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Date:   Thu, 4 May 2023 17:58:10 +0900
From:   Greg KH <gregkh@linuxfoundation.org>
To:     "Peng Fan (OSS)" <peng.fan@oss.nxp.com>
Cc:     robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org,
        rafael@kernel.org, andriy.shevchenko@linux.intel.com,
        hdegoede@redhat.com, jgg@ziepe.ca, saravanak@google.com,
        keescook@chromium.org, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, abel.vesa@linaro.org,
        Peng Fan <peng.fan@nxp.com>
Subject: Re: [PATCH] devres: provide API devm_kstrndup
Message-ID: <2023050413-margin-devotedly-468d@gregkh>
References: <20230504075754.372780-1-peng.fan@oss.nxp.com>
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On Thu, May 04, 2023 at 03:57:54PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@nxp.com>
> 
> This patch introduces devm_kstrndup API so that the
> device's driver can allocate memory and copy string.
> 
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
>  drivers/base/devres.c  | 28 ++++++++++++++++++++++++++++
>  include/linux/device.h |  1 +
>  2 files changed, 29 insertions(+)

We can not add apis with no users, please submit this at the same time a
driver needs it.

And what driver would need to copy a string?


> 
> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
> index 5c998cfac335..87e2965e5bab 100644
> --- a/drivers/base/devres.c
> +++ b/drivers/base/devres.c
> @@ -963,6 +963,34 @@ char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp)
>  }
>  EXPORT_SYMBOL_GPL(devm_kstrdup);
>  
> +/**
> + * devm_kstrndup - Allocate resource managed space and
> + *                copy an existing string into that.
> + * @dev: Device to allocate memory for
> + * @s: the string to duplicate
> + * @max: max length to duplicate
> + * @gfp: the GFP mask used in the devm_kmalloc() call when allocating memory
> + * RETURNS:
> + * Pointer to allocated string on success, NULL on failure.
> + */
> +char *devm_kstrndup(struct device *dev, const char *s, size_t max, gfp_t gfp)
> +{
> +	size_t len;
> +	char *buf;
> +
> +	if (!s)
> +		return NULL;
> +
> +	len = strnlen(s, max);
> +	buf = devm_kmalloc(dev, len + 1, gfp);
> +	if (buf) {
> +		memcpy(buf, s, len);
> +		buf[len] = '\0';

Why not use kstrndup() instead of copying the same logic here?

thanks,

greg k-h