From 897625ff9b8d718555baa408b05398ad178d986e Mon Sep 17 00:00:00 2001
From: fgergo <fgergo@gmail.com>
Date: Sun, 7 Jan 2024 17:06:26 +0100
Subject: [PATCH] mntgen: import mntgen(4) from Plan 9

new file:   man/man4/mntgen.4
new file:   src/cmd/mntgen.c
---
 man/man4/mntgen.4 |  32 ++++++
 src/cmd/mntgen.c  | 256 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 288 insertions(+)
 create mode 100644 man/man4/mntgen.4
 create mode 100644 src/cmd/mntgen.c

diff --git a/man/man4/mntgen.4 b/man/man4/mntgen.4
new file mode 100644
index 00000000..af3b7568
--- /dev/null
+++ b/man/man4/mntgen.4
@@ -0,0 +1,32 @@
+.TH MNTGEN 4
+.SH NAME
+mntgen  \-  automatically generate mount points for file systems
+.SH SYNOPSIS
+.B mntgen
+[
+.B -s
+.I service
+]
+[
+.I mnt
+]
+.SH DESCRIPTION
+.I Mntgen
+mounts itself on
+.I mnt
+(default
+.BR /n )
+after the current contents,
+creating subdirectories on demand as they are accessed.
+It is intended to supply mount points automatically.
+.PP
+The
+.B -s
+option causes
+.I mntgen
+to post a 9P
+.I service \fR
+file.
+.SH SOURCE
+.B \*9/src/cmd/mntgen.c
+
diff --git a/src/cmd/mntgen.c b/src/cmd/mntgen.c
new file mode 100644
index 00000000..19483a79
--- /dev/null
+++ b/src/cmd/mntgen.c
@@ -0,0 +1,256 @@
+#include <u.h>
+#include <libc.h>
+#include <fcall.h>
+#include <thread.h>
+#include <9p.h>
+#include <mp.h>
+#include <libsec.h>
+
+static void
+usage(void)
+{
+	fprint(2, "mntgen [-s srvname] [mtpt]\n");
+	threadexits("usage");
+}
+
+ulong time0;
+
+typedef struct Tab Tab;
+struct Tab
+{
+	char *name;
+	vlong qid;
+	ulong time;
+	int ref;
+};
+
+Tab *tab;
+int ntab;
+int mtab;
+
+static Tab*
+findtab(vlong path)
+{
+	int i;
+
+	for(i=0; i<ntab; i++)
+		if(tab[i].qid == path)
+			return &tab[i];
+	return nil;
+}
+
+static vlong
+hash(char *name)
+{
+	vlong digest[MD5dlen / sizeof(vlong) + 1];
+	md5((uchar *)name, strlen(name), (uchar *)digest, nil);
+	return digest[0] & ((1ULL<<48)-1);
+}
+
+static void
+fsopen(Req *r)
+{
+	if(r->ifcall.mode != OREAD)
+		respond(r, "permission denied");
+	else
+		respond(r, nil);
+}
+
+static int
+dirgen(int i, Dir *d, void* v)
+{
+	USED(v);
+
+	if(i >= ntab)
+		return -1;
+	memset(d, 0, sizeof *d);
+	d->qid.type = QTDIR;
+	d->uid = estrdup9p("sys");
+	d->gid = estrdup9p("sys");
+	d->mode = DMDIR|0555;
+	d->length = 0;
+	if(i == -1){
+		d->name = estrdup9p("/");
+		d->atime = d->mtime = time0;
+	}else{
+		d->qid.path = tab[i].qid;
+		d->name = estrdup9p(tab[i].name);
+		d->atime = d->mtime = tab[i].time;
+	}
+	return 0;
+}
+
+static void
+fsread(Req *r)
+{
+	if(r->fid->qid.path == 0)
+		dirread9p(r, dirgen, nil);
+	else
