[PATCH] cleancache: constify cleancache_ops structure

[PATCH] cleancache: constify cleancache_ops structure

[Julia Lawall]

The cleancache_ops structure is never modified, so declare it as const.

This also removes the __read_mostly declaration on the cleancache_ops
variable declaration, since it seems redundant with const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>

---

Not sure that the __read_mostly change is correct.  Does it apply to the
variable, or to what the variable points to?

 drivers/xen/tmem.c         |    2 +-
 include/linux/cleancache.h |    2 +-
 mm/cleancache.c            |    4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
index bda5ec0b4..cb3e142 100644
--- a/include/linux/cleancache.h
+++ b/include/linux/cleancache.h
@@ -37,7 +37,7 @@ struct cleancache_ops {
 	void (*invalidate_fs)(int);
 };
 
-extern int cleancache_register_ops(struct cleancache_ops *ops);
+extern int cleancache_register_ops(const struct cleancache_ops *ops);
 extern void __cleancache_init_fs(struct super_block *);
 extern void __cleancache_init_shared_fs(struct super_block *);
 extern int  __cleancache_get_page(struct page *);
diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index 945fc43..4ac2ca8 100644
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -242,7 +242,7 @@ static int tmem_cleancache_init_shared_fs(char *uuid, size_t pagesize)
 	return xen_tmem_new_pool(shared_uuid, TMEM_POOL_SHARED, pagesize);
 }
 
-static struct cleancache_ops tmem_cleancache_ops = {
+static const struct cleancache_ops tmem_cleancache_ops = {
 	.put_page = tmem_cleancache_put_page,
 	.get_page = tmem_cleancache_get_page,
 	.invalidate_page = tmem_cleancache_flush_page,
diff --git a/mm/cleancache.c b/mm/cleancache.c
index 8fc5081..c6356d6 100644
--- a/mm/cleancache.c
+++ b/mm/cleancache.c
@@ -22,7 +22,7 @@
  * cleancache_ops is set by cleancache_register_ops to contain the pointers
  * to the cleancache "backend" implementation functions.
  */
-static struct cleancache_ops *cleancache_ops __read_mostly;
+static const struct cleancache_ops *cleancache_ops;
 
 /*
  * Counters available via /sys/kernel/debug/cleancache (if debugfs is
@@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
 /*
  * Register operations for cleancache. Returns 0 on success.
  */
-int cleancache_register_ops(struct cleancache_ops *ops)
+int cleancache_register_ops(const struct cleancache_ops *ops)
 {
 	if (cmpxchg(&cleancache_ops, NULL, ops))
 		return -EBUSY;

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Re: [PATCH] cleancache: constify cleancache_ops structure

[Konrad Rzeszutek Wilk]

On Wed, Dec 23, 2015 at 10:06:24PM +0100, Julia Lawall wrote:
> The cleancache_ops structure is never modified, so declare it as const.
> 
> This also removes the __read_mostly declaration on the cleancache_ops
> variable declaration, since it seems redundant with const.
> 
> Done with the help of Coccinelle.
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> 
> ---
> 
> Not sure that the __read_mostly change is correct.  Does it apply to the
> variable, or to what the variable points to?

It should just put the structure in the right section (.rodata).

