From 0ed2f796d7723af8321f35d4ef5e6781ea41e36d Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Thu, 18 Aug 2022 14:11:31 +0200
Subject: syscall/fork: FORK_SHAREMEM for primitive "threads"

---
 src/kernel/proc.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

(limited to 'src/kernel/proc.c')

diff --git a/src/kernel/proc.c b/src/kernel/proc.c
index 2e765c7..906fc29 100644
--- a/src/kernel/proc.c
+++ b/src/kernel/proc.c
@@ -50,7 +50,17 @@ struct process *process_fork(struct process *parent, int flags) {
 	struct process *child = kmalloc(sizeof *child);
 	memset(child, 0, sizeof *child);
 
-	child->pages = pagedir_copy(parent->pages);
+	if (flags & FORK_SHAREMEM) {
+		if (!parent->pages_refcount) {
+			parent->pages_refcount = kmalloc(sizeof *parent->pages_refcount);
+			*parent->pages_refcount = 1;
+		}
+		*parent->pages_refcount += 1;
+		child->pages_refcount = parent->pages_refcount;
+		child->pages = parent->pages;
+	} else {
+		child->pages = pagedir_copy(parent->pages);
+	}
 	child->regs  = parent->regs;
 	child->state = parent->state;
 	assert(child->state == PS_RUNNING); // not copying the state union
@@ -152,7 +162,16 @@ void process_kill(struct process *p, int ret) {
 			p->execbuf.buf = NULL;
 		}
 
-		pagedir_free(p->pages);
+		if (p->pages_refcount) {
+			assert(*p->pages_refcount != 0);
+			*p->pages_refcount -= 1;
+			if (*p->pages_refcount == 0) {
+				kfree(p->pages_refcount);
+				pagedir_free(p->pages);
+			}
+		} else {
+			pagedir_free(p->pages);
+		}
 
 		// TODO VULN unbounded recursion
 		struct process *c2;
-- 
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