v0.5.5: protocol detection, SAT fallback, device_overrides, --discover

- Use --scan-open on first poll for accurate protocol detection (falls
  back to --scan if unsupported)
- Auto-retry SCSI drives with -d sat on open failure; cache working
  protocol for subsequent polls
- Add device_overrides config for Synology /dev/sata* and RAID paths
- Add --discover diagnostic flag with platform detection and optional
  config write

Fixes #16 (QNAP SAT), #17 (Synology device paths)

Author: DAB-LABS

CHANGELOG.md

@@ -2,6 +2,23 @@
 
 All notable changes to SMART Sniffer are documented here.
 
+## v0.5.5 -- 2026-04-24
+
+Agent-only release. No integration or installer changes required.
+
+Addresses issues [#16](https://github.com/DAB-LABS/smart-sniffer/issues/16) (QNAP SATA drives misreported as SCSI) and [#17](https://github.com/DAB-LABS/smart-sniffer/issues/17) (Synology `/dev/sata*` paths not discovered by scan).
+
+### Added
+- **NAS protocol auto-detection on startup** -- the agent now uses `smartctl --scan-open` on its first scan cycle instead of `--scan`. This opens device handles and gives more accurate protocol detection, which fixes QNAP HBAs that report SATA drives as SCSI. Subsequent cycles revert to regular `--scan` to avoid waking sleeping drives.
+- **SAT fallback for misreported SCSI drives** -- if a drive is reported as SCSI but smartctl cannot read it, the agent automatically retries with `-d sat` (SCSI-to-ATA Translation). If that works, the agent uses SAT for that drive going forward and logs it once. No config required -- QNAP users affected by #16 should see this pick up their drives automatically.
+- **`device_overrides` config option** -- for drives that need an explicit protocol the agent cannot auto-detect (Synology `/dev/sata*` paths, RAID controllers with custom `-d` syntax), you can now list them in `config.yaml`. Overridden devices are treated as first-class drives even if they are not found by `--scan`.
+- **`--discover` diagnostic flag** -- run `smartha-agent --discover` to probe every drive, test protocol detection, check SAT fallback, and print a clear summary of what the agent will see at runtime. On Synology, it also probes `/dev/sata1` through `/dev/sata8`. If any drives need `device_overrides`, it offers to write the config for you. Useful for support: paste the output into a GitHub issue and we can diagnose protocol problems without asking for manual smartctl runs.
+
+### Upgrade Notes
+- **Agent update only.** Replace the binary or re-run the installer. No integration update, config migration, or installer re-run is required.
+- **QNAP users affected by #16:** update the agent -- no config change needed. The SAT fallback handles this automatically.
+- **Synology users affected by #17:** update the agent and run `smartha-agent --discover` to generate the `device_overrides` block for your config. Restart the agent after writing the config.
+
 ## v0.5.4 -- 2026-04-21
 
 Integration-only release. No agent changes required.

agent/config.go

@@ -20,6 +20,13 @@ type FilesystemConfig struct {
 	Device string `yaml:"device"`
 }
 
+// DeviceOverride allows manual protocol specification for drives that
+// auto-detection cannot handle (Synology paths, RAID controllers, etc.).
+type DeviceOverride struct {
+	Device   string `yaml:"device"`
+	Protocol string `yaml:"protocol"`
+}
+
 // Config holds all agent configuration. Values are resolved with this
 // precedence: CLI flags > config file > defaults.
 type Config struct {
@@ -31,6 +38,9 @@ type Config struct {
 	MDNSName           string             `yaml:"mdns_name"`           // custom mDNS instance name (default: smartha-<hostname>)
 	Filesystems        []FilesystemConfig `yaml:"filesystems"`         // empty = disk usage monitoring disabled
 	StandbyMode        string             `yaml:"standby_mode"`        // never, standby, sleep, idle (default: never)
+	DeviceOverrides    []DeviceOverride   `yaml:"device_overrides"`    // manual protocol overrides per device path
+	Discover           bool               `yaml:"-"`                   // set by --discover flag; not read from config file
+	NoWrite            bool               `yaml:"-"`                   // set by --no-write flag; skips config write in discover mode
 }
 
 // defaultConfig returns sane defaults.
@@ -70,6 +80,8 @@ func LoadConfig() (*Config, error) {
 	noMDNS := flag.Bool("no-mdns", false, "Disable mDNS/Zeroconf service advertisement")
 	advIface := flag.String("interface", "", "Restrict mDNS advertisement to this network interface")
 	mdnsName := flag.String("mdns-name", "", "Custom mDNS instance name (default: smartha-<hostname>)")
+	discover := flag.Bool("discover", false, "Probe drives and detect protocols (diagnostic tool)")
+	noWrite := flag.Bool("no-write", false, "With --discover: print proposed overrides but do not write config")
 	flag.Parse()
 
 	// --- Attempt to load config.yaml ---
@@ -116,6 +128,12 @@ func LoadConfig() (*Config, error) {
 	if *mdnsName != "" {
 		cfg.MDNSName = *mdnsName
 	}
+	if *discover {
+		cfg.Discover = true
+	}
+	if *noWrite {
+		cfg.NoWrite = true
+	}
 
 	// Sanity checks
 	if cfg.Port < 1 || cfg.Port > 65535 {
@@ -136,6 +154,16 @@ func LoadConfig() (*Config, error) {
 		return nil, fmt.Errorf("invalid standby_mode %q (must be never, standby, sleep, or idle)", cfg.StandbyMode)
 	}
 
+	// Validate device_overrides
+	for i, ov := range cfg.DeviceOverrides {
+		if ov.Device == "" {
+			return nil, fmt.Errorf("device_overrides[%d]: device path is required", i)
+		}
+		if ov.Protocol == "" {
+			return nil, fmt.Errorf("device_overrides[%d]: protocol is required for %s", i, ov.Device)
+		}
+	}
+
 	return &cfg, nil
 }