Thanks for the patch!
> 
>  drivers/xen/tmem.c         |    2 +-
>  include/linux/cleancache.h |    2 +-
>  mm/cleancache.c            |    4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
> index bda5ec0b4..cb3e142 100644
> --- a/include/linux/cleancache.h
> +++ b/include/linux/cleancache.h
> @@ -37,7 +37,7 @@ struct cleancache_ops {
>  	void (*invalidate_fs)(int);
>  };
>  
> -extern int cleancache_register_ops(struct cleancache_ops *ops);
> +extern int cleancache_register_ops(const struct cleancache_ops *ops);
>  extern void __cleancache_init_fs(struct super_block *);
>  extern void __cleancache_init_shared_fs(struct super_block *);
>  extern int  __cleancache_get_page(struct page *);
> diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
> index 945fc43..4ac2ca8 100644
> --- a/drivers/xen/tmem.c
> +++ b/drivers/xen/tmem.c
> @@ -242,7 +242,7 @@ static int tmem_cleancache_init_shared_fs(char *uuid, size_t pagesize)
>  	return xen_tmem_new_pool(shared_uuid, TMEM_POOL_SHARED, pagesize);
>  }
>  
> -static struct cleancache_ops tmem_cleancache_ops = {
> +static const struct cleancache_ops tmem_cleancache_ops = {
>  	.put_page = tmem_cleancache_put_page,
>  	.get_page = tmem_cleancache_get_page,
>  	.invalidate_page = tmem_cleancache_flush_page,
> diff --git a/mm/cleancache.c b/mm/cleancache.c
> index 8fc5081..c6356d6 100644
> --- a/mm/cleancache.c
> +++ b/mm/cleancache.c
> @@ -22,7 +22,7 @@
>   * cleancache_ops is set by cleancache_register_ops to contain the pointers
>   * to the cleancache "backend" implementation functions.
>   */
> -static struct cleancache_ops *cleancache_ops __read_mostly;
> +static const struct cleancache_ops *cleancache_ops;
>  
>  /*
>   * Counters available via /sys/kernel/debug/cleancache (if debugfs is
> @@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
>  /*
>   * Register operations for cleancache. Returns 0 on success.
>   */
> -int cleancache_register_ops(struct cleancache_ops *ops)
> +int cleancache_register_ops(const struct cleancache_ops *ops)
>  {
>  	if (cmpxchg(&cleancache_ops, NULL, ops))
>  		return -EBUSY;
> 

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Re: [PATCH] cleancache: constify cleancache_ops structure

[Rasmus Villemoes]

On Wed, Jan 20 2016, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:

> On Wed, Dec 23, 2015 at 10:06:24PM +0100, Julia Lawall wrote:
>> The cleancache_ops structure is never modified, so declare it as const.
>> 
>> This also removes the __read_mostly declaration on the cleancache_ops
>> variable declaration, since it seems redundant with const.
>> 
>> Done with the help of Coccinelle.
>> 
>> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
>> 
>> ---
>> 
>> Not sure that the __read_mostly change is correct.  Does it apply to the
>> variable, or to what the variable points to?
>
> It should just put the structure in the right section (.rodata).
>
> Thanks for the patch!

The __read_mostly marker should probably be left there...

>>   */
>> -static struct cleancache_ops *cleancache_ops __read_mostly;
>> +static const struct cleancache_ops *cleancache_ops;
>>  
>>  /*
>>   * Counters available via /sys/kernel/debug/cleancache (if debugfs is
>> @@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
>>  /*
>>   * Register operations for cleancache. Returns 0 on success.
>>   */
>> -int cleancache_register_ops(struct cleancache_ops *ops)
>> +int cleancache_register_ops(const struct cleancache_ops *ops)
>>  {
>>  	if (cmpxchg(&cleancache_ops, NULL, ops))
>>  		return -EBUSY;
>>

I don't know this code, but I assume that this is mostly a one-time
thing, so once cleancache_ops gets its value assigned, it doesn't
change, and that's what the __read_mostly is about (it applies to the
object declared, not whatever it happens to point to).

(Also, the commit message is slightly inaccurate: it is
tmem_cleancache_ops which is never changed and hence declared const;
changing the various pointers to it to const is just a necessary followup).

Rasmus

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Re: [PATCH] cleancache: constify cleancache_ops structure

[Julia Lawall]

On Thu, 21 Jan 2016, Rasmus Villemoes wrote:

> On Wed, Jan 20 2016, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> 
> > On Wed, Dec 23, 2015 at 10:06:24PM +0100, Julia Lawall wrote:
> >> The cleancache_ops structure is never modified, so declare it as const.
> >> 
> >> This also removes the __read_mostly declaration on the cleancache_ops
> >> variable declaration, since it seems redundant with const.
> >> 
> >> Done with the help of Coccinelle.
> >> 
> >> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> >> 
> >> ---
> >> 
> >> Not sure that the __read_mostly change is correct.  Does it apply to the
> >> variable, or to what the variable points to?
> >
> > It should just put the structure in the right section (.rodata).
> >
> > Thanks for the patch!
> 
> The __read_mostly marker should probably be left there...

I sent a corrected version this afternoon.

