--mount: support arbitrary mount-argument order

Support an arbitrary order in which arguments are specified to the
`--mount` flag.  Previously, Podman expected `type=...` to come
first which was breaking compatibility with Docker.

Note that this is the ground work to default to "volume" (again Docker
compat).  However, this will require some further massaging as we have
to assign a name.

Fixes: containers#7628
Signed-off-by: Valentin Rothberg <[email protected]>

cmd/podman/common/volumes.go

@@ -28,6 +28,7 @@ var (
 	errDuplicateDest = errors.Errorf("duplicate mount destination")
 	optionArgError   = errors.Errorf("must provide an argument for option")
 	noDestError      = errors.Errorf("must set volume destination")
+	errInvalidSyntax = errors.Errorf("incorrect mount format: should be --mount type=<bind|tmpfs|volume>,[src=<host-dir|volume-name>,]target=<ctr-dir>[,options]")
 )
 
 // Parse all volume-related options in the create config into a set of mounts
@@ -147,6 +148,27 @@ func parseVolumes(volumeFlag, mountFlag, tmpfsFlag []string, addReadOnlyTmpfs bo
 	return finalMounts, finalVolumes, finalOverlayVolume, nil
 }
 
+// findMountType parses the input and extracts the type of the mount type and
+// the remaining non-type tokens.
+func findMountType(input string) (mountType string, tokens []string, err error) {
+	// Split by comma, iterate over the slice and look for
+	// "type=$mountType". Everything else is appended to tokens.
+	found := false
+	for _, s := range strings.Split(input, ",") {
+		kv := strings.Split(s, "=")
+		if found || !(len(kv) == 2 && kv[0] == "type") {
+			tokens = append(tokens, s)
+			continue
+		}
+		mountType = kv[1]
+		found = true
+	}
+	if !found {
+		err = errInvalidSyntax
+	}
+	return
+}
+
 // getMounts takes user-provided input from the --mount flag and creates OCI
 // spec mounts and Libpod named volumes.
 // podman run --mount type=bind,src=/etc/resolv.conf,target=/etc/resolv.conf ...
@@ -156,25 +178,13 @@ func getMounts(mountFlag []string) (map[string]spec.Mount, map[string]*specgen.N
 	finalMounts := make(map[string]spec.Mount)
 	finalNamedVolumes := make(map[string]*specgen.NamedVolume)
 
-	errInvalidSyntax := errors.Errorf("incorrect mount format: should be --mount type=<bind|tmpfs|volume>,[src=<host-dir|volume-name>,]target=<ctr-dir>[,options]")
-
-	// TODO(vrothberg): the manual parsing can be replaced with a regular expression
-	//                  to allow a more robust parsing of the mount format and to give
-	//                  precise errors regarding supported format versus supported options.
 	for _, mount := range mountFlag {
-		arr := strings.SplitN(mount, ",", 2)
-		if len(arr) < 2 {
-			return nil, nil, errors.Wrapf(errInvalidSyntax, "%q", mount)
+		// TODO: Docker defaults to "volume" if no mount type is specified.
+		mountType, tokens, err := findMountType(mount)
+		if err != nil {
+			return nil, nil, err
 		}
-		kv := strings.Split(arr[0], "=")
-		// TODO: type is not explicitly required in Docker.
-		// If not specified, it defaults to "volume".
-		if len(kv) != 2 || kv[0] != "type" {
-			return nil, nil, errors.Wrapf(errInvalidSyntax, "%q", mount)
-		}
-
-		tokens := strings.Split(arr[1], ",")
-		switch kv[1] {
+		switch mountType {
 		case TypeBind:
 			mount, err := getBindMount(tokens)
 			if err != nil {
@@ -212,7 +222,7 @@ func getMounts(mountFlag []string) (map[string]spec.Mount, map[string]*specgen.N
 			}
 			finalNamedVolumes[volume.Dest] = volume
 		default:
-			return nil, nil, errors.Errorf("invalid filesystem type %q", kv[1])
+			return nil, nil, errors.Errorf("invalid filesystem type %q", mountType)
 		}
 	}