rtla: Replace get_nprocs_conf() with sysfs possible cpus

rtla uses get_nprocs_conf(), a standard libc routine, to retrieve the
total number of CPUs for the purpose of processing per-CPU data.

In some configurations, libc might return a different value than what is
seen by the kernel. To cover for this situation, replace the call to
get_nprocs_conf() with a newly added helper, get_possible_cpus().

get_possible_cpus() reads /sys/devices/system/cpu/possible and parses
the CPU list, identically to what libbpf_num_possible_cpus() does.
Additionally, it checks that the possible cpu list is zero-based and has
no holes by computing both the cpu count and the maximum cpu number.
Systems where /sys/.../cpu/possible is unreadable, is not zero-based,
or has holes, now report an error instead of crashing later due to unmet
assumptions.

Note that parse_cpu_set() cannot be used to parse
/sys/devices/system/cpu/possible, because it only supports CPU count of
1024 and lower. Higher CPU counts are not fully supported by rtla;
nr_cpus > 1024 is, though, so it has to be covered by the new
implementation in order to avoid a regression.

A new function, cpu_list_iterate(), is added to utils.c to contain the
cpu list parsing logic, which is now shared between the new function
get_possible_cpus() and the pre-existing parse_cpu_set().

Assisted-by: Claude:claude-opus-4-6
Link: https://lore.kernel.org/r/20260814135511.2207190-2-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

0 files changed, 0 insertions, 0 deletions