+		r->ofcall.count = 0;
+	respond(r, nil);
+}
+
+static void
+fsstat(Req *r)
+{
+	Tab *t;
+	vlong qid;
+
+	qid = r->fid->qid.path;
+	if(qid == 0)
+		dirgen(-1, &r->d, nil);
+	else{
+		if((t = findtab(qid)) == nil){
+			respond(r, "path not found ( ??? )");
+			return;
+		}
+		dirgen(t-tab, &r->d, nil);
+	}
+	respond(r, nil);
+}
+
+static char*
+fswalk1(Fid *fid, char *name, void* v)
+{
+	int i;
+	Tab *t;
+	vlong h;
+
+	USED(v);
+
+	if(fid->qid.path != 0){
+		/* nothing in child directory */
+		if(strcmp(name, "..") == 0){
+			if((t = findtab(fid->qid.path)) != nil)
+				t->ref--;
+			fid->qid.path = 0;
+			return nil;
+		}
+		return "path not found";
+	}
+	/* root */
+	if(strcmp(name, "..") == 0)
+		return nil;
+	for(i=0; i<ntab; i++)
+		if(strcmp(tab[i].name, name) == 0){
+			tab[i].ref++;
+			fid->qid.path = tab[i].qid;
+			return nil;
+		}
+	h = hash(name);
+	if(findtab(h) != nil)
+		return "hash collision";
+
+	/* create it */
+	if(ntab == mtab){
+		if(mtab == 0)
+			mtab = 16;
+		else
+			mtab *= 2;
+		tab = erealloc9p(tab, sizeof(tab[0])*mtab);
+	}
+	tab[ntab].qid = h;
+	fid->qid.path = tab[ntab].qid;
+	tab[ntab].name = estrdup9p(name);
+	tab[ntab].time = time(0);
+	tab[ntab].ref = 1;
+	ntab++;
+
+	return nil;
+}
+
+static char*
+fsclone(Fid *fid, Fid* v, void* w)
+{
+	USED(v);
+	USED(w);
+
+	Tab *t;
+
+	if((t = findtab(fid->qid.path)) != nil)
+		t->ref++;
+	return nil;
+}
+
+static void
+fswalk(Req *r)
+{
+	walkandclone(r, fswalk1, fsclone, nil);
+}
+
+static void
+fsclunk(Fid *fid)
+{
+	Tab *t;
+	vlong qid;
+
+	qid = fid->qid.path;
+	if(qid == 0)
+		return;
+	if((t = findtab(qid)) == nil){
+		fprint(2, "warning: cannot find %llux\n", qid);
+		return;
+	}
+	if(--t->ref == 0){
+		free(t->name);
+		tab[t-tab] = tab[--ntab];
+	}else if(t->ref < 0)
+		fprint(2, "warning: negative ref count for %s\n", t->name);
+}
+
+static void
+fsattach(Req *r)
+{
+	char *spec;
+
+	spec = r->ifcall.aname;
+	if(spec && spec[0]){
+		respond(r, "invalid attach specifier");
+		return;
+	}
+	
+	r->ofcall.qid = (Qid){0, 0, QTDIR};
+	r->fid->qid = r->ofcall.qid;
+	respond(r, nil);
+}
+
+Srv fs=
+{
+.attach=	fsattach,
+.open=	fsopen,
+.read=	fsread,
+.stat=	fsstat,
+.walk=	fswalk,
+.destroyfid=	fsclunk
+};
+
+int
+threadmaybackground(void)
+{
+	return 1;
+}
+
+void
+threadmain(int argc, char *argv[])
+{
+	char *service;
+
+	time0 = time(0);
+	service = nil;
+	ARGBEGIN{
+	case 'D':
+		chatty9p++;
+		break;
+	case 's':
+		service = EARGF(usage());
+		break;
+	default:
+		usage();
+	}ARGEND
+
+	if(argc > 1)
+		usage();
+	threadpostmountsrv(&fs, service, argc ? argv[0] : "/n", MAFTER);
+	threadexits(nil);
+}
+