Lab 4

lib/Makefrag

@@ -10,6 +10,11 @@ LIB_SRCFILES :=		lib/console.c \
 			lib/string.c \
 			lib/syscall.c
 
+LIB_SRCFILES :=		$(LIB_SRCFILES) \
+			lib/pgfault.c \
+			lib/pfentry.S \
+			lib/fork.c \
+			lib/ipc.c
 
 
 

lib/console.c

@@ -18,7 +18,7 @@ getchar(void)
 	int r;
 	// sys_cgetc does not block, but getchar should.
 	while ((r = sys_cgetc()) == 0)
-		;
+		sys_yield();
 	return r;
 }
 

lib/fork.c

@@ -0,0 +1,90 @@
+// implement fork from user space
+
+#include <inc/string.h>
+#include <inc/lib.h>
+
+// PTE_COW marks copy-on-write page table entries.
+// It is one of the bits explicitly allocated to user processes (PTE_AVAIL).
+#define PTE_COW		0x800
+
+//
+// Custom page fault handler - if faulting page is copy-on-write,
+// map in our own private writable copy.
+//
+static void
+pgfault(struct UTrapframe *utf)
+{
+	void *addr = (void *) utf->utf_fault_va;
+	uint32_t err = utf->utf_err;
+	int r;
+
+	// Check that the faulting access was (1) a write, and (2) to a
+	// copy-on-write page.  If not, panic.
+	// Hint:
+	//   Use the read-only page table mappings at uvpt
+	//   (see <inc/memlayout.h>).
+
+	// LAB 4: Your code here.
+
+	// Allocate a new page, map it at a temporary location (PFTEMP),
+	// copy the data from the old page to the new page, then move the new
+	// page to the old page's address.
+	// Hint:
+	//   You should make three system calls.
+
+	// LAB 4: Your code here.
+
+	panic("pgfault not implemented");
+}
+
+//
+// Map our virtual page pn (address pn*PGSIZE) into the target envid
+// at the same virtual address.  If the page is writable or copy-on-write,
+// the new mapping must be created copy-on-write, and then our mapping must be
+// marked copy-on-write as well.  (Exercise: Why do we need to mark ours
+// copy-on-write again if it was already copy-on-write at the beginning of
+// this function?)
+//
+// Returns: 0 on success, < 0 on error.
+// It is also OK to panic on error.
+//
+static int
+duppage(envid_t envid, unsigned pn)
+{
+	int r;
+
+	// LAB 4: Your code here.
+	panic("duppage not implemented");
+	return 0;
+}
+
+//
+// User-level fork with copy-on-write.
+// Set up our page fault handler appropriately.
+// Create a child.
+// Copy our address space and page fault handler setup to the child.
+// Then mark the child as runnable and return.
+//
+// Returns: child's envid to the parent, 0 to the child, < 0 on error.
+// It is also OK to panic on error.
+//
+// Hint:
+//   Use uvpd, uvpt, and duppage.
+//   Remember to fix "thisenv" in the child process.
+//   Neither user exception stack should ever be marked copy-on-write,
+//   so you must allocate a new page for the child's user exception stack.
+//
+envid_t
+fork(void)
+{
+	// LAB 4: Your code here.
+	panic("fork not implemented");
+}
+
+// Challenge!
+int
+sfork(void)
+{
+	panic("sfork not implemented");
+	return -E_INVAL;
+}

