diff mbox series

[18/19] linux/include: add non-atomic version of xchg

Message ID 20221222114635.1251934-19-andrzej.hajda@intel.com
State New
Headers
Series Introduce __xchg, non-atomic xchg |

Commit Message

Andrzej Hajda Dec. 22, 2022, 11:46 a.m. UTC 
  The pattern of setting variable with new value and returning old
one is very common in kernel. Usually atomicity of the operation
is not required, so xchg seems to be suboptimal and confusing in
such cases.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
 include/linux/non-atomic/xchg.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 include/linux/non-atomic/xchg.h

Comments

Andy Shevchenko Dec. 22, 2022, 12:47 p.m. UTC | #1 
On Thu, Dec 22, 2022 at 12:46:34PM +0100, Andrzej Hajda wrote:
> The pattern of setting variable with new value and returning old
> one is very common in kernel. Usually atomicity of the operation
> is not required, so xchg seems to be suboptimal and confusing in
> such cases.

FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
> ---
>  include/linux/non-atomic/xchg.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>  create mode 100644 include/linux/non-atomic/xchg.h
> 
> diff --git a/include/linux/non-atomic/xchg.h b/include/linux/non-atomic/xchg.h
> new file mode 100644
> index 00000000000000..f7fa5dd746f37d
> --- /dev/null
> +++ b/include/linux/non-atomic/xchg.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_NON_ATOMIC_XCHG_H
> +#define _LINUX_NON_ATOMIC_XCHG_H
> +
> +/**
> + * __xchg - set variable pointed by @ptr to @val, return old value
> + * @ptr: pointer to affected variable
> + * @val: value to be written
> + *
> + * This is non-atomic variant of xchg.
> + */
> +#define __xchg(ptr, val) ({		\
> +	__auto_type __ptr = ptr;	\
> +	__auto_type __t = *__ptr;	\
> +	*__ptr = (val);			\
> +	__t;				\
> +})
> +
> +#endif
> -- 
> 2.34.1
>
diff mbox series

Patch

diff --git a/include/linux/non-atomic/xchg.h b/include/linux/non-atomic/xchg.h
new file mode 100644
index 00000000000000..f7fa5dd746f37d
--- /dev/null
+++ b/include/linux/non-atomic/xchg.h
@@ -0,0 +1,19 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_NON_ATOMIC_XCHG_H
+#define _LINUX_NON_ATOMIC_XCHG_H
+
+/**
+ * __xchg - set variable pointed by @ptr to @val, return old value
+ * @ptr: pointer to affected variable
+ * @val: value to be written
+ *
+ * This is non-atomic variant of xchg.
+ */
+#define __xchg(ptr, val) ({		\
+	__auto_type __ptr = ptr;	\
+	__auto_type __t = *__ptr;	\
+	*__ptr = (val);			\
+	__t;				\
+})
+
+#endif