> 
> >>   */
> >> -static struct cleancache_ops *cleancache_ops __read_mostly;
> >> +static const struct cleancache_ops *cleancache_ops;
> >>  
> >>  /*
> >>   * Counters available via /sys/kernel/debug/cleancache (if debugfs is
> >> @@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
> >>  /*
> >>   * Register operations for cleancache. Returns 0 on success.
> >>   */
> >> -int cleancache_register_ops(struct cleancache_ops *ops)
> >> +int cleancache_register_ops(const struct cleancache_ops *ops)
> >>  {
> >>  	if (cmpxchg(&cleancache_ops, NULL, ops))
> >>  		return -EBUSY;
> >>
> 
> I don't know this code, but I assume that this is mostly a one-time
> thing, so once cleancache_ops gets its value assigned, it doesn't
> change, and that's what the __read_mostly is about (it applies to the
> object declared, not whatever it happens to point to).
> 
> (Also, the commit message is slightly inaccurate: it is
> tmem_cleancache_ops which is never changed and hence declared const;
> changing the various pointers to it to const is just a necessary followup).

OK, in general, I have referred to the type rather than the structure name 
in these patches, since there can be more than one structure.

julia

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Re: [Xen-devel] [PATCH] cleancache: constify cleancache_ops structure

[David Vrabel]

On 23/12/15 21:06, Julia Lawall wrote:
> The cleancache_ops structure is never modified, so declare it as const.
> 
> This also removes the __read_mostly declaration on the cleancache_ops
> variable declaration, since it seems redundant with const.
> 
> Done with the help of Coccinelle.
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> 
> ---
> 
> Not sure that the __read_mostly change is correct.  Does it apply to the
> variable, or to what the variable points to?

The variable, so...

> --- a/mm/cleancache.c
> +++ b/mm/cleancache.c
> @@ -22,7 +22,7 @@
>   * cleancache_ops is set by cleancache_register_ops to contain the pointers
>   * to the cleancache "backend" implementation functions.
>   */
> -static struct cleancache_ops *cleancache_ops __read_mostly;
> +static const struct cleancache_ops *cleancache_ops;

...you want to retain the __read_mostly here.

David

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Re: [Xen-devel] [PATCH] cleancache: constify cleancache_ops structure

[Julia Lawall]

On Thu, 21 Jan 2016, David Vrabel wrote:

> On 23/12/15 21:06, Julia Lawall wrote:
> > The cleancache_ops structure is never modified, so declare it as const.
> >
> > This also removes the __read_mostly declaration on the cleancache_ops
> > variable declaration, since it seems redundant with const.
> >
> > Done with the help of Coccinelle.
> >
> > Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> >
> > ---
> >
> > Not sure that the __read_mostly change is correct.  Does it apply to the
> > variable, or to what the variable points to?
>
> The variable, so...

Thanks.  I'll update the patch, unless you have already fixed it.

julia

> > --- a/mm/cleancache.c
> > +++ b/mm/cleancache.c
> > @@ -22,7 +22,7 @@
> >   * cleancache_ops is set by cleancache_register_ops to contain the pointers
> >   * to the cleancache "backend" implementation functions.
> >   */
> > -static struct cleancache_ops *cleancache_ops __read_mostly;
> > +static const struct cleancache_ops *cleancache_ops;
>
> ...you want to retain the __read_mostly here.
>
> David
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[Xen-devel] [PATCH v2] cleancache: constify cleancache_ops structure

[Julia Lawall]

The cleancache_ops structure is never modified, so declare it as const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>

---

v2: put back the read mostly

 drivers/xen/tmem.c         |    2 +-
 include/linux/cleancache.h |    2 +-
 mm/cleancache.c            |    4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
index bda5ec0b4..cb3e142 100644
--- a/include/linux/cleancache.h
+++ b/include/linux/cleancache.h
@@ -37,7 +37,7 @@ struct cleancache_ops {
 	void (*invalidate_fs)(int);
 };

-extern int cleancache_register_ops(struct cleancache_ops *ops);
+extern int cleancache_register_ops(const struct cleancache_ops *ops);
 extern void __cleancache_init_fs(struct super_block *);
 extern void __cleancache_init_shared_fs(struct super_block *);
 extern int  __cleancache_get_page(struct page *);
diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index 945fc43..4ac2ca8 100644
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -242,7 +242,7 @@ static int tmem_cleancache_init_shared_fs(char *uuid, size_t pagesize)
 	return xen_tmem_new_pool(shared_uuid, TMEM_POOL_SHARED, pagesize);
 }

