From 8ed3e74c3fa05fcbdd985fb3de59e9baee38f12f Mon Sep 17 00:00:00 2001
From: Giacomo Tesio <giacomo@tesio.it>
Date: Mon, 25 Dec 2017 13:13:09 +0100
Subject: [PATCH] libposix: fix setpgid: if the target process is already a
 group leader, do nothing

---
 sys/src/lib/posix/ids.c     | 8 +++++++-
 sys/src/lib/posix/posixly.c | 4 +++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/sys/src/lib/posix/ids.c b/sys/src/lib/posix/ids.c
index 4acf1fd..749867a 100644
--- a/sys/src/lib/posix/ids.c
+++ b/sys/src/lib/posix/ids.c
@@ -49,12 +49,14 @@ __libposix_sighelper_set_pgid(int target, int group)
 		long			raw;
 	} offset;
 	IntBuf buf;
+	long ret;
 
 	offset.request.command = PHSetProcessGroup;
 	offset.request.target = target;
 
 	buf.group = group;
-	return pwrite(*__libposix_devsignal, buf.raw, sizeof(buf.raw), offset.raw);
+	ret = pwrite(*__libposix_devsignal, buf.raw, sizeof(buf.raw), offset.raw);
+	return ret;
 }
 
 static int
@@ -77,11 +79,15 @@ CreateNewProcessGroup:
 		rfork(RFNOTEG);
 		return __libposix_sighelper_cmd(PHSetProcessGroup, mypid);
 	}
+	if(pid == 0)
+		pid = mypid;
 	ppid = get_ppid(pid);
 	if(ppid == -1 || pid != mypid && mypid != ppid){
 		*errnop = __libposix_get_errno(PosixESRCH);
 		return -1;
 	}
+	if(group == 0)
+		group = pid;
 	if(pid == group && pid == mypid)
 		goto CreateNewProcessGroup;
 
diff --git a/sys/src/lib/posix/posixly.c b/sys/src/lib/posix/posixly.c
index 64932a1..6d735ef 100644
--- a/sys/src/lib/posix/posixly.c
+++ b/sys/src/lib/posix/posixly.c
@@ -329,8 +329,10 @@ group_create(Process *leader)
 	ProcessGroup* g;
 	assert(leader != nil);
 
-	if((leader->flags & GroupLeader) || (leader->flags & SessionLeader))
+	if(leader->flags & SessionLeader)
 		return nil;	/* operation not permitted */
+	if(leader->group && leader->group->pgid == leader->pid)
+		return leader->group;	/* nothing to do */
 
 	g = mallocz(sizeof(ProcessGroup), 1);
 	if(g == nil)