Add pkg/kmsg

This very simple program reads from `/dev/kmsg` and logs the output.

Signed-off-by: David Scott <dave.scott@docker.com>

docs/logging.md

@@ -88,8 +88,6 @@ conds
   socket could be created to keep syslog compatibility, e.g. by using
   https://github.com/mcuadros/go-syslog. Processes that require syslog should
   then be able to log directly to memlogd.
-- Kernel messages not read on startup yet (but can be captured with
-  `logwrite dmesg`)
 - Currently no direct external hooks exposed - but options available that
   could be added. Should also be possible to pipe output to e.g. `oklog`
   from `logread` (https://github.com/oklog/oklog)

pkg/kmsg/Dockerfile

@@ -0,0 +1,14 @@
+FROM linuxkit/alpine:6264e5b39af8eb1da7ffa4c05a7ccc597da01197 AS mirror
+
+RUN apk add --no-cache go musl-dev linux-headers
+ENV GOPATH=/go PATH=$PATH:/go/bin
+
+COPY .  /go/src/kmsg/
+RUN go-compile.sh /go/src/kmsg
+
+FROM scratch
+ENTRYPOINT []
+CMD []
+WORKDIR /
+COPY --from=mirror /go/bin/kmsg /usr/bin/kmsg
+CMD ["/usr/bin/kmsg"]

pkg/kmsg/build.yml

@@ -0,0 +1,6 @@
+image: kmsg
+config:
+  binds:
+    - /dev/kmsg:/dev/kmsg
+  capabilities:
+    - CAP_SYSLOG

pkg/kmsg/main.go

@@ -0,0 +1,25 @@
+package main
+
+// Log the kernel log buffer (from /dev/kmsg)
+
+import (
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/euank/go-kmsg-parser/kmsgparser"
+)
+
+func main() {
+	parser, err := kmsgparser.NewParser()
+	if err != nil {
+		log.Fatalf("unable to create parser: %v", err)
+	}
+	defer parser.Close()
+
+	kmsg := parser.Parse()
+
+	for msg := range kmsg {
+		fmt.Printf("(%d) - %s: %s", msg.SequenceNumber, msg.Timestamp.Format(time.RFC3339Nano), msg.Message)
+	}
+}

pkg/kmsg/vendor.conf

@@ -0,0 +1 @@
+github.com/euank/go-kmsg-parser 5ba4d492e455a77d25dcf0d2c4acc9f2afebef4e