Re: [PATCH] vfs: uapi: retire octal and hex numbers in favor of (1 << n) for O_ flags

[Geert Uytterhoeven]

	Hi Jori,

> A recent build failure[1] exposed the diffculty of working with the
> current octal and hex definitions of O_ flags when trying to find a gap
> for a new flag. This difficulty is compounded by the fact that O_ flags
> may have architectural specific values.
> 
> Replace the hex/octal #defines, which are hard to parse when looking for
> free bits, with explicit bit shifts like (1 << 11). Also, add comments
> that identify which architectures redefine some of the seemingly free
> ("cursed") bits in uapi/asm-generic/fcntl.h. These should not be used to
> define new O_ flags (for now, at least).
> 
> The translastion was done with Claude Opus 4.8, and verified with a
> (non-AI) gawk script. The accounting of which architectures claim
> which bit-gaps in uapi/asm-generic/fcntl.h is also done by hand.
> 
> [1]: https://lore.kernel.org/all/agruPPybCx8q2XcJ@xxxxxxxxxxxxx/
> 
> Assisted-by: Claude:Opus 4.8
> Signed-off-by: Jori Koolstra <jkoolstra@xxxxxxxxx>

Thanks for your patch, which is now commit 0da79c259ad0554b ("vfs:
uapi: retire octal and hex numbers in favor of (1 << n) for O_
flags").

> --- a/include/uapi/asm-generic/fcntl.h
> +++ b/include/uapi/asm-generic/fcntl.h
> @@ -15,51 +15,55 @@
>   * When introducing new O_* bits, please check its uniqueness in fcntl_init().
>   */
> 
> -#define O_ACCMODE	00000003
> -#define O_RDONLY	00000000
> -#define O_WRONLY	00000001
> -#define O_RDWR		00000002
> +#define O_ACCMODE	3
> +#define O_RDONLY	0
> +#define O_WRONLY	(1 << 0)
> +#define O_RDWR		(1 << 1)

And suddenly all these constants became signed? Can't that cause subtle
issues, especially for uapi headers?

	#define O_ACCMODE	3U
	#define O_RDONLY	0
	#define O_WRONLY	(1U << 0)
	#define O_RDWR		(1U << 1)

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