lib/ipc.c

@@ -0,0 +1,56 @@
+// User-level IPC library routines
+
+#include <inc/lib.h>
+
+// Receive a value via IPC and return it.
+// If 'pg' is nonnull, then any page sent by the sender will be mapped at
+//	that address.
+// If 'from_env_store' is nonnull, then store the IPC sender's envid in
+//	*from_env_store.
+// If 'perm_store' is nonnull, then store the IPC sender's page permission
+//	in *perm_store (this is nonzero iff a page was successfully
+//	transferred to 'pg').
+// If the system call fails, then store 0 in *fromenv and *perm (if
+//	they're nonnull) and return the error.
+// Otherwise, return the value sent by the sender
+//
+// Hint:
+//   Use 'thisenv' to discover the value and who sent it.
+//   If 'pg' is null, pass sys_ipc_recv a value that it will understand
+//   as meaning "no page".  (Zero is not the right value, since that's
+//   a perfectly valid place to map a page.)
+int32_t
+ipc_recv(envid_t *from_env_store, void *pg, int *perm_store)
+{
+	// LAB 4: Your code here.
+	panic("ipc_recv not implemented");
+	return 0;
+}
+
+// Send 'val' (and 'pg' with 'perm', if 'pg' is nonnull) to 'toenv'.
+// This function keeps trying until it succeeds.
+// It should panic() on any error other than -E_IPC_NOT_RECV.
+//
+// Hint:
+//   Use sys_yield() to be CPU-friendly.
+//   If 'pg' is null, pass sys_ipc_try_send a value that it will understand
+//   as meaning "no page".  (Zero is not the right value.)
+void
+ipc_send(envid_t to_env, uint32_t val, void *pg, int perm)
+{
+	// LAB 4: Your code here.
+	panic("ipc_send not implemented");
+}
+
+// Find the first environment of the given type.  We'll use this to
+// find special environments.
+// Returns 0 if no such environment exists.
+envid_t
+ipc_find_env(enum EnvType type)
+{
+	int i;
+	for (i = 0; i < NENV; i++)
+		if (envs[i].env_type == type)
+			return envs[i].env_id;
+	return 0;
+}

lib/pfentry.S

@@ -0,0 +1,82 @@
+#include <inc/mmu.h>
+#include <inc/memlayout.h>
+
+// Page fault upcall entrypoint.
+
+// This is where we ask the kernel to redirect us to whenever we cause
+// a page fault in user space (see the call to sys_set_pgfault_handler
+// in pgfault.c).
+//
+// When a page fault actually occurs, the kernel switches our ESP to
+// point to the user exception stack if we're not already on the user
+// exception stack, and then it pushes a UTrapframe onto our user
+// exception stack:
+//
+//	trap-time esp
+//	trap-time eflags
+//	trap-time eip
+//	utf_regs.reg_eax
+//	...
+//	utf_regs.reg_esi
+//	utf_regs.reg_edi
+//	utf_err (error code)
+//	utf_fault_va            <-- %esp
+//
+// If this is a recursive fault, the kernel will reserve for us a
+// blank word above the trap-time esp for scratch work when we unwind
+// the recursive call.
+//
+// We then have call up to the appropriate page fault handler in C
+// code, pointed to by the global variable '_pgfault_handler'.
+
+.text
+.globl _pgfault_upcall
+_pgfault_upcall:
+	// Call the C page fault handler.
+	pushl %esp			// function argument: pointer to UTF
+	movl _pgfault_handler, %eax
+	call *%eax
+	addl $4, %esp			// pop function argument
+	
+	// Now the C page fault handler has returned and you must return
+	// to the trap time state.
+	// Push trap-time %eip onto the trap-time stack.
+	//
+	// Explanation:
+	//   We must prepare the trap-time stack for our eventual return to
+	//   re-execute the instruction that faulted.
+	//   Unfortunately, we can't return directly from the exception stack:
+	//   We can't call 'jmp', since that requires that we load the address
+	//   into a register, and all registers must have their trap-time
+	//   values after the return.
+	//   We can't call 'ret' from the exception stack either, since if we
+	//   did, %esp would have the wrong value.
+	//   So instead, we push the trap-time %eip onto the *trap-time* stack!
+	//   Below we'll switch to that stack and call 'ret', which will
+	//   restore %eip to its pre-fault value.
+	//
+	//   In the case of a recursive fault on the exception stack,
+	//   note that the word we're pushing now will fit in the
+	//   blank word that the kernel reserved for us.
+	//
+	// Throughout the remaining code, think carefully about what
+	// registers are available for intermediate calculations.  You
+	// may find that you have to rearrange your code in non-obvious
+	// ways as registers become unavailable as scratch space.
+	//
+	// LAB 4: Your code here.
+
+	// Restore the trap-time registers.  After you do this, you
+	// can no longer modify any general-purpose registers.
+	// LAB 4: Your code here.
+
+	// Restore eflags from the stack.  After you do this, you can
+	// no longer use arithmetic operations or anything else that
+	// modifies eflags.
+	// LAB 4: Your code here.
+
+	// Switch back to the adjusted trap-time stack.
+	// LAB 4: Your code here.
+
+	// Return to re-execute the instruction that faulted.
+	// LAB 4: Your code here.

