[PATCH] Input: atkbd - simplify atkbd_show_force_release()

[PATCH] Input: atkbd - simplify atkbd_show_force_release()

[Rasmus Villemoes]

We can just include the newline in the format string, and scnprintf()
guarantees nul-termination. These days, sysfs_emit() is
preferred in sysfs ->show methods, so switch to that.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 drivers/input/keyboard/atkbd.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/input/keyboard/atkbd.c b/drivers/input/keyboard/atkbd.c
index edc613efc158..b146a3ec631a 100644
--- a/drivers/input/keyboard/atkbd.c
+++ b/drivers/input/keyboard/atkbd.c
@@ -1492,13 +1492,8 @@ static ssize_t atkbd_set_extra(struct atkbd *atkbd, const char *buf, size_t coun
 
 static ssize_t atkbd_show_force_release(struct atkbd *atkbd, char *buf)
 {
-	size_t len = scnprintf(buf, PAGE_SIZE - 1, "%*pbl",
-			       ATKBD_KEYMAP_SIZE, atkbd->force_release_mask);
-
-	buf[len++] = '\n';
-	buf[len] = '\0';
-
-	return len;
+	return sysfs_emit(buf, "%*pbl\n",
+			  ATKBD_KEYMAP_SIZE, atkbd->force_release_mask);
 }
 
 static ssize_t atkbd_set_force_release(struct atkbd *atkbd,
-- 
2.29.2

Re: [PATCH] Input: atkbd - simplify atkbd_show_force_release()

[Dmitry Torokhov]

Hi Rasmus,

On Wed, Apr 21, 2021 at 10:16:39PM +0200, Rasmus Villemoes wrote:
> We can just include the newline in the format string, and scnprintf()
> guarantees nul-termination. These days, sysfs_emit() is
> preferred in sysfs ->show methods, so switch to that.

Technically speaking the conversion is not 100% equivalent - original
code ensured that there is always a newline in the output. I kind of
like this, so maybe we need sysfs_emit_nl() or similar?

> 
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
>  drivers/input/keyboard/atkbd.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/input/keyboard/atkbd.c b/drivers/input/keyboard/atkbd.c
> index edc613efc158..b146a3ec631a 100644
> --- a/drivers/input/keyboard/atkbd.c
> +++ b/drivers/input/keyboard/atkbd.c
> @@ -1492,13 +1492,8 @@ static ssize_t atkbd_set_extra(struct atkbd *atkbd, const char *buf, size_t coun
>  
>  static ssize_t atkbd_show_force_release(struct atkbd *atkbd, char *buf)
>  {
> -	size_t len = scnprintf(buf, PAGE_SIZE - 1, "%*pbl",
> -			       ATKBD_KEYMAP_SIZE, atkbd->force_release_mask);
> -
> -	buf[len++] = '\n';
> -	buf[len] = '\0';
> -
> -	return len;
> +	return sysfs_emit(buf, "%*pbl\n",
> +			  ATKBD_KEYMAP_SIZE, atkbd->force_release_mask);
>  }
>  
>  static ssize_t atkbd_set_force_release(struct atkbd *atkbd,
> -- 
> 2.29.2
> 

Thanks.

-- 
Dmitry

Re: [PATCH] Input: atkbd - simplify atkbd_show_force_release()

[Rasmus Villemoes]

On 25/04/2021 04.27, Dmitry Torokhov wrote:
> Hi Rasmus,
> 
> On Wed, Apr 21, 2021 at 10:16:39PM +0200, Rasmus Villemoes wrote:
>> We can just include the newline in the format string, and scnprintf()
>> guarantees nul-termination. These days, sysfs_emit() is
>> preferred in sysfs ->show methods, so switch to that.
> 
> Technically speaking the conversion is not 100% equivalent - original
> code ensured that there is always a newline in the output. I kind of
> like this, so maybe we need sysfs_emit_nl() or similar?

(1) From a UX perspective, it actually seems better to have lack of
trailing newline as a (though subtle) indicator that the output was
truncated

(2) Given that ATKBD_KEYMAP_SIZE is 512, I don't see how that could
actually ever happen. AFAICT, the worst case %pbl representation is when
the bitmap consists of a series two set bits and one unset bit, yielding
a pattern of "xxx-yyy," (with yyy=xxx+1) for 8 characters per 3 bits, or
about 1365 characters (slight overestimate because of one- and two-digit
numbers).