Fix: display online_cpus in compat REST API

Signed-off-by: Boaz Shuster <boaz.shuster.github@gmail.com>

libpod/stats_common.go

@@ -47,3 +47,8 @@ func (c *Container) GetContainerStats(previousStats *define.ContainerStats) (*de
 	}
 	return stats, nil
 }
+
+// GetOnlineCPUs returns the number of online CPUs as set in the container cpu-set using sched_getaffinity
+func GetOnlineCPUs(container *Container) (int, error) {
+	return getOnlineCPUs(container)
+}

libpod/stats_freebsd.go

@@ -147,3 +147,7 @@ func calculateBlockIO(stats *cgroups.Metrics) (read uint64, write uint64) {
 	}
 	return
 }
+
+func getOnlineCPUs(container *Container) (int, error) {
+	return 0, nil
+}

libpod/stats_linux.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/containers/common/pkg/cgroups"
 	"github.com/containers/podman/v4/libpod/define"
+	"golang.org/x/sys/unix"
 )
 
 // getPlatformContainerStats gets the platform-specific running stats
@@ -129,3 +130,18 @@ func calculateBlockIO(stats *runccgroup.Stats) (read uint64, write uint64) {
 	}
 	return
 }
+
+func getOnlineCPUs(container *Container) (int, error) {
+	ctrPID, err := container.PID()
+	if err != nil {
+		return -1, fmt.Errorf("failed to obtain Container %s PID: %w", container.Name(), err)
+	}
+	if ctrPID == 0 {
+		return ctrPID, define.ErrCtrStopped
+	}
+	var cpuSet unix.CPUSet
+	if err := unix.SchedGetaffinity(ctrPID, &cpuSet); err != nil {
+		return -1, fmt.Errorf("failed to obtain Container %s online cpus: %w", container.Name(), err)
+	}
+	return cpuSet.Count(), nil
+}

pkg/api/handlers/compat/containers_stats.go

@@ -80,6 +80,11 @@ func StatsContainer(w http.ResponseWriter, r *http.Request) {
 			ThrottlingData: docker.ThrottlingData{},
 		}
 	}
+	onlineCPUs, err := libpod.GetOnlineCPUs(ctnr)
+	if err != nil {
+		utils.InternalServerError(w, err)
+		return
+	}
 
 streamLabel: // A label to flatten the scope
 	select {
@@ -178,7 +183,7 @@ streamLabel: // A label to flatten the scope
 					},
 					CPU:         stats.CPU,
 					SystemUsage: systemUsage,
-					OnlineCPUs:  uint32(len(cgroupStat.CpuStats.CpuUsage.PercpuUsage)),
+					OnlineCPUs:  uint32(onlineCPUs),
 					ThrottlingData: docker.ThrottlingData{
 						Periods:          0,
 						ThrottledPeriods: 0,

test/apiv2/19-stats.at

@@ -0,0 +1,11 @@
+# -*- sh -*-
+#
+# test 'stats' endpoints
+#
+
+if root; then
+    podman run -dt --name container1 --cpuset-cpus=0 $IMAGE top &>/dev/null
+
+    # regression for https://github.com/containers/podman/issues/15754
+    t GET libpod/containers/container1/stats?stream=false 200 .cpu_stats.online_cpus=1
+fi