Add go-fuse logger

soci-snapshotter-gprc overrides the default logger to be a logrus logger
with debug as the write level. If the snapshotter is invoked with
`--log-level debug`, then logs from e.g. `log.PrinLn` are visibile.

go-fuse uses this logging method to output a complete transaction of
fuse operations keeping track of each request/response with a unique id.
The ID is only unique within a single server, so trying to parse the
logs is ambiguous since you don't know which server a response
corresponds to.

go-fuse recently added support for per-server loggers. This change uses
that functionality to add the layer digest to the logs from each fuse
server so request/response pairs can be unambiguously matched.

It also changes the log level of go-fuse logs to trace since there
really is no debug reason for enabling them.

Signed-off-by: Kern Walster <[email protected]>

fs/fs.go

@@ -45,6 +45,7 @@ package fs
 import (
 	"context"
 	"fmt"
+	golog "log"
 	"os/exec"
 	"sync"
 	"syscall"
@@ -494,10 +495,16 @@ func (fs *filesystem) Mount(ctx context.Context, mountpoint string, labels map[s
 		NegativeTimeout: &fs.negativeTimeout,
 		NullPermissions: true,
 	})
+	// Pass in a logger to go-fuse with the layer digest
+	// The go-fuse logs are useful for tracing exactly what's happening at the fuse level.
+	logger := log.L.
+		WithField("layerDigest", labels[ctdsnapshotters.TargetLayerDigestLabel]).
+		WriterLevel(logrus.TraceLevel)
 	mountOpts := &fuse.MountOptions{
 		AllowOther: true,   // allow users other than root&mounter to access fs
 		FsName:     "soci", // name this filesystem as "soci"
 		Debug:      fs.debug,
+		Logger:     golog.New(logger, "", 0),
 	}
 	if _, err := exec.LookPath(fusermountBin); err == nil {
 		mountOpts.Options = []string{"suid"} // option for fusermount; allow setuid inside container