Implement the spread policy for IRQ affinity distribution using a
topology-aware algorithm. The algorithm:
1. Discovers CPU topology from sysfs (NUMA node, package, die/L3, core)
2. Groups CPUs by L3 cache domain (die) with equidistant ordering
3. Round-robins across dies, spreading IRQs across the system
4. Uses first hyperthread of each core before second hyperthreads
5. Applies IRQ affinity via /proc/irq/<n>/smp_affinity
When there are more IRQs than CPUs, queues wrap around using round-robin.
Latest glibc uses _Generic to have strstr() and other functions return
const char* or char* based on whether the input is a const char* or a
char*. This causes build failures as we previously always expected a char*.
Let's fix the compilation failures and add our own macros similar to glibc's
to have string functions that return a mutable or const pointer depending on
the input.
Let's not leak details from src/shared and src/libsystemd into
src/basic, even though you can't actually do anything useful with
just forward declarations from src/shared.
The sd-forward.h header is put in src/libsystemd/sd-common as we
don't have a directory for shared internal headers for libsystemd
yet.
Let's also rename forward.h to basic-forward.h to keep things
self-explanatory.
Quentin Deslandes
Daan De Meyer
Lennart Poettering
Yu Watanabe
Zbigniew Jędrzejewski-Szmek