Created student weenix repository

1 files changed, 62 insertions, 0 deletions

diff --git a/kernel/proc/fork.c b/kernel/proc/fork.c
new file mode 100644
index 0000000..358b891
--- /dev/null
+++ b/kernel/proc/fork.c
@@ -0,0 +1,62 @@
+#include "errno.h"
+#include "globals.h"
+#include "types.h"
+
+#include "util/debug.h"
+#include "util/string.h"
+
+#include "mm/mm.h"
+#include "mm/mman.h"
+#include "mm/pframe.h"
+#include "mm/tlb.h"
+
+#include "fs/vnode.h"
+
+#include "vm/shadow.h"
+
+#include "api/exec.h"
+
+/* Pushes the appropriate things onto the kernel stack of a newly forked thread
+ * so that it can begin execution in userland_entry.
+ * regs: registers the new thread should have on execution
+ * kstack: location of the new thread's kernel stack
+ * Returns the new stack pointer on success. */
+static uintptr_t fork_setup_stack(const regs_t *regs, void *kstack)
+{
+    /* Pointer argument and dummy return address, and userland dummy return
+     * address */
+    uint64_t rsp =
+        ((uint64_t)kstack) + DEFAULT_STACK_SIZE - (sizeof(regs_t) + 16);
+    memcpy((void *)(rsp + 8), regs, sizeof(regs_t)); /* Copy over struct */
+    return rsp;
+}
+
+/*
+ * This function implements the fork(2) system call.
+ *
+ * TODO:
+ * 1) Use proc_create() and kthread_clone() to set up a new process and thread. If
+ *    either fails, perform any appropriate cleanup.
+ * 2) Finish any initialization work for the new process and thread.
+ * 3) Fix the values of the registers and the rest of the kthread's ctx. 
+ *    Some registers can be accessed from the cloned kthread's context (see the context_t 
+ *    and kthread_t structs for more details):
+ *    a) We want the child process to also enter userland execution. 
+ *       For this, the instruction pointer should point to userland_entry (see exec.c).
+ *    b) Remember that the only difference between the parent and child processes 
+ *       is the return value of fork(). This value is returned in the RAX register, 
+ *       and the return value should be 0 for the child. The parent's return value would 
+ *       be the process id of the newly created child process. 
+ *    c) Before the process begins execution in userland_entry, 
+ *       we need to push all registers onto the kernel stack of the kthread. 
+ *       Use fork_setup_stack to do this, and set RSP accordingly. 
+ *    d) Use pt_unmap_range and tlb_flush_all on the parent in advance of
+ *       copy-on-write.
+ * 5) Prepare the child process to be run on the CPU.
+ * 6) Return the child's process id to the parent.
+ */
+long do_fork(struct regs *regs)
+{
+    NOT_YET_IMPLEMENTED("VM: ***none***");
+    return -1;
+}