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    Subject[PATCH v3] cpumask: add cpumask_var_t documentation
    Date
    > On Thu, Apr 28, 2011 at 12:27 PM, KOSAKI Motohiro
    > <kosaki.motohiro@jp.fujitsu.com> wrote:
    > > cpumask_var_t has one nortable difference against cpumask_t.
    > > This patch adds the explanation.
    > >
    > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > > ---
    > >  include/linux/cpumask.h |   14 ++++++++++++++
    > >  1 files changed, 14 insertions(+), 0 deletions(-)
    > >
    > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
    > > index 1e40dd0..471c98a 100644
    > > --- a/include/linux/cpumask.h
    > > +++ b/include/linux/cpumask.h
    > > @@ -617,6 +617,20 @@ static inline size_t cpumask_size(void)
    > >  *       ... use 'tmpmask' like a normal struct cpumask * ...
    > >  *
    > >  *     free_cpumask_var(tmpmask);
    > > + *
    > > + *
    > > + * However, one notable exception is there. cpumask_var_t is allocated
    > > + * only nr_cpu_ids bits
    >
    > Maybe, instead of "is allocated only", "allocates only" ?

    Instead, "alloc_cpumask_var() allocates only nr_cpu_ids bits" is more clear? :)


    > > (in the other hand, real cpumask_t always has
    > > + * NR_CPUS bits). therefore You don't have to dereference cpumask_var_t.
    >
    > s/therefore You/Therefore you/ ?
    >

    Thx.


    > > + *
    > > + *     cpumask_var_t tmpmask;
    > > + *     if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
    > > + *             return -ENOMEM;
    > > + *
    > > + *     var = *tmpmask;
    > > + *
    > > + * This code makes NR_CPUS length memcopy and bring memroy corruption.
    >
    > /s/memroy/memory
    >
    > You are saying that I should not use this code? I'm confused, could
    > you explain a little bit?

    Yes. you aren't confused.


    > > + * You have to use cpumask_copy() instead.
    > >  */
    >
    > I don't get this. :(

    "cpumask_copy() privide safe copy functionality." is clear?


    From d2ea9d4846e46bcc8a82b9a641ede3a10aca346c Mon Sep 17 00:00:00 2001
    From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Date: Tue, 26 Apr 2011 19:58:39 +0900
    Subject: [PATCH v3] cpumask: add cpumask_var_t documentation

    cpumask_var_t has one nortable difference against cpumask_t.
    This patch adds the explanation.

    Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    ---
    include/linux/cpumask.h | 14 ++++++++++++++
    1 files changed, 14 insertions(+), 0 deletions(-)

    diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
    index 1e40dd0..e2b9032 100644
    --- a/include/linux/cpumask.h
    +++ b/include/linux/cpumask.h
    @@ -617,6 +617,20 @@ static inline size_t cpumask_size(void)
    * ... use 'tmpmask' like a normal struct cpumask * ...
    *
    * free_cpumask_var(tmpmask);
    + *
    + *
    + * However, one notable exception is there. alloc_cpumask_var() allocates
    + * only nr_cpumask_bits bits (in the other hand, real cpumask_t always has
    + * NR_CPUS bits). Therefore you don't have to dereference cpumask_var_t.
    + *
    + * cpumask_var_t tmpmask;
    + * if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
    + * return -ENOMEM;
    + *
    + * var = *tmpmask;
    + *
    + * This code makes NR_CPUS length memcopy and bring memory corruption.
    + * cpumask_copy() privide safe copy functionality.
    */
    #ifdef CONFIG_CPUMASK_OFFSTACK
    typedef struct cpumask *cpumask_var_t;
    --
    1.7.3.1


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