exec: allow passing arbitrary path names to blkio cgroup attributes

If a device node is specified, then adjust the bandwidth/weight of it,
otherwise find the backing block device of the file system the path
refers to and adjust its bandwidth/weight.

src/load-fragment.c

@@ -1843,6 +1843,7 @@ int config_parse_unit_device_allow(const char *filename, unsigned line, const ch
 static int blkio_map(const char *controller, const char *name, const char *value, char **ret) {
         struct stat st;
         char **l;
+        dev_t d;
 
         assert(controller);
         assert(name);
@@ -1861,13 +1862,23 @@ static int blkio_map(const char *controller, const char *name, const char *value
                 return -errno;
         }
 
-        if (!S_ISBLK(st.st_mode)) {
-                log_warning("%s is not a block device.", l[0]);
+        if (S_ISBLK(st.st_mode))
+                d = st.st_rdev;
+        else if (major(st.st_dev) != 0) {
+                /* If this is not a device node then find the block
+                 * device this file is stored on */
+                d = st.st_dev;
+
+                /* If this is a partition, try to get the originating
+                 * block device */
+                block_get_whole_disk(d, &d);
+        } else {
+                log_warning("%s is not a block device and file system block device cannot be determined or is not local.", l[0]);
                 strv_free(l);
                 return -ENODEV;
         }
 
-        if (asprintf(ret, "%u:%u %s", major(st.st_rdev), minor(st.st_rdev), l[1]) < 0) {
+        if (asprintf(ret, "%u:%u %s", major(d), minor(d), l[1]) < 0) {
                 strv_free(l);
                 return -ENOMEM;
         }
@@ -1907,7 +1918,7 @@ int config_parse_unit_blkio_weight(const char *filename, unsigned line, const ch
                 weight = l[1];
         }
 
-        if (device && !path_startswith(device, "/dev/")) {
+        if (device && !path_is_absolute(device)) {
                 log_error("[%s:%u] Failed to parse block device node value, ignoring: %s", filename, line, rvalue);
                 strv_free(l);
                 return 0;
@@ -1965,7 +1976,7 @@ int config_parse_unit_blkio_bandwidth(const char *filename, unsigned line, const
                 return 0;
         }
 
-        if (!path_startswith(l[0], "/dev/")) {
+        if (!path_is_absolute(l[0])) {
                 log_error("[%s:%u] Failed to parse block device node value, ignoring: %s", filename, line, rvalue);
                 strv_free(l);
                 return 0;

src/util.c

@@ -5614,6 +5614,67 @@ bool is_main_thread(void) {
         return cached > 0;
 }
 
+int block_get_whole_disk(dev_t d, dev_t *ret) {
+        char *p, *s;
+        int r;
+        unsigned n, m;
+
+        assert(ret);
+
+        /* If it has a queue this is good enough for us */
+        if (asprintf(&p, "/sys/dev/block/%u:%u/queue", major(d), minor(d)) < 0)
+                return -ENOMEM;
+
+        r = access(p, F_OK);
+        free(p);
+
+        if (r >= 0) {
+                *ret = d;
+                return 0;
+        }
+
+        /* If it is a partition find the originating device */
+        if (asprintf(&p, "/sys/dev/block/%u:%u/partition", major(d), minor(d)) < 0)
+                return -ENOMEM;
+
+        r = access(p, F_OK);
+        free(p);
+
+        if (r < 0)
+                return -ENOENT;
+
+        /* Get parent dev_t */
+        if (asprintf(&p, "/sys/dev/block/%u:%u/../dev", major(d), minor(d)) < 0)
+                return -ENOMEM;
+
+        r = read_one_line_file(p, &s);
+        free(p);
+
+        if (r < 0)
+                return r;
+
+        r = sscanf(s, "%u:%u", &m, &n);
+        free(s);
+
+        if (r != 2)
+                return -EINVAL;
+
+        /* Only return this if it is really good enough for us. */
+        if (asprintf(&p, "/sys/dev/block/%u:%u/queue", m, n) < 0)
+                return -ENOMEM;
+
+        r = access(p, F_OK);
+        free(p);
+
+        if (r >= 0) {
+                *ret = makedev(m, n);
+                return 0;
+        }
+
+        return -ENOENT;
+}
+
+
 static const char *const ioprio_class_table[] = {
         [IOPRIO_CLASS_NONE] = "none",
         [IOPRIO_CLASS_RT] = "realtime",

src/util.h

@@ -465,6 +465,8 @@ bool is_main_thread(void);
 
 bool in_charset(const char *s, const char* charset);
 
+int block_get_whole_disk(dev_t d, dev_t *ret);
+
 #define NULSTR_FOREACH(i, l)                                    \
         for ((i) = (l); (i) && *(i); (i) = strchr((i), 0)+1)