core: introduce CGroupIOLimitType enums

Currently, there are two cgroup IO limits, bandwidth max for read and write,
and they are hard-coded in various places.  This is fine for two limits but IO
is expected to grow more limits - low, high and max limits for bandwidth and
IOPS - and hard-coding each limit won't make sense.

This patch replaces hard-coded limits with an array indexed by
CGroupIOLimitType and accompanying string and default value tables so that new
limits can be added trivially.

src/basic/cgroup-util.c

@@ -2269,6 +2269,18 @@ int cg_weight_parse(const char *s, uint64_t *ret) {
         return 0;
 }
 
+const uint64_t cgroup_io_limit_defaults[_CGROUP_IO_LIMIT_TYPE_MAX] = {
+        [CGROUP_IO_RBPS_MAX]    = CGROUP_LIMIT_MAX,
+        [CGROUP_IO_WBPS_MAX]    = CGROUP_LIMIT_MAX,
+};
+
+static const char* const cgroup_io_limit_type_table[_CGROUP_IO_LIMIT_TYPE_MAX] = {
+        [CGROUP_IO_RBPS_MAX]    = "IOReadBandwidthMax",
+        [CGROUP_IO_WBPS_MAX]    = "IOWriteBandwidthMax",
+};
+
+DEFINE_STRING_TABLE_LOOKUP(cgroup_io_limit_type, CGroupIOLimitType);
+
 int cg_cpu_shares_parse(const char *s, uint64_t *ret) {
         uint64_t u;
         int r;

src/basic/cgroup-util.h

@@ -72,6 +72,20 @@ static inline bool CGROUP_WEIGHT_IS_OK(uint64_t x) {
             (x >= CGROUP_WEIGHT_MIN && x <= CGROUP_WEIGHT_MAX);
 }
 
+/* IO limits on unified hierarchy */
+typedef enum CGroupIOLimitType {
+        CGROUP_IO_RBPS_MAX,
+        CGROUP_IO_WBPS_MAX,
+
+        _CGROUP_IO_LIMIT_TYPE_MAX,
+        _CGROUP_IO_LIMIT_TYPE_INVALID = -1
+} CGroupIOLimitType;
+
+extern const uint64_t cgroup_io_limit_defaults[_CGROUP_IO_LIMIT_TYPE_MAX];
+
+const char* cgroup_io_limit_type_to_string(CGroupIOLimitType t) _const_;
+CGroupIOLimitType cgroup_io_limit_type_from_string(const char *s) _pure_;
+
 /* Special values for the cpu.shares attribute */
 #define CGROUP_CPU_SHARES_INVALID ((uint64_t) -1)
 #define CGROUP_CPU_SHARES_MIN UINT64_C(2)