Add ability to label md(4) devices.

This feature comes from the fact that we rely memory-backed md(4)
in our build process heavily. However, if the build goes haywire
the allocated resources (i.e. swap and memory-backed md(4)'s) need
to be purged. It is extremely useful to have ability to attach
arbitrary labels to each of the virtual disks so that they can
be identified and GC'ed if neecessary.

MFC after:	4 weeks
Differential Revision:	https://reviews.freebsd.org/D10457

2 files changed, 26 insertions, 9 deletions

diff --git a/sbin/mdconfig/mdconfig.8 b/sbin/mdconfig/mdconfig.8
index a437e40d58ec..cf05d8f43efb 100644
--- a/sbin/mdconfig/mdconfig.8
+++ b/sbin/mdconfig/mdconfig.8
@@ -37,7 +37,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd October 10, 2015
+.Dd August 28, 2017
 .Dt MDCONFIG 8
 .Os
 .Sh NAME
@@ -55,6 +55,7 @@
 .Op Fl u Ar unit
 .Op Fl x Ar sectors/track
 .Op Fl y Ar heads/cylinder
+.Op Fl L Ar label
 .Nm
 .Fl d
 .Fl u Ar unit
@@ -189,6 +190,12 @@ and
 options can be used to specify a synthetic geometry.
 This is useful for constructing bootable images for later download to
 other devices.
+.It Fl L Ar label
+Associate a label (arbitrary string) with the new memory disk.
+The label can then be inspected with
+.Bd -literal -offset indent
+.Nm Fl l v
+.Ed
 .It Fl o Oo Cm no Oc Ns Ar option
 Set or reset options.
 .Bl -tag -width indent
diff --git a/sbin/mdconfig/mdconfig.c b/sbin/mdconfig/mdconfig.c
index 12c2a82c44d7..a76af2c7fdb0 100644
--- a/sbin/mdconfig/mdconfig.c
+++ b/sbin/mdconfig/mdconfig.c
@@ -79,7 +79,7 @@ usage(void)
 
 	fprintf(stderr,
 "usage: mdconfig -a -t type [-n] [-o [no]option] ... [-f file]\n"
-"                [-s size] [-S sectorsize] [-u unit]\n"
+"                [-s size] [-S sectorsize] [-u unit] [-L label]\n"
 "                [-x sectors/track] [-y heads/cylinder]\n"
 "       mdconfig -d -u unit [-o [no]force]\n"
 "       mdconfig -r -u unit -s size [-o [no]force]\n"
@@ -102,15 +102,17 @@ main(int argc, char **argv)
 
 	bzero(&mdio, sizeof(mdio));
 	mdio.md_file = malloc(PATH_MAX);
-	if (mdio.md_file == NULL)
+	mdio.md_label = malloc(PATH_MAX);
+	if (mdio.md_file == NULL || mdio.md_label == NULL)
 		err(1, "could not allocate memory");
 	vflag = 0;
 	bzero(mdio.md_file, PATH_MAX);
+	bzero(mdio.md_label, PATH_MAX);
 
 	if (argc == 1)
 		usage();
 
-	while ((ch = getopt(argc, argv, "ab:df:lno:rs:S:t:u:vx:y:")) != -1) {
+	while ((ch = getopt(argc, argv, "ab:df:lno:rs:S:t:u:vx:y:L:")) != -1) {
 		switch (ch) {
 		case 'a':
 			if (action != UNSET && action != ATTACH)
@@ -243,6 +245,9 @@ main(int argc, char **argv)
 		case 'y':
 			mdio.md_fwheads = strtoul(optarg, &p, 0);
 			break;
+		case 'L':
+			strlcpy(mdio.md_label, optarg, PATH_MAX);
+			break;
 		default:
 			usage();
 		}
@@ -422,7 +427,8 @@ md_list(const char *units, int opt, const char *fflag)
 	struct gclass *gcl;
 	void *sq;
 	int retcode, ffound, ufound;
-	char *type, *file, *length;
+	char *length;
+	const char *type, *file, *label;
 
 	type = file = length = NULL;
 
@@ -477,10 +483,14 @@ md_list(const char *units, int opt, const char *fflag)
 				printf("\t%s\t", type);
 				if (length != NULL)
 					md_prthumanval(length);
-				if (file != NULL) {
-					printf("\t%s", file);
-					file = NULL;
-				}
+				if (file == NULL)
+					file = "-";
+				printf("\t%s", file);
+				file = NULL;
+				label = geom_config_get(gc, "label");
+				if (label == NULL)
+					label = "";
+				printf("\t%s", label);
 			}
 			opt |= OPT_DONE;
 			if ((opt & OPT_LIST) && !(opt & OPT_VERBOSE))