croup: expose IO accounting data per unit

This was the last kind of accounting still not exposed on for each unit.
Let's fix that.

Note that this is a relatively simplistic approach: we don't expose
per-device stats, but sum them all up, much like cgtop does. This kind
of metric is probably the most interesting for most usecases, and covers
the "systemctl status" output best. If we want per-device stats one day
we can of course always add that eventually.

1 files changed, 142 insertions, 3 deletions

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index 5bf6224e31..2bfa8df0cb 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -3178,6 +3178,127 @@ int unit_get_ip_accounting(
         return r;
 }
 
+static int unit_get_io_accounting_raw(Unit *u, uint64_t ret[static _CGROUP_IO_ACCOUNTING_METRIC_MAX]) {
+        static const char *const field_names[_CGROUP_IO_ACCOUNTING_METRIC_MAX] = {
+                [CGROUP_IO_READ_BYTES]       = "rbytes=",
+                [CGROUP_IO_WRITE_BYTES]      = "wbytes=",
+                [CGROUP_IO_READ_OPERATIONS]  = "rios=",
+                [CGROUP_IO_WRITE_OPERATIONS] = "wios=",
+        };
+        uint64_t acc[_CGROUP_IO_ACCOUNTING_METRIC_MAX] = {};
+        _cleanup_free_ char *path = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
+        int r;
+
+        assert(u);
+
+        if (!u->cgroup_path)
+                return -ENODATA;
+
+        if (unit_has_host_root_cgroup(u))
+                return -ENODATA; /* TODO: return useful data for the top-level cgroup */
+
+        r = cg_all_unified();
+        if (r < 0)
+                return r;
+        if (r == 0) /* TODO: support cgroupv1 */
+                return -ENODATA;
+
+        if (!FLAGS_SET(u->cgroup_realized_mask, CGROUP_MASK_IO))
+                return -ENODATA;
+
+        r = cg_get_path("io", u->cgroup_path, "io.stat", &path);
+        if (r < 0)
+                return r;
+
+        f = fopen(path, "re");
+        if (!f)
+                return -errno;
+
+        for (;;) {
+                _cleanup_free_ char *line = NULL;
+                const char *p;
+
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                p = line;
+                p += strcspn(p, WHITESPACE); /* Skip over device major/minor */
+                p += strspn(p, WHITESPACE);  /* Skip over following whitespace */
+
+                for (;;) {
+                        _cleanup_free_ char *word = NULL;
+
+                        r = extract_first_word(&p, &word, NULL, EXTRACT_RETAIN_ESCAPE);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                break;
+
+                        for (CGroupIOAccountingMetric i = 0; i < _CGROUP_IO_ACCOUNTING_METRIC_MAX; i++) {
+                                const char *x;
+
+                                x = startswith(word, field_names[i]);
+                                if (x) {
+                                        uint64_t w;
+
+                                        r = safe_atou64(x, &w);
+                                        if (r < 0)
+                                                return r;
+
+                                        /* Sum up the stats of all devices */
+                                        acc[i] += w;
+                                        break;
+                                }
+                        }
+                }
+        }
+
+        memcpy(ret, acc, sizeof(acc));
+        return 0;
+}
+
+int unit_get_io_accounting(
+                Unit *u,
+                CGroupIOAccountingMetric metric,
+                bool allow_cache,
+                uint64_t *ret) {
+
+        uint64_t raw[_CGROUP_IO_ACCOUNTING_METRIC_MAX];
+        int r;
+
+        /* Retrieve an IO account parameter. This will subtract the counter when the unit was started. */
+
+        if (!UNIT_CGROUP_BOOL(u, io_accounting))
+                return -ENODATA;
+
+        if (allow_cache && u->io_accounting_last[metric] != UINT64_MAX)
+                goto done;
+
+        r = unit_get_io_accounting_raw(u, raw);
+        if (r == -ENODATA && u->io_accounting_last[metric] != UINT64_MAX)
+                goto done;
+        if (r < 0)
+                return r;
+
+        for (CGroupIOAccountingMetric i = 0; i < _CGROUP_IO_ACCOUNTING_METRIC_MAX; i++) {
+                /* Saturated subtraction */
+                if (raw[i] > u->io_accounting_base[i])
+                        u->io_accounting_last[i] = raw[i] - u->io_accounting_base[i];
+                else
+                        u->io_accounting_last[i] = 0;
+        }
+
+done:
+        if (ret)
+                *ret = u->io_accounting_last[metric];
+
+        return 0;
+}
+
 int unit_reset_cpu_accounting(Unit *u) {
         int r;
 
@@ -3210,15 +3331,33 @@ int unit_reset_ip_accounting(Unit *u) {
         return r < 0 ? r : q;
 }
 
+int unit_reset_io_accounting(Unit *u) {
+        int r;
+
+        assert(u);
+
+        for (CGroupIOAccountingMetric i = 0; i < _CGROUP_IO_ACCOUNTING_METRIC_MAX; i++)
+                u->io_accounting_last[i] = UINT64_MAX;
+
+        r = unit_get_io_accounting_raw(u, u->io_accounting_base);
+        if (r < 0) {
+                zero(u->io_accounting_base);
+                return r;
+        }
+
+        return 0;
+}
+
 int unit_reset_accounting(Unit *u) {
-        int r, q;
+        int r, q, v;
 
         assert(u);
 
         r = unit_reset_cpu_accounting(u);
-        q = unit_reset_ip_accounting(u);
+        q = unit_reset_io_accounting(u);
+        v = unit_reset_ip_accounting(u);
 
-        return r < 0 ? r : q;
+        return r < 0 ? r : q < 0 ? q : v;
 }
 
 void unit_invalidate_cgroup(Unit *u, CGroupMask m) {