[system/process] Log pid in all cases (#187)

Return PID as well while returning errors. This helps with debugging.

metric/system/process/process.go

@@ -229,7 +229,7 @@ func (procStats *Stats) pidFill(pid int, filter bool) (ProcState, bool, error) {
 	// OS-specific entrypoint, get basic info so we can at least run matchProcess
 	status, err := GetInfoForPid(procStats.Hostfs, pid)
 	if err != nil {
-		return status, true, fmt.Errorf("GetInfoForPid: %w", err)
+		return status, true, fmt.Errorf("GetInfoForPid failed for pid %d: %w", pid, err)
 	}
 	if procStats.skipExtended {
 		return status, true, nil
@@ -250,7 +250,7 @@ func (procStats *Stats) pidFill(pid int, filter bool) (ProcState, bool, error) {
 	status, err = FillPidMetrics(procStats.Hostfs, pid, status, procStats.isWhitelistedEnvVar)
 	if err != nil {
 		if !errors.Is(err, NonFatalErr{}) {
-			return status, true, fmt.Errorf("FillPidMetrics: %w", err)
+			return status, true, fmt.Errorf("FillPidMetrics failed for PID %d: %w", pid, err)
 		}
 		wrappedErr = errors.Join(wrappedErr, fmt.Errorf("non-fatal error fetching PID metrics for %d, metrics are valid, but partial: %w", pid, err))
 		procStats.logger.Debugf(wrappedErr.Error())
@@ -282,7 +282,7 @@ func (procStats *Stats) pidFill(pid int, filter bool) (ProcState, bool, error) {
 
 	status, err = FillMetricsRequiringMoreAccess(pid, status)
 	if err != nil {
-		return status, true, fmt.Errorf("FillMetricsRequiringMoreAccess: %w", err)
+		return status, true, fmt.Errorf("FillMetricsRequiringMoreAccess failed for pid %d: %w", pid, err)
 	}
 
 	// Generate `status.Cmdline` here for compatibility because on Windows

metric/system/process/process_windows.go

@@ -102,7 +102,7 @@ func FetchNumThreads(pid int) (int, error) {
 
 	currentProcessHandle, err := syscall.GetCurrentProcess()
 	if err != nil {
-		return 0, fmt.Errorf("GetCurrentProcess failed: %w", err)
+		return 0, fmt.Errorf("GetCurrentProcess failed for PID %d: %w", pid, err)
 	}
 	// The pseudo handle need not be closed when it is no longer
 	// needed, calling CloseHandle has no effect.  Adding here to
@@ -114,7 +114,7 @@ func FetchNumThreads(pid int) (int, error) {
 	var snapshotHandle syscall.Handle
 	err = PssCaptureSnapshot(targetProcessHandle, PSSCaptureThreads, 0, &snapshotHandle)
 	if err != nil {
-		return 0, fmt.Errorf("PssCaptureSnapshot failed: %w", err)
+		return 0, fmt.Errorf("PssCaptureSnapshot failed for PID %d: %w", pid, err)
 	}
 
 	info := PssThreadInformation{}
@@ -189,28 +189,28 @@ func getProcArgs(pid int) ([]string, error) {
 		false,
 		uint32(pid))
 	if err != nil {
-		return nil, fmt.Errorf("OpenProcess failed: %w", err)
+		return nil, fmt.Errorf("OpenProcess failed for PID %d: %w", pid, err)
 	}
 	defer func() {
 		_ = syscall.CloseHandle(handle)
 	}()
 	pbi, err := windows.NtQueryProcessBasicInformation(handle)
 	if err != nil {
-		return nil, fmt.Errorf("NtQueryProcessBasicInformation failed: %w", err)
+		return nil, fmt.Errorf("NtQueryProcessBasicInformation failed for PID %d: %w", pid, err)
 	}
 
 	userProcParams, err := windows.GetUserProcessParams(handle, pbi)
 	if err != nil {
-		return nil, fmt.Errorf("GetUserProcessParams failed: %w", err)
+		return nil, fmt.Errorf("GetUserProcessParams failed for PID %d: %w", pid, err)
 	}
 	argsW, err := windows.ReadProcessUnicodeString(handle, &userProcParams.CommandLine)
 	if err != nil {
-		return nil, fmt.Errorf("ReadProcessUnicodeString failed: %w", err)
+		return nil, fmt.Errorf("ReadProcessUnicodeString failed for PID %d: %w", pid, err)
 	}
 
 	procList, err := windows.ByteSliceToStringSlice(argsW)
 	if err != nil {
-		return nil, fmt.Errorf("ByteSliceToStringSlice failed: %w", err)
+		return nil, fmt.Errorf("ByteSliceToStringSlice failed for PID %d: %w", pid, err)
 	}
 	return procList, nil
 }