On 22.12.2022 15:12, Geert Uytterhoeven wrote:
Hi Andrzej, Thanks for your series! On Thu, Dec 22, 2022 at 12:49 PM Andrzej Hajda <andrzej.hajda@xxxxxxxxx> wrote:I hope there will be place for such tiny helper in kernel. Quick cocci analyze shows there is probably few thousands places where it could be useful. I am not sure who is good person to review/ack such patches, so I've used my intuition to construct to/cc lists, sorry for mistakes. This is the 2nd approach of the same idea, with comments addressed[0]. The helper is tiny and there are advices we can leave without it, so I want to present few arguments why it would be good to have it: 1. Code readability/simplification/number of lines: Real example from drivers/net/ethernet/mellanox/mlx5/core/esw/qos.c: - previous_min_rate = evport->qos.min_rate; - evport->qos.min_rate = min_rate; + previous_min_rate = __xchg(evport->qos.min_rate, min_rate);Upon closer look, shouldn't that be previous_min_rate = __xchg(&evport->qos.min_rate, min_rate); ?
Yes, you are right, the first argument is a pointer. Regards Andrzej
For sure the code is more compact, and IMHO more readable. 2. Presence of similar helpers in other somehow related languages/libs: a) Rust[1]: 'replace' from std::mem module, there is also 'take' helper (__xchg(&x, 0)), which is the same as private helper in i915 - fetch_and_zero, see latest patch. b) C++ [2]: 'exchange' from utility header. If the idea is OK there are still 2 qestions to answer: 1. Name of the helper, __xchg follows kernel conventions, but for me Rust names are also OK.Before I realized the missing "&", I wondered how this is different from swap(), so naming is important. https://elixir.bootlin.com/linux/latest/source/include/linux/minmax.h#L139 Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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