plumber: remove $plumbsrv, add optional srvname, usage check

Plumber both posts a service to /srv and sets a $plumbsrv environment
variable.  Our libplumb no longer uses $plumbsrv and nothing else
does.  It's a silly hack;  rc doesn't update /env immediately, and
scripts, which for instance set up subrios, cannot rely on it to
clean up the plumber at the end.

Instead, add the option to specify a srvname, actually check for some
common errors and print a usage string.

Thanks to Ori for input and a preliminary patch.

1 files changed, 4 insertions, 3 deletions

diff --git a/sys/src/cmd/plumb/fsys.c b/sys/src/cmd/plumb/fsys.c
index 378543139..db3ff6b54 100644
--- a/sys/src/cmd/plumb/fsys.c
+++ b/sys/src/cmd/plumb/fsys.c
@@ -218,9 +218,10 @@ startfsys(void)
 	clock = getclock();
 	if(cexecpipe(&mntfd, &srvfd) < 0)
 		error("can't create pipe: %r");
-	sprint(srvfile, "/srv/plumb.%s.%d", user, getpid());
-	if(putenv("plumbsrv", srvfile) < 0)
-		error("can't write $plumbsrv: %r");
+	if(srvname == nil)
+		snprint(srvfile, sizeof(srvfile), "/srv/plumb.%s.%d", user, getpid());
+	else
+		snprint(srvfile, sizeof(srvfile), "/srv/%s", srvname);
 	fd = create(srvfile, OWRITE|OCEXEC|ORCLOSE, 0600);
 	if(fd < 0)
 		error("can't create /srv file: %r");