lib/pgfault.c

@@ -0,0 +1,37 @@
+// User-level page fault handler support.
+// Rather than register the C page fault handler directly with the
+// kernel as the page fault handler, we register the assembly language
+// wrapper in pfentry.S, which in turns calls the registered C
+// function.
+
+#include <inc/lib.h>
+
+
+// Assembly language pgfault entrypoint defined in lib/pfentry.S.
+extern void _pgfault_upcall(void);
+
+// Pointer to currently installed C-language pgfault handler.
+void (*_pgfault_handler)(struct UTrapframe *utf);
+
+//
+// Set the page fault handler function.
+// If there isn't one yet, _pgfault_handler will be 0.
+// The first time we register a handler, we need to
+// allocate an exception stack (one page of memory with its top
+// at UXSTACKTOP), and tell the kernel to call the assembly-language
+// _pgfault_upcall routine when a page fault occurs.
+//
+void
+set_pgfault_handler(void (*handler)(struct UTrapframe *utf))
+{
+	int r;
+
+	if (_pgfault_handler == 0) {
+		// First time through!
+		// LAB 4: Your code here.
+		panic("set_pgfault_handler not implemented");
+	}
+
+	// Save handler pointer for assembly to call.
+	_pgfault_handler = handler;
+}

lib/printfmt.c

@@ -26,6 +26,8 @@ static const char * const error_string[MAXERROR] =
 	[E_NO_MEM]	= "out of memory",
 	[E_NO_FREE_ENV]	= "out of environments",
 	[E_FAULT]	= "segmentation fault",
+	[E_IPC_NOT_RECV]= "env is not recving",
+	[E_EOF]		= "unexpected end of file",
 };
 
 /*

lib/syscall.c

@@ -61,3 +61,53 @@ sys_getenvid(void)
 	 return syscall(SYS_getenvid, 0, 0, 0, 0, 0, 0);
 }
 
+void
+sys_yield(void)
+{
+	syscall(SYS_yield, 0, 0, 0, 0, 0, 0);
+}
+
+int
+sys_page_alloc(envid_t envid, void *va, int perm)
+{
+	return syscall(SYS_page_alloc, 1, envid, (uint32_t) va, perm, 0, 0);
+}
+
+int
+sys_page_map(envid_t srcenv, void *srcva, envid_t dstenv, void *dstva, int perm)
+{
+	return syscall(SYS_page_map, 1, srcenv, (uint32_t) srcva, dstenv, (uint32_t) dstva, perm);
+}
+
+int
+sys_page_unmap(envid_t envid, void *va)
+{
+	return syscall(SYS_page_unmap, 1, envid, (uint32_t) va, 0, 0, 0);
+}
+
+// sys_exofork is inlined in lib.h
+
+int
+sys_env_set_status(envid_t envid, int status)
+{
+	return syscall(SYS_env_set_status, 1, envid, status, 0, 0, 0);
+}
+
+int
+sys_env_set_pgfault_upcall(envid_t envid, void *upcall)
+{
+	return syscall(SYS_env_set_pgfault_upcall, 1, envid, (uint32_t) upcall, 0, 0, 0);
+}
+
+int
+sys_ipc_try_send(envid_t envid, uint32_t value, void *srcva, int perm)
+{
+	return syscall(SYS_ipc_try_send, 0, envid, value, (uint32_t) srcva, perm, 0);
+}
+
+int
+sys_ipc_recv(void *dstva)
+{
+	return syscall(SYS_ipc_recv, 1, (uint32_t)dstva, 0, 0, 0, 0);
+}
+