fix(overlays): backport smartctl_exporter Describe fix (upstream #329)

smartctl_exporter 0.14.0 derives Describe() from the devices it can read at startup. A device that only becomes readable later (an NVMe whose ACL arrives late, or an HDD waking from standby) then makes Collect() emit metrics with unregistered descriptors, so /metrics returns HTTP 500 and the whole scrape fails, hiding even the healthy disks.

Backport upstream PR #329, which makes Describe() send the full explicit descriptor set. Carry it as an overlay until smartctl_exporter 0.15.0 is released and packaged in nixpkgs.

Refs: https://github.com/prometheus-community/smartctl_exporter/pull/329

overlays/README.md

@@ -13,6 +13,9 @@ overlays/
 ├── default.nix            # Entrypoint for all overlays
 ├── computer-use-linux.nix # trycua/computer-use-linux package
 ├── cua-driver.nix         # trycua/cua driver (cua-driver) package
+├── smartctl-exporter/     # smartctl_exporter backport (upstream PR #329)
+│   ├── default.nix
+│   └── 329-explicit-descriptors.patch
 └── fcitx5/                # Chinese input method configuration
     ├── README.md
     ├── default.nix        # fcitx5 overlay definition
@@ -55,3 +58,6 @@ This overlay provides:
 
 - `computer-use-linux.nix`: packages `pkgs/computer-use-linux`.
 - `cua-driver.nix`: packages `pkgs/cua-driver` (used by the computer-use VMs).
+- `smartctl-exporter/`: patches `prometheus-smartctl-exporter` with upstream PR
+  [#329](https://github.com/prometheus-community/smartctl_exporter/pull/329) until smartctl_exporter
+  0.15.0 is released; see `overlays/smartctl-exporter/default.nix`.

overlays/smartctl-exporter/329-explicit-descriptors.patch

@@ -0,0 +1,50 @@
+diff --git a/main.go b/main.go
+index c5b138a..05a222e 100644
+--- a/main.go
++++ b/main.go
+@@ -57,7 +57,44 @@ type SMARTctlManagerCollector struct {
+ 
+ // Describe sends the super-set of all possible descriptors of metrics
+ func (i *SMARTctlManagerCollector) Describe(ch chan<- *prometheus.Desc) {
+-	prometheus.DescribeByCollect(i, ch)
++	ch <- metricSmartctlVersion
++	ch <- metricDeviceModel
++	ch <- metricDeviceCount
++	ch <- metricDeviceCapacityBlocks
++	ch <- metricDeviceCapacityBytes
++	ch <- metricDeviceTotalCapacityBytes
++	ch <- metricDeviceBlockSize
++	ch <- metricDeviceInterfaceSpeed
++	ch <- metricDeviceAttribute
++	ch <- metricDevicePowerOnSeconds
++	ch <- metricDeviceRotationRate
++	ch <- metricDeviceTemperature
++	ch <- metricDevicePowerCycleCount
++	ch <- metricDevicePercentageUsed
++	ch <- metricDeviceAvailableSpare
++	ch <- metricDeviceAvailableSpareThreshold
++	ch <- metricDeviceCriticalWarning
++	ch <- metricDeviceMediaErrors
++	ch <- metricDeviceNumErrLogEntries
++	ch <- metricDeviceBytesRead
++	ch <- metricDeviceBytesWritten
++	ch <- metricDeviceSmartStatus
++	ch <- metricDeviceExitStatus
++	ch <- metricDeviceState
++	ch <- metricDeviceStatistics
++	ch <- metricDeviceErrorLogCount
++	ch <- metricDeviceSelfTestLogCount
++	ch <- metricDeviceSelfTestLogErrorCount
++	ch <- metricDeviceERCSeconds
++	ch <- metricSCSIGrownDefectList
++	ch <- metricReadErrorsCorrectedByRereadsRewrites
++	ch <- metricReadErrorsCorrectedByEccFast
++	ch <- metricReadErrorsCorrectedByEccDelayed
++	ch <- metricReadTotalUncorrectedErrors
++	ch <- metricWriteErrorsCorrectedByRereadsRewrites
++	ch <- metricWriteErrorsCorrectedByEccFast
++	ch <- metricWriteErrorsCorrectedByEccDelayed
++	ch <- metricWriteTotalUncorrectedErrors
+ }
+ 
+ // Collect is called by the Prometheus registry when collecting metrics.

overlays/smartctl-exporter/default.nix

@@ -0,0 +1,15 @@
+# smartctl_exporter 0.14.0 derives `Describe()` from the devices it can read at
+# startup, so when a device only becomes readable later (an NVMe whose ACL
+# arrives late, or an HDD waking from standby) `Collect()` emits metrics whose
+# descriptors were never registered and `/metrics` starts returning HTTP 500,
+# which fails the whole scrape and hides even the healthy disks.
+#
+# Backport of upstream PR #329: `Describe()` now sends the full, explicit
+# descriptor set. Drop this overlay once smartctl_exporter 0.15.0 is released
+# and packaged in nixpkgs:
+#   https://github.com/prometheus-community/smartctl_exporter/pull/329
+_: _final: prev: {
+  prometheus-smartctl-exporter = prev.prometheus-smartctl-exporter.overrideAttrs (prevAttrs: {
+    patches = (prevAttrs.patches or [ ]) ++ [ ./329-explicit-descriptors.patch ];
+  });
+}