configurable scan parallelism based on hdd or sdd

backend/system/disktype_linux.go

@@ -0,0 +1,96 @@
+//go:build linux
+
+package system
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+var errNoBlockDevice = errors.New(
+	"no matching block device found",
+)
+
+// IsRotationalDisk reports whether the block device backing the
+// given path is a rotational (spinning) disk.  Detection uses the
+// Linux sysfs interface at /sys/block/<dev>/queue/rotational.
+// Returns false on any error (assumes SSD).
+func IsRotationalDisk(path string) bool {
+	dev, err := deviceForPath(path)
+	if err != nil {
+		return false
+	}
+
+	rotational, err := os.ReadFile(
+		filepath.Join(
+			"/sys/block", dev, "queue", "rotational",
+		),
+	)
+	if err != nil {
+		return false
+	}
+
+	return strings.TrimSpace(string(rotational)) == "1"
+}
+
+// deviceForPath resolves a filesystem path to its underlying block
+// device name (e.g. "sda") by matching the device major:minor
+// from stat(2) against /sys/block/ entries.
+func deviceForPath(path string) (string, error) {
+	var st syscall.Stat_t
+	if err := syscall.Stat(path, &st); err != nil {
+		return "", fmt.Errorf(
+			"could not stat path: %w", err,
+		)
+	}
+
+	// Extract major and minor device numbers.
+	major := (st.Dev >> 8) & 0xff
+	minor := st.Dev & 0xff
+
+	// Scan /sys/block/ for a matching device.
+	entries, err := os.ReadDir("/sys/block")
+	if err != nil {
+		return "", fmt.Errorf(
+			"could not read /sys/block: %w", err,
+		)
+	}
+
+	majorStr := strconv.FormatUint(major, 10)
+	devStr := majorStr + ":" +
+		strconv.FormatUint(minor, 10)
+
+	for _, entry := range entries {
+		devFile := filepath.Join(
+			"/sys/block", entry.Name(), "dev",
+		)
+
+		data, err := os.ReadFile(devFile)
+		if err != nil {
+			continue
+		}
+
+		content := strings.TrimSpace(string(data))
+
+		if content == devStr {
+			return entry.Name(), nil
+		}
+
+		// The filesystem might be on a partition (e.g. sda1)
+		// whose parent block device is sda.  Check if the
+		// major number matches.
+		parts := strings.SplitN(content, ":", 2)
+		if len(parts) == 2 && parts[0] == majorStr {
+			return entry.Name(), nil
+		}
+	}
+
+	return "", fmt.Errorf(
+		"%w for %s", errNoBlockDevice, devStr,
+	)
+}

backend/system/disktype_other.go

@@ -0,0 +1,10 @@
+//go:build !linux
+
+package system
+
+// IsRotationalDisk reports whether the block device backing the
+// given path is a rotational (spinning) disk.  On non-Linux
+// platforms this always returns false (assumes SSD).
+func IsRotationalDisk(_ string) bool {
+	return false
+}