enhacement to mdmfs

Hello,

I've recently shot my foot with mdmfs. Of course it was a pilot error but 
the funcioanility I was looking for might be usefull.

I want to mount vnode-backed md(4) on boot without formatting it (e.g. for a 
jail). Is it possible with current boot scripts?

I wrote a simple patch to mdmfs so such md disk can be put in /etc/fstab. It 
adds '-K' option do mdmfs(8) to Keep contents. The line to attach such disk 
in fstab looks like this:

md       /jail        mfs     rw,-K,-F=/var/jailfile 0 0

Comments welcome. If people find it usefull I'd like to have it commited. I 
can fill the PR with enhancement request.

Patch attached.

-- 
Michal Mertl




Index: mdmfs.8
===================================================================
RCS file: /home/fcvs/cvs/src/sbin/mdmfs/mdmfs.8,v
retrieving revision 1.20
diff -u -3 -r1.20 mdmfs.8
--- mdmfs.8	17 May 2004 08:35:41 -0000	1.20
+++ mdmfs.8	30 Nov 2004 10:56:22 -0000
_at__at_ -36,7 +36,7 _at__at_
 driver
 .Sh SYNOPSIS
 .Nm
-.Op Fl DLlMNSUX
+.Op Fl DKLlMNSUX
 .Op Fl a Ar maxcontig
 .Op Fl b Ar block-size
 .Op Fl c Ar cylinders
_at__at_ -57,7 +57,7 _at__at_
 .Ar mount-point
 .Nm
 .Fl C
-.Op Fl lNU
+.Op Fl KlNU
 .Op Fl a Ar maxcontig
 .Op Fl b Ar block-size
 .Op Fl c Ar cylinders
_at__at_ -162,6 +162,12 _at__at_
 The fragment size of the file system in bytes.
 .It Fl i Ar bytes
 Number of bytes per inode.
+.It Fl K
+Preserve contents of vnode-backed
+.Pq Dv MD_VNODE
+memory disk.
+Must be used in conjunction with
+.Fl F .
 .It Fl l
 Enable multilabel MAC on the new file system.
 .It Fl L
Index: mdmfs.c
===================================================================
RCS file: /home/fcvs/cvs/src/sbin/mdmfs/mdmfs.c,v
retrieving revision 1.20
diff -u -3 -r1.20 mdmfs.c
--- mdmfs.c	17 May 2004 07:07:20 -0000	1.20
+++ mdmfs.c	30 Nov 2004 10:51:56 -0000
_at__at_ -89,7 +89,7 _at__at_
 	    *mount_arg;
 	enum md_types mdtype;		/* The type of our memory disk. */
 	bool have_mdtype;
-	bool detach, softdep, autounit;
+	bool detach, softdep, autounit, keepdata;
 	char *mtpoint, *unitstr;
 	char *p;
 	int ch;
_at__at_ -119,7 +119,7 _at__at_
 		compat = true;
 
 	while ((ch = getopt(argc, argv,
-	    "a:b:Cc:Dd:e:F:f:hi:LlMm:Nn:O:o:p:Ss:t:Uv:w:X")) != -1)
+	    "a:b:Cc:Dd:e:F:f:hi:KLlMm:Nn:O:o:p:Ss:t:Uv:w:X")) != -1)
 		switch (ch) {
 		case 'a':
 			argappend(&newfs_arg, "-a %s", optarg);
_at__at_ -167,6 +167,8 _at__at_
 				usage();
 			loudsubs = true;
 			break;
+		case 'K':
+			keepdata = true;
 		case 'l':
 			argappend(&newfs_arg, "-l");
 			break;
_at__at_ -233,7 +235,6 _at__at_
 	argv += optind;
 	if (argc < 2)
 		usage();
-
 	/* Make compatibility assumptions. */
 	if (compat) {
 		mi.mi_mode = 01777;
_at__at_ -258,6 +259,11 _at__at_
 	mtpoint = argv[1];
 	if (!have_mdtype)
 		mdtype = MD_SWAP;
+
+	/* If we want to use vnode backed file and don't newfs it */
+	if (keepdata && mdtype != MD_VNODE)
+		err(1, "Must specify -F with -K");
+
 	if (softdep)
 		argappend(&newfs_arg, "-U");
 
_at__at_ -268,7 +274,8 _at__at_
 		do_mdconfig_attach_au(mdconfig_arg, mdtype);
 	else
 		do_mdconfig_attach(mdconfig_arg, mdtype);
-	do_newfs(newfs_arg);
+	if (!keepdata)
+		do_newfs(newfs_arg);
 	do_mount(mount_arg, mtpoint);
 	do_mtptsetup(mtpoint, &mi);
 
_at__at_ -665,13 +672,13 _at__at_
 		name = "mdmfs";
 	if (!compat)
 		fprintf(stderr,
-"usage: %s [-DLlMNSUX] [-a maxcontig [-b block-size] [-c cylinders]\n"
+"usage: %s [-DKLlMNSUX] [-a maxcontig [-b block-size] [-c cylinders]\n"
 "\t[-d rotdelay] [-e maxbpg] [-F file] [-f frag-size] [-i bytes]\n"
 "\t[-m percent-free] [-n rotational-positions] [-O optimization]\n"
 "\t[-o mount-options] [-p permissions] [-s size] [-w user:group]\n"
 "\tmd-device mount-point\n", name);
 	fprintf(stderr,
-"usage: %s -C [-lNU] [-a maxcontig] [-b block-size] [-c cylinders]\n"
+"usage: %s -C [-lKNU] [-a maxcontig] [-b block-size] [-c cylinders]\n"
 "\t[-d rotdelay] [-e maxbpg] [-F file] [-f frag-size] [-i bytes]\n"
 "\t[-m percent-free] [-n rotational-positions] [-O optimization]\n"
 "\t[-o mount-options] [-s size] md-device mount-point\n", name);