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

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Message-ID: <CAMRc=McVQ6co1KispVNotLOj4t6Pok0F+j4X9eYnrpDTm-CYaQ@mail.gmail.com>
Date:   Mon, 27 Aug 2018 11:01:57 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Joe Perches <joe@...ches.com>
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>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        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 <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

2018-08-27 10:42 GMT+02:00 Joe Perches <joe@...ches.com>:
> On Mon, 2018-08-27 at 10:21 +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().
> []
>> diff --git a/mm/util.c b/mm/util.c
> []
>>  /**
>>   * 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.
>> + *
>> + * 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);
>
> Doesn't this lose constness and don't you get
> a compiler warning here?
>

Yes it does but for some reason gcc 6.3 didn't complain...

> The kstrdup_const function returns a const char *,
> why shouldn't this?
>

It probably should, I'll fix it for v2.

Bart