cgroup: update and fix parsing of "cgroup.subtree_control"
I was confused that strsep() was equivalent to strtok_r() in skipping over consecutive delimiters. strsep() just splits at the first occurrence of one of the delimiters which makes the parsing very inflexible, which makes allowing multiple whitespace chars as delimters kinda moot. Let's just be consistently strict and require list of tokens separated by spaces. This is what Documentation/cgroups/unified-hierarchy.txt describes too. Also, parsing may access beyond the end of the string if the string ends with spaces or is zero-length. Make sure it skips zero-length tokens. Note that this also ensures that the parser doesn't puke on multiple consecutive spaces. v2: Add zero-length token skipping. v3: Added missing space after "==". Spotted by Li. Signed-off-by: Tejun Heo <firstname.lastname@example.org> Acked-by: Li Zefan <email@example.com>