helpers: cpumask: add helper to convert a cpumask to string of cpu ra…

…nges.

In some cases (for example getting affinity of an irq), it is better
to have an easily understandable list of cpus corresonding to a given
cpumask.
This helper converts a given cpumask to string, such that the string
represents the range of CPUs that are present in the given mask.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>

drgn/helpers/linux/cpumask.py

@@ -60,3 +60,50 @@ def for_each_possible_cpu(prog: Program) -> Iterator[int]:
 def for_each_present_cpu(prog: Program) -> Iterator[int]:
     """Iterate over all present CPUs."""
     return _for_each_cpu_mask(prog, "__cpu_present_mask")
+
+
+def cpumask_to_cpulist(cpumask: Object) -> str:
+    """
+    Get list of CPUs, present in a cpumask.
+
+    :param cpumask: ``struct cpumask*``
+    :returns: list of CPUs as string
+    """
+    start = 0
+    end = 0
+    count = 1
+    cpu_range = str()
+    all_cpu_ranges = str()
+    cpulist = [cpu for cpu in for_each_cpu(cpumask)]
+
+    if len(cpulist) == 1:  # Just one CPU in mask
+        return str(cpulist[0])
+
+    for index, value in enumerate(cpulist):
+        if index < len(cpulist) - 1:
+            if cpulist[index + 1] > value + 1:
+                end = index
+                if count > 1:
+                    cpu_range = str(cpulist[start]) + "-" + str(cpulist[end])
+                else:
+                    cpu_range = str(cpulist[start])
+                start = end + 1
+                count = 1
+                if not len(all_cpu_ranges):
+                    all_cpu_ranges += cpu_range
+                else:
+                    all_cpu_ranges += ", " + cpu_range
+            else:
+                count += 1
+        else:
+            if count == index + 1:  # only one range
+                all_cpu_ranges = str(cpulist[start]) + "-" + str(cpulist[index])
+            else:
+                if cpulist[start] == cpulist[index]:  # only one element in last range
+                    all_cpu_ranges += ", " + str(cpulist[index])
+                else:  # more than 1 element in last range
+                    all_cpu_ranges += (
+                        ", " + str(cpulist[start]) + "-" + str(cpulist[index])
+                    )
+
+    return all_cpu_ranges