-static struct cleancache_ops tmem_cleancache_ops = {
+static const struct cleancache_ops tmem_cleancache_ops = {
 	.put_page = tmem_cleancache_put_page,
 	.get_page = tmem_cleancache_get_page,
 	.invalidate_page = tmem_cleancache_flush_page,
diff --git a/mm/cleancache.c b/mm/cleancache.c
index 8fc5081..c6356d6 100644
--- a/mm/cleancache.c
+++ b/mm/cleancache.c
@@ -22,7 +22,7 @@
  * cleancache_ops is set by cleancache_register_ops to contain the pointers
  * to the cleancache "backend" implementation functions.
  */
-static struct cleancache_ops *cleancache_ops __read_mostly;
+static const struct cleancache_ops *cleancache_ops __read_mostly;

 /*
  * Counters available via /sys/kernel/debug/cleancache (if debugfs is
@@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
 /*
  * Register operations for cleancache. Returns 0 on success.
  */
-int cleancache_register_ops(struct cleancache_ops *ops)
+int cleancache_register_ops(const struct cleancache_ops *ops)
 {
 	if (cmpxchg(&cleancache_ops, NULL, ops))
 		return -EBUSY;

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Re: [Xen-devel] [PATCH v2] cleancache: constify cleancache_ops structure

[Konrad Rzeszutek Wilk]

On Thu, Jan 21, 2016 at 04:47:29PM +0100, Julia Lawall wrote:
> The cleancache_ops structure is never modified, so declare it as const.
> 
> Done with the help of Coccinelle.

I will pull it in my tree and sent it to Linus.

Thanks!
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> 
> ---
> 
> v2: put back the read mostly
> 
>  drivers/xen/tmem.c         |    2 +-
>  include/linux/cleancache.h |    2 +-
>  mm/cleancache.c            |    4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
> index bda5ec0b4..cb3e142 100644
> --- a/include/linux/cleancache.h
> +++ b/include/linux/cleancache.h
> @@ -37,7 +37,7 @@ struct cleancache_ops {
>  	void (*invalidate_fs)(int);
>  };
> 
> -extern int cleancache_register_ops(struct cleancache_ops *ops);
> +extern int cleancache_register_ops(const struct cleancache_ops *ops);
>  extern void __cleancache_init_fs(struct super_block *);
>  extern void __cleancache_init_shared_fs(struct super_block *);
>  extern int  __cleancache_get_page(struct page *);
> diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
> index 945fc43..4ac2ca8 100644
> --- a/drivers/xen/tmem.c
> +++ b/drivers/xen/tmem.c
> @@ -242,7 +242,7 @@ static int tmem_cleancache_init_shared_fs(char *uuid, size_t pagesize)
>  	return xen_tmem_new_pool(shared_uuid, TMEM_POOL_SHARED, pagesize);
>  }
> 
> -static struct cleancache_ops tmem_cleancache_ops = {
> +static const struct cleancache_ops tmem_cleancache_ops = {
>  	.put_page = tmem_cleancache_put_page,
>  	.get_page = tmem_cleancache_get_page,
>  	.invalidate_page = tmem_cleancache_flush_page,
> diff --git a/mm/cleancache.c b/mm/cleancache.c
> index 8fc5081..c6356d6 100644
> --- a/mm/cleancache.c
> +++ b/mm/cleancache.c
> @@ -22,7 +22,7 @@
>   * cleancache_ops is set by cleancache_register_ops to contain the pointers
>   * to the cleancache "backend" implementation functions.
>   */
> -static struct cleancache_ops *cleancache_ops __read_mostly;
> +static const struct cleancache_ops *cleancache_ops __read_mostly;
> 
>  /*
>   * Counters available via /sys/kernel/debug/cleancache (if debugfs is
> @@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
>  /*
>   * Register operations for cleancache. Returns 0 on success.
>   */
> -int cleancache_register_ops(struct cleancache_ops *ops)
> +int cleancache_register_ops(const struct cleancache_ops *ops)
>  {
>  	if (cmpxchg(&cleancache_ops, NULL, ops))
>  		return -EBUSY;
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

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