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

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

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))

sys/dev/md/md.c

@@ -226,6 +226,7 @@ struct md_s {
 	/* MD_VNODE related fields */
 	struct vnode *vnode;
 	char file[PATH_MAX];
+	char label[PATH_MAX];
 	struct ucred *cred;
 
 	/* MD_SWAP related fields */
@@ -1645,6 +1646,11 @@ xmdctlioctl(struct cdev *dev, u_long cmd, caddr_t addr, int flags, struct thread
 		}
 		if (sc == NULL)
 			return (error);
+		if (mdio->md_label != NULL)
+			error = copyinstr(mdio->md_label, sc->label,
+			    sizeof(sc->label), NULL);
+		if (error != 0)
+			goto err_after_new;
 		if (mdio->md_options & MD_AUTOUNIT)
 			mdio->md_unit = sc->unit;
 		sc->mediasize = mdio->md_mediasize;
@@ -1676,6 +1682,7 @@ xmdctlioctl(struct cdev *dev, u_long cmd, caddr_t addr, int flags, struct thread
 			error = mdcreate_null(sc, mdio, td);
 			break;
 		}
+err_after_new:
 		if (error != 0) {
 			mddestroy(sc, td);
 			return (error);
@@ -1721,6 +1728,11 @@ xmdctlioctl(struct cdev *dev, u_long cmd, caddr_t addr, int flags, struct thread
 		mdio->md_options = sc->flags;
 		mdio->md_mediasize = sc->mediasize;
 		mdio->md_sectorsize = sc->sectorsize;
+		error = 0;
+		if (mdio->md_label != NULL) {
+			error = copyout(sc->label, mdio->md_label,
+			    strlen(sc->label) + 1);
+		}
 		if (sc->type == MD_VNODE ||
 		    (sc->type == MD_PRELOAD && mdio->md_file != NULL))
 			error = copyout(sc->file, mdio->md_file,
@@ -1873,6 +1885,7 @@ g_md_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp,
 			if ((mp->type == MD_VNODE && mp->vnode != NULL) ||
 			    (mp->type == MD_PRELOAD && mp->file[0] != '\0'))
 				sbuf_printf(sb, " file %s", mp->file);
+			sbuf_printf(sb, " label %s", mp->label);
 		} else {
 			sbuf_printf(sb, "%s<unit>%d</unit>\n", indent,
 			    mp->unit);
@@ -1897,6 +1910,9 @@ g_md_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp,
 				g_conf_printf_escaped(sb, "%s", mp->file);
 				sbuf_printf(sb, "</file>\n");
 			}
+			sbuf_printf(sb, "%s<label>", indent);
+			g_conf_printf_escaped(sb, "%s", mp->label);
+			sbuf_printf(sb, "</label>\n");
 		}
 	}
 }

sys/sys/mdioctl.h

@@ -49,7 +49,7 @@ enum md_types {MD_MALLOC, MD_PRELOAD, MD_VNODE, MD_SWAP, MD_NULL};
  * Ioctl definitions for memory disk pseudo-device.
  */
 
-#define MDNPAD		97
+#define MDNPAD		96
 struct md_ioctl {
 	unsigned	md_version;	/* Structure layout version */
 	unsigned	md_unit;	/* unit number */
@@ -61,6 +61,7 @@ struct md_ioctl {
 	u_int64_t	md_base;	/* base address */
 	int		md_fwheads;	/* firmware heads */
 	int		md_fwsectors;	/* firmware sectors */
+	char		*md_label;	/* label of the device */
 	int		md_pad[MDNPAD];	/* padding for future ideas */
 };