Expand statfs man page a little and include in build.bash

Documentation/MANPAGE-STATFS.md

@@ -5,26 +5,78 @@
 NAME
 ====
 
-statfs - dump the statfs information for PATH to console in JSON format
+statfs - dump the statfs(2) information for PATH to console in JSON format.
 
 SYNOPSIS
 ========
 
-#### Examine encrypted file/directory
 statfs PATH
 
 DESCRIPTION
 ===========
 
-There are no options to this command.
+The statfs(2) system call returns information about a mounted filesystem
+in a `statfs_t` structure. This tool dumps this information in JSON format.
+It is developed as part of gocryptfs and written in Go.
+
+The `statfs_t` structure is architecture-dependent. On amd64 it looks like this:
+
+```
+type Statfs_t struct {
+	Type   int64
+	Bsize  int64
+	Blocks uint64
+	Bfree  uint64
+	Bavail uint64
+	Files  uint64
+	Ffree  uint64
+	Fsid   struct {
+		Val [2]int32
+	}
+	Namelen int64
+	Frsize  int64
+	Flags   int64
+	Spare   [4]int64
+}
+```
+
+See the statfs(2) man page for the meaning of these fields, and note
+that the field names here are acc. to the Go `golang.org/x/sys/unix`
+naming convention, and slightly different than in C.
 
 EXAMPLES
 ========
 
-Examine a directory entry:
+Get the statfs(2) information for /tmp:
 
-	statfs myfs/mCXnISiv7nEmyc0glGuhTQ
+```
+$ statfs /tmp
+{
+	"Type": 16914836,
+	"Bsize": 4096,
+	"Blocks": 3067428,
+	"Bfree": 3067411,
+	"Bavail": 3067411,
+	"Files": 3067428,
+	"Ffree": 3067381,
+	"Fsid": {
+		"Val": [
+			0,
+			0
+		]
+	},
+	"Namelen": 255,
+	"Frsize": 4096,
+	"Flags": 38,
+	"Spare": [
+		0,
+		0,
+		0,
+		0
+	]
+}
+```
 
 SEE ALSO
 ========
-gocryptfs(1) gocryptfs-xray(1)
+statfs(2) gocryptfs(1)

build.bash

@@ -87,10 +87,11 @@ if [[ -n ${LDFLAGS:-} ]] ; then
 	GO_LDFLAGS="$GO_LDFLAGS \"-extldflags=$LDFLAGS\""
 fi
 
-# Actual "go build" call
+# Actual "go build" call for gocryptfs
 go build "-ldflags=$GO_LDFLAGS" "-gcflags=$TRIM" "-asmflags=$TRIM" "$@"
-
+# Additional binaries
 (cd gocryptfs-xray; go build "-ldflags=$GO_LDFLAGS" "-gcflags=$TRIM" "-asmflags=$TRIM" "$@")
+(cd contrib/statfs; go build "-ldflags=$GO_LDFLAGS" "-gcflags=$TRIM" "-asmflags=$TRIM" "$@")
 
 ./gocryptfs -version
 

contrib/statfs/statfs.go

@@ -5,7 +5,8 @@ import (
 	"flag"
 	"fmt"
 	"os"
-	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
 const (
@@ -23,8 +24,8 @@ func main() {
 		flag.Usage()
 	}
 	path := flag.Arg(0)
-	var st syscall.Statfs_t
-	err := syscall.Statfs(path, &st)
+	var st unix.Statfs_t
+	err := unix.Statfs(path, &st)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "statfs syscall returned error: %v\n", err)
 		os.Exit(2)