Re: [PATCH v9] y2038: Introduce the __ASSUME_TIME64_SYSCALLS define

[Zack Weinberg <zackw at panix dot com>]

On Tue, Aug 27, 2019 at 1:35 PM Alistair Francis
<alistair.francis@wdc.com> wrote:
> From: Lukasz Majewski <lukma@denx.de>
...

Thanks for tackling this revision.  I think it's much clearer now what
the flag means.  I would like to suggest some further improvements to
the wording of the comment and the commit message.

The commit message is largely redundant to the comment.  I think all
you need to say in the commit message is:

# Add __ASSUME_TIME64_SYSCALLS macro to linux/kernel-features.h.
#
# __ASSUME_TIME64_SYSCALLS will be defined (with value 1) if the Linux
# kernel can be assumed to provide a complete set of system calls that
# process 64-bit time_t.
#
# __ASSUME_TIME64_SYSCALLS does not indicate whether time_t is
# actually 64 bits (that's __TIMEBITS) and also does not indicate
# whether the 64-bit time_t system calls have "time64" suffixes on
# their names.

And then the comment should be something like this:

# /* Support for 64-bit time_t in the system call interface.
#
#    This flag is always true for Linux 5.1 and later.  Prior to that
#    version, it is true only for some CPU architectures and ABIs:
#
#    - __WORDSIZE == 64 - all supported architectures where pointers
#      are 64 bits also have always had 64-bit time_t.
#
#    - __WORDSIZE == 32 && __SYSCALL_WORDSIZE == 64 - this describes
#      only one supported configuration, x86's 'x32' subarchitecture,
#      where pointers are 32 bits but time_t has always been 64 bits.
#
#    For architectures where __WORDSIZE == 32 && __SYSCALL_WORDSIZE != 64,
#    glibc supports both 32-bit time_t (__TIMESIZE == 32) and 64-bit time_t
#    (__TIMESIZE == 64).  Independent of this, when __ASSUME_TIME64_SYSCALLS
#    is defined, glibc uses only the 64-bit time_t system calls; conversions
#    occur in user space.  When __ASSUME_TIME64_SYSCALLS is *not* defined,
#    glibc will attempt to use the 64-bit time_t system calls but will fall
#    back to the 32-bit system calls if they are not available.
#
#    Because of this, __ASSUME_TIME64_SYSCALLS being defined does not
#    mean that __TIMESIZE is 64, and __TIMESIZE being equal to 64 does
#    not mean that __ASSUME_TIME64_SYSCALLS is defined.  All four
#    cases are possible.  */

I think that gets everything important.  Neither the commit message
nor the comment needs to list all the new system calls.

zw