Re: [musl] Re: [PATCH resent] uapi libc compat: allow non-glibc to opt out of uapi definitions

On 03/08/2017 05:39 PM, Carlos O'Donell wrote:

Any header needing compat with a libc includes libc-compat.h (per the 
documented way the model works). With this patch any included linux kernel
header that also includes libc-compat.h would immediately define all 
the __UAPI_DEF_* constants to 1 as-if it had defined those structures, 
but it has not.

For example, with these two patches applied, the inclusion of linux/if.h
would define __UAPI_DEF_XATTR to 1, but linux/if.h has not defined
XATTR_CREATE or other constants, so a subsequent inclusion sys/xattrs.h
from userspace would _not_ define XATTR_CREATE because __UAPI_DEF_XATTR set
to 1 indicates the kernel has.

I don't want to read into the model you are proposing and would rather you
document the semantics clearly so we can all see what you mean.

What about moving the code from libc-comapt.h into the specific header
files? This way including linux/if.h would not have an impact on
__UAPI_DEF_XATTR, because this is defined in linux/xattr.h. We would
still have a problem when the specific Linux header file gets included
before the libc header file, but at least musl does not support this anyway.

Hauke