From 080151261b0993b888e4f5f822f2c86a47e0075e Mon Sep 17 00:00:00 2001
From: Matthias Kruk <m@m10k.eu>
Date: Wed, 30 Oct 2019 17:14:20 +0900
Subject: [PATCH] Add implementation of process_fork(), modify process_create()
 so that it can be used to fork a running process

---
 kernel/core/process.c    | 75 ++++++++++++++++++++++++++++++++++++++++
 kernel/include/process.h |  4 +++
 2 files changed, 79 insertions(+)

diff --git a/kernel/core/process.c b/kernel/core/process.c
index 8f70ec9..306e9be 100644
--- a/kernel/core/process.c
+++ b/kernel/core/process.c
@@ -9,6 +9,27 @@
 #include "fd.h"
 #include "sched.h"
 
+/* FIXME: Remove struct stack_frame from process.c */
+struct stack_frame {
+	u32_t cr3;
+	u32_t ds;
+	u32_t edi;
+	u32_t esi;
+	u32_t ebp;
+	u32_t esp;
+	u32_t ebx;
+	u32_t edx;
+	u32_t ecx;
+	u32_t eax;
+	u32_t intn;
+	u32_t error;
+	u32_t eip;
+	u32_t cs;
+	u32_t eflags;
+	u32_t prevesp;
+	u32_t ss;
+} __attribute__((packed));
+
 enum procstate {
 	PROC_STATE_INIT = 0,
 	PROC_STATE_READY,
@@ -20,6 +41,7 @@ struct process {
 	struct task    *p_tasks;
 	u32_t          p_privl;
 	pid_t          p_id;
+	pid_t          p_pid;
 
 	struct {
 		struct cxmsg *msg;
@@ -81,13 +103,17 @@ static inline int DQ(process_t *p)
 	return(ret_val);
 }
 
+void* task_get_eip3(void);
+
 int process_create(process_t **dst, pid_t pid, u32_t ppl, void *entry)
 {
 	int ret_val;
 	process_t *proc;
+	pid_t ppid;
 
 	ret_val = -ENOMEM;
 	proc = NULL;
+	ppid = 1;
 
 	/* was a specific pid requested? */
 	if(pid != PID_ANY) {
@@ -105,6 +131,16 @@ int process_create(process_t **dst, pid_t pid, u32_t ppl, void *entry)
 		}
 	}
 
+	if(entry == PROC_ENTRY_FORK ||
+	   entry == PROC_ENTRY_VFORK) {
+	    task_t *ctask;
+
+		/* inherit the ppl from the current task, in the case of fork and vfork */
+		ctask = task_get_current();
+		ppl = ctask->t_privl;
+		ppid = ctask->t_pid;
+	}
+
 	proc = kmalloc(sizeof(*proc));
 
 	if(proc) {
@@ -130,6 +166,7 @@ int process_create(process_t **dst, pid_t pid, u32_t ppl, void *entry)
 		}
 
 		proc->p_privl = ppl;
+		proc->p_pid = ppid;
 
 		if(pid == PID_ANY) {
 			/* no specific pid requested */
@@ -138,6 +175,27 @@ int process_create(process_t **dst, pid_t pid, u32_t ppl, void *entry)
 			proc->p_id = pid;
 		}
 
+		if(entry == PROC_ENTRY_FORK ||
+		   entry == PROC_ENTRY_VFORK) {
+			struct stack_frame *stack0;
+			task_t *ctask;
+
+			ctask = task_get_current();
+
+			/*
+			 * In the case of fork() and vfork() we have to get the address that the
+			 * interrupt is supposed to return to. The stack that the address was pushed
+			 * onto is located at ctask->t_kstack.
+			 */
+
+			stack0 = ((struct stack_frame*)(ctask->t_kstack + CONFIG_KERNEL_STACK_SIZE)) - 1;
+
+			entry = (void*)stack0->eip;
+			dbg_printf("entry = 0x%08x\n", (u32_t)entry);
+
+			for(;;);
+		}
+
 		task_prepare(proc->p_tasks, (u32_t)pdbr, (u32_t)entry,
 					 (u32_t)kstack + CONFIG_KERNEL_STACK_SIZE,
 					 (u32_t)ustack + CONFIG_USER_STACK_SIZE, ppl);
@@ -473,3 +531,20 @@ int process_exit(process_t *proc, int status)
 
 	return(ret_val);
 }
+
+int process_fork(int v)
+{
+	process_t *proc;
+	int ret_val;
+
+	proc = process_get_current();
+	ret_val = -EFAULT;
+
+	if(proc) {
+		process_t *nproc;
+
+		ret_val = process_create(&nproc, PID_ANY, proc->p_privl, PROC_ENTRY_FORK);
+	}
+
+	return(ret_val);
+}
diff --git a/kernel/include/process.h b/kernel/include/process.h
index 4c3baf3..480e2e0 100644
--- a/kernel/include/process.h
+++ b/kernel/include/process.h
@@ -22,6 +22,9 @@
 #include <corax/types.h>
 #include <corax/ipc.h>
 
+#define PROC_ENTRY_FORK  ((void*)0)
+#define PROC_ENTRY_VFORK ((void*)1)
+
 typedef struct process process_t;
 
 int process_create(process_t**, pid_t, u32_t, void*);
@@ -47,5 +50,6 @@ int           process_signal(pid_t);
 void*         process_get_tasks(process_t*);
 pid_t         process_get_id(process_t*);
 int           process_exit(process_t*, int);
+int           process_fork(int);
 
 #endif /* __PROCESS_H */
-- 
2.47.3