On 09.12.2022 18:16, Arnd Bergmann wrote:
On Fri, Dec 9, 2022, at 16:48, 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. Since name xchg is already in use and __xchg is used
in architecture code, proposition is to name the macro exchange.
Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
While I generally don't like type invariant calling conventions
of xchg() and cmpxchg(), having a new function that has a similar
name without being able to tell which one is which from the
name seems more confusing.
Since __xchg() is only used on 11 architectures as an internal
Quite big number for 'only' :)
name for the backing of arch_xchg() or arch_xchg_relaxed(),
maybe we can instead rename those to __arch_xchg() and use the
__xchg() name for the new non-atomic version?
I will try, but even compile test will be some challenge, need to find
cross-compilers for these archs.
Btw exchange is not totally new name, for example C++ uses it [1].
[1]: https://en.cppreference.com/w/cpp/utility/exchange
Regards
Andrzej
+/**
+ * exchange - 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 exchange(ptr, val) ({ \
+ typeof(ptr) __ptr = ptr; \
+ typeof(*__ptr) __t = *__ptr; \
I think you can better express this using __auto_type than typeof(),
it is now provided by all supported compilers now.
Arnd
