linux-kernel - Re: [PATCH 1/2] devres: provide devm_kstrdup

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Message-Id: <20180827103353.GB13848@rapoport-lnx>
Date:   Mon, 27 Aug 2018 13:33:53 +0300
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arend van Spriel <aspriel@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Robin Murphy <robin.murphy@....com>,
        Joe Perches <joe@...ches.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>, Roman Gushchin <guro@...com>,
        Huang Ying <ying.huang@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

On Mon, Aug 27, 2018 at 10:21:00AM +0200, Bartosz Golaszewski wrote:
> Provide a resource managed version of kstrdup_const(). This variant
> internally calls devm_kstrdup() on pointers that are outside of
> .rodata section. Also provide a corresponding version of devm_kfree().
> 
> Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
> ---
>  include/linux/device.h |  2 ++
>  mm/util.c              | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 8f882549edee..f8f5982d26b2 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -693,7 +693,9 @@ static inline void *devm_kcalloc(struct device *dev,
>  	return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
>  }
>  extern void devm_kfree(struct device *dev, void *p);
> +extern void devm_kfree_const(struct device *dev, void *p);
>  extern char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
> +extern char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp);
>  extern void *devm_kmemdup(struct device *dev, const void *src, size_t len,
>  			  gfp_t gfp);
> 
> diff --git a/mm/util.c b/mm/util.c
> index d2890a407332..6d1f41b5775e 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -39,6 +39,20 @@ void kfree_const(const void *x)
>  }
>  EXPORT_SYMBOL(kfree_const);
> 
> +/**
> + * devm_kfree_const - Resource managed conditional kfree
> + * @dev: device this memory belongs to
> + * @p: memory to free
> + *
> + * Function calls devm_kfree only if @p is not in .rodata section.
> + */
> +void devm_kfree_const(struct device *dev, void *p)
> +{
> +	if (!is_kernel_rodata((unsigned long)p))
> +		devm_kfree(dev, p);
> +}
> +EXPORT_SYMBOL(devm_kfree_const);
> +
>  /**
>   * kstrdup - allocate space for and copy an existing string
>   * @s: the string to duplicate
> @@ -78,6 +92,27 @@ const char *kstrdup_const(const char *s, gfp_t gfp)
>  }
>  EXPORT_SYMBOL(kstrdup_const);
> 
> +/**
> + * devm_kstrdup_const - resource managed conditional string duplication
> + * @dev: device for which to duplicate the string
> + * @s: the string to duplicate
> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> + *
> + * Function returns source string if it is in .rodata section otherwise it
> + * fallbacks to devm_kstrdup.

Please make it proper "Returns:" description and move to the end of the
comment. See Documentation/doc-guide/kernel-doc.rst.

> + * Strings allocated by devm_kstrdup_const will be automatically freed when
> + * the associated device is detached.
> + */
> +char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
> +{
> +	if (is_kernel_rodata((unsigned long)s))
> +		return s;
> +
> +	return devm_kstrdup(dev, s, gfp);
> +}
> +EXPORT_SYMBOL(devm_kstrdup_const);
> +

The devm_ variants seem to belong to drivers/base/devres.c rather than
mm/util.c

>  /**
>   * kstrndup - allocate space for and copy an existing string
>   * @s: the string to duplicate
> -- 
> 2.18.0
> 

-- 
Sincerely yours,
Mike.