linux-kernel - Re: [PATCH] powercap: sscanf return value error handling

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Message-ID: <CAJZ5v0i6EA4QZUOrT28HfhuoYG_BPsC2g6aGTHdMRrzuzcTs6g@mail.gmail.com>
Date: Mon, 15 Dec 2025 12:34:58 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Sumeet Pawnikar <sumeet4linux@...il.com>
Cc: rafael@...nel.org, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powercap: sscanf return value error handling

On Sun, Dec 7, 2025 at 4:16 PM Sumeet Pawnikar <sumeet4linux@...il.com> wrote:
>
> Inconsistent error handling for sscanf() return value check.
> It uses implicit boolean conversion instead of explicit return
> value check. The code checks if (!sscanf(...)) which is incorrect
> because:
>  1. sscanf returns the number of successfully parsed items
>  2. On success, it returns 1 (one item passed)
>  3. On failure, it returns 0 or EOF
>  4. The check 'if (!sscanf(...))' is wrong because it treats
>     success (1) as failure
>
> All occurrences of sscanf() now uses explicit return value check.
> With this behavior it returns '-EINVAL' when parsing fails (returns
> 0 or EOF), and continues when parsing succeeds (returns 1).
>
> Signed-off-by: Sumeet Pawnikar <sumeet4linux@...il.com>
> ---
>  drivers/powercap/powercap_sys.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/powercap/powercap_sys.c b/drivers/powercap/powercap_sys.c
> index bdc65e040d17..e998454e4bf6 100644
> --- a/drivers/powercap/powercap_sys.c
> +++ b/drivers/powercap/powercap_sys.c
> @@ -68,7 +68,7 @@ static ssize_t show_constraint_##_attr(struct device *dev, \
>         int id; \
>         struct powercap_zone_constraint *pconst;\
>         \
> -       if (!sscanf(dev_attr->attr.name, "constraint_%d_", &id)) \
> +       if (sscanf(dev_attr->attr.name, "constraint_%d_", &id) != 1) \
>                 return -EINVAL; \
>         if (id >= power_zone->const_id_cnt)     \
>                 return -EINVAL; \
> @@ -93,7 +93,7 @@ static ssize_t store_constraint_##_attr(struct device *dev,\
>         int id; \
>         struct powercap_zone_constraint *pconst;\
>         \
> -       if (!sscanf(dev_attr->attr.name, "constraint_%d_", &id)) \
> +       if (sscanf(dev_attr->attr.name, "constraint_%d_", &id) != 1) \
>                 return -EINVAL; \
>         if (id >= power_zone->const_id_cnt)     \
>                 return -EINVAL; \
> @@ -162,7 +162,7 @@ static ssize_t show_constraint_name(struct device *dev,
>         ssize_t len = -ENODATA;
>         struct powercap_zone_constraint *pconst;
>
> -       if (!sscanf(dev_attr->attr.name, "constraint_%d_", &id))
> +       if (sscanf(dev_attr->attr.name, "constraint_%d_", &id) != 1)
>                 return -EINVAL;
>         if (id >= power_zone->const_id_cnt)
>                 return -EINVAL;
> --

Applied as 6.19-rc material, thanks!