[3.4.3] linux/openat2.h: No such file or directory

[fda77]

Rsync is available to build with freetz-ng which is a firmware extension for avm router and other devices.
Hardware is mips, mipsel, arm, armeb, aarch64 and i686. Kernel versions are in range 2.6 - 5.4.
Currently there are 34 different toolchain combinations.
The kernel version could not be changed due to closed-source modules for dect, dsl, isdn, pots etc

3.4.2 compiled for all, 3.4.3 only for 2 of 34 toolchains due to missing "openat2.h", see: https://github.com/Freetz-NG/freetz-ng/actions/runs/26193880852

...
/home/builder/freetz-ng/toolchain/build/mips_gcc-13.4.0_uClibc-1.0.57-nptl_kernel-4.9/mips-linux-uclibc/bin/mips-linux-uclibc-gcc -I. -I. -march=34kc -mtune=34kc -msoft-float -Ofast -pipe -Wa,--trap -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Wl,-I/usr/lib/freetz/ld-uClibc.so.1 -DHAVE_CONFIG_H -Wall -W -Wno-unused-parameter  -c lib/sysacls.c -o lib/sysacls.o
/home/builder/freetz-ng/toolchain/build/mips_gcc-13.4.0_uClibc-1.0.57-nptl_kernel-4.9/mips-linux-uclibc/bin/mips-linux-uclibc-gcc -I. -I. -march=34kc -mtune=34kc -msoft-float -Ofast -pipe -Wa,--trap -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Wl,-I/usr/lib/freetz/ld-uClibc.so.1 -DHAVE_CONFIG_H -Wall -W -Wno-unused-parameter  -c lib/sysxattrs.c -o lib/sysxattrs.o
syscall.c:38:10: fatal error: linux/openat2.h: No such file or directory
   38 | #include <linux/openat2.h>
      |          ^~~~~~~~~~~~~~~~~
compilation terminated.

I "fixed" this problem with a #undef __linux__ which reverts 4fa7156

[fda77]

After my patch 32 of 34 can be compiled again: https://github.com/Freetz-NG/freetz-ng/actions/runs/26224316960

Please add some automatic fallback if the kernel has no openat2.h file

---

Unrelated to this issue

The 2 failing are missing "AT_SYMLINK_NOFOLLOW":

error: 'AT_SYMLINK_NOFOLLOW' undeclared (first use in this function)

[kirchwitz]

rsync 3.4.3 simply assumes without any further checks that every Linux must have openat2. Source code does not compile here on several older regular Linux systems. It basically limits rsync to systems with Linux kernel 5.6+. I guess that's not what was intended. :-)