status: use partuuid-based path in mkfs instruction

fixes https://github.com/gokrazy/gokrazy/issues/12

assets/overview.tmpl

@@ -64,7 +64,13 @@ unaccounted
 <h2>storage</h2>
 
 {{ if eq .PermAvail 0 }}
+
+{{ if ne .PARTUUID "" }}
+No permanent storage mounted. To create a filesystem for permanent storage, plug the SD card into a Linux computer and use <code>mkfs.ext4 /dev/disk/by-partuuid/{{ .PARTUUID }}-04</code>.
+{{ else }}
 No permanent storage mounted. To create a filesystem for permanent storage, plug the SD card into a Linux computer and, if your SD card is <code>/dev/sdb</code>, use <code>mkfs.ext4 /dev/sdb4</code>.
+{{ end }}
+
 {{ else }}
 <strong>{{ .PermDev }}</strong>: {{ gigabytes .PermTotal }} total, {{ gigabytes .PermUsed }} used, {{ gigabytes .PermAvail }} avail<br>
 {{ end }}

go.mod

@@ -14,3 +14,5 @@ require (
 	golang.org/x/sys v0.0.0-20200406155108-e3b113bbe6a4
 	rsc.io/goversion v1.2.0
 )
+
+replace github.com/gokrazy/internal => /home/stream/gohack/github.com/gokrazy/internal

status.go

@@ -231,6 +231,7 @@ func initStatus(services []*service) {
 			Meminfo        map[string]int64
 			Hostname       string
 			Model          string
+			PARTUUID       string
 		}{
 			Services:       services,
 			PermDev:        rootdev.Partition(rootdev.Perm),
@@ -243,6 +244,7 @@ func initStatus(services []*service) {
 			Meminfo:        parseMeminfo(),
 			Hostname:       hostname,
 			Model:          model,
+			PARTUUID:       rootdev.PARTUUID(),
 		}); err != nil {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return