Retry exec commands on text file busy

This makes the plugin validation a bit more robust by retrying the
execution if the plugin is in text file busy state. This can happen if
we write the config and the plugin at once. To avoid such races we now
try up to 5 seconds for the plugin validation.

Signed-off-by: Sascha Grunert <sgrunert@suse.com>

pkg/invoke/raw_exec.go

@@ -21,6 +21,8 @@ import (
 	"fmt"
 	"io"
 	"os/exec"
+	"strings"
+	"time"
 
 	"github.com/containernetworking/cni/pkg/types"
 )
@@ -37,7 +39,24 @@ func (e *RawExec) ExecPlugin(ctx context.Context, pluginPath string, stdinData [
 	c.Stdin = bytes.NewBuffer(stdinData)
 	c.Stdout = stdout
 	c.Stderr = stderr
-	if err := c.Run(); err != nil {
+
+	// Retry the command on "text file busy" errors
+	for i := 0; i <= 5; i++ {
+		err := c.Run()
+
+		// Command succeeded
+		if err == nil {
+			break
+		}
+
+		// If the plugin is currently about to be written, then we wait a
+		// second and try it again
+		if strings.Contains(err.Error(), "text file busy") {
+			time.Sleep(time.Second)
+			continue
+		}
+
+		// All other errors except than the busy text file
 		return nil, e.pluginErr(err, stdout.Bytes(), stderr.Bytes())
 	}