linux-kernel - Re: [PATCH] Revert "linux/types.h: remove unnecessary __bitwise_

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Date:   Wed, 25 May 2022 09:02:19 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Michael S . Tsirkin" <mst@...hat.com>, llvm@...ts.linux.dev,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] Revert "linux/types.h: remove unnecessary __bitwise__"

On Wed, May 25, 2022 at 7:46 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> This reverts commit c724c866bb70cb8c607081a26823a1f0ebde4387.
>
> Jiri Slaby reported that c724c866bb70 ("linux/types.h: remove unnecessary
> __bitwise__") broke userspace, including open-iscsi, because it uses
> __bitwise__.
>
> Restore the __bitwise__ definition.

Hmm.

Presumably it's only the uapi case that actually wants to re-instate it.

And I'd rather make that "__bitwise__" case explicitly special, with a
comment about why it exists when the kernel itself doesn't use it.

IOW, rather than the revert, maybe something like the below
(whitespace-damaged) instead?

Jiri, does something like this work for you?

                 Linus

---
 include/uapi/linux/types.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/uapi/linux/types.h b/include/uapi/linux/types.h
index c4dc597f3dcf..308433be33c2 100644
--- a/include/uapi/linux/types.h
+++ b/include/uapi/linux/types.h
@@ -26,6 +26,9 @@
 #define __bitwise
 #endif

+/* The kernel doesn't use this legacy form, but user space does */
+#define __bitwise__ __bitwise
+
 typedef __u16 __bitwise __le16;
 typedef __u16 __bitwise __be16;
 typedef __u32 __bitwise __le32;