time_ns));
> > + return sysfs_emit(buf, "%llu\n", ktime_to_us(state_usage->time_ns));
> > }
> >
> > static ssize_t show_state_disable(struct cpuidle_state *state,
> > struct cpuidle_state_usage *state_usage,
> > char *buf)
> > {
> > - return sprintf(buf, "%llu\n",
> > + return sysfs_emit(buf, "%llu\n",
> > state_usage->disable & CPUIDLE_STATE_DISABLED_BY_USER);
> > }
> >
> > @@ -310,7 +310,7 @@ static ssize_t show_state_default_status(struct cpuidle_state *state,
> > struct cpuidle_state_usage *state_usage,
> > char *buf)
> > {
> > - return sprintf(buf, "%s\n",
> > + return sysfs_emit(buf, "%s\n",
> > state->flags & CPUIDLE_FLAG_OFF ? "disabled" : "enabled");
> > }
> >
> > @@ -358,7 +358,7 @@ static ssize_t show_state_s2idle_##_name(struct cpuidle_state *state, \
> > struct cpuidle_state_usage *state_usage, \
> > char *buf) \
> > { \
> > - return sprintf(buf, "%llu\n", state_usage->s2idle_##_name);\
> > + return sysfs_emit(buf, "%llu\n", state_usage->s2idle_##_name);\
> > }
> >
> > define_show_state_s2idle_ull_function(usage);
> > @@ -550,7 +550,7 @@ static ssize_t show_driver_name(struct cpuidle_driver *drv, char *buf)
> > ssize_t ret;
> >
> > spin_lock(&cpuidle_driver_lock);
> > - ret = sprintf(buf, "%s\n", drv ? drv->name : "none");
> > + ret = sysfs_emit(buf, "%s\n", drv ? drv->name : "none");
> > spin_unlock(&cpuidle_driver_lock);
> >
> > return ret;
> > --
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