MPD 0.24 and openat2

[a-dekker]

I noticed MPD 0.24 now uses openat2, and there seems to be no fallback to openat. Does that mean kernels < 5.6 are no longer supported? Unfortunately in my case, I am bound to an ancient Android kernel (4.4.194).

[MaxKellermann]

What the actual problem you're having?

[a-dekker]

First of all, linux/openat2.h is not available in my environment (maybe not that strange given the kernel version). As a small test, I added the file manually and tried compiling, which leads to:

103.9 In file included from ../src/io/Open.cxx:10:
103.9 ../src/system/linux/openat2.h: In function 'int openat2(int, const char*, const open_how*, size_t)':
103.9 ../src/system/linux/openat2.h:16:17: error: '__NR_openat2' was not declared in this scope; did you mean '__openat_2'?
103.9    16 |  return syscall(__NR_openat2, dirfd, pathname, how, size);
103.9       |                 ^~~~~~~~~~~~
103.9       |                 __openat_2

[MaxKellermann]

Okay, so you havn't observed that MPD uses openat2, but you failed at building MPD. That shouldn't happen, and there should be a configure-time check whether your build environment supports this system call. I consider this a MPD bug.

[a-dekker]

Thanks for your swift commit aef1508 addressing this.

Sadly I encounter a next issue,

MPD/src/event/Loop.cxx

Line 360 in 19ccc1e

.tv_sec = std::chrono::ceil<std::chrono::duration<__kernel_time64_t>>(timeout).count(),

using kernel_time64_t

This looks to be added in kernel 5.10 (https://lwn.net/Articles/776427/), only kernel_time_t seems supported in my case (perhaps already 64-bit aware?).

To be clear, I do not expect you to support outdated kernels, but I thought I would let you know the further compiling outcome.

[MaxKellermann]

If you see this kind of problem, please write a bug report.

[a-dekker]

Sure, if you are willing to have a look at it I will write a bug report for this.