[pintos-anon] / solutions / p2.patch

diff -urp -X pat src/threads/thread.c~ src/threads/thread.c
--- src/threads/thread.c~       2005-03-30 10:26:13.000000000 -0800
+++ src/threads/thread.c        2005-03-30 16:19:26.000000000 -0800
@@ -13,6 +13,7 @@
 #include "threads/synch.h"
 #ifdef USERPROG
 #include "userprog/process.h"
+#include "userprog/syscall.h"
 #endif
 
 /* Random value for struct thread's `magic' member.
@@ -243,16 +244,19 @@ thread_tid (void) 
 void
 thread_exit (void) 
 {
+  struct thread *t = thread_current ();
+
   ASSERT (!intr_context ());
 
 #ifdef USERPROG
   process_exit ();
 #endif
-
+  syscall_exit ();
+  
   /* Just set our status to dying and schedule another process.
      We will be destroyed during the call to schedule_tail(). */
   intr_disable ();
-  thread_current ()->status = THREAD_DYING;
+  t->status = THREAD_DYING;
   schedule ();
   NOT_REACHED ();
 }
@@ -353,6 +357,11 @@ init_thread (struct thread *t, const cha
   strlcpy (t->name, name, sizeof t->name);
   t->stack = (uint8_t *) t + PGSIZE;
   t->priority = priority;
+  list_init (&t->children);
+  t->exit_code = -1;
+  t->wait_status = NULL;
+  list_init (&t->fds);
+  t->next_handle = 2;
   t->magic = THREAD_MAGIC;
 }
 
diff -urp -X pat src/threads/thread.h~ src/threads/thread.h
--- src/threads/thread.h~       2005-03-30 10:26:13.000000000 -0800
+++ src/threads/thread.h        2005-03-30 16:17:45.000000000 -0800
@@ -4,6 +4,7 @@
 #include <debug.h>
 #include <list.h>
 #include <stdint.h>
+#include "threads/synch.h"
 
 /* States in a thread's life cycle. */
 enum thread_status
@@ -89,6 +90,11 @@ struct thread
     uint8_t *stack;                     /* Saved stack pointer. */
     int priority;                       /* Priority. */
 
+    /* Owned by process.c. */
+    int exit_code;                      /* Exit code. */
+    struct wait_status *wait_status;    /* This process's completion status. */
+    struct list children;               /* Completion status of children. */
+
     /* Shared between thread.c and synch.c. */
     struct list_elem elem;              /* List element. */
 
@@ -97,10 +103,29 @@ struct thread
     uint32_t *pagedir;                  /* Page directory. */
 #endif
 
+    /* Owned by syscall.c. */
+    struct list fds;                    /* List of file descriptors. */
+    int next_handle;                    /* Next handle value. */
+
     /* Owned by thread.c. */
     unsigned magic;                     /* Detects stack overflow. */
   };
 
+/* Tracks the completion of a process.
+   Reference held by both the parent, in its `children' list,
+   and by the child, in its `wait_status' pointer. */
+struct wait_status
+  {
+    struct list_elem elem;              /* `children' list element. */
+    struct lock lock;                   /* Protects ref_cnt. */
+    int ref_cnt;                        /* 2=child and parent both alive,
+                                           1=either child or parent alive,
+                                           0=child and parent both dead. */
+    tid_t tid;                          /* Child thread id. */
+    int exit_code;                      /* Child exit code, if dead. */
+    struct semaphore dead;              /* 1=child alive, 0=child dead. */
+  };
+
 void thread_init (void);
 void thread_start (void);
 void thread_tick (void);
diff -urp -X pat src/userprog/exception.c~ src/userprog/exception.c
--- src/userprog/exception.c~   2005-01-01 18:09:59.000000000 -0800
+++ src/userprog/exception.c    2005-03-30 13:26:14.000000000 -0800
@@ -150,6 +150,14 @@ page_fault (struct intr_frame *f) 
   write = (f->error_code & PF_W) != 0;
   user = (f->error_code & PF_U) != 0;
 
+  /* Handle bad dereferences from system call implementations. */
+  if (!user) 
+    {
+      f->eip = (void (*) (void)) f->eax;
+      f->eax = 0;
+      return;
+    }
+
   /* To implement virtual memory, delete the rest of the function
      body, and replace it with code that brings in the page to
      which fault_addr refers. */
diff -urp -X pat src/userprog/process.c~ src/userprog/process.c
--- src/userprog/process.c~     2005-03-30 10:40:10.000000000 -0800
+++ src/userprog/process.c      2005-03-30 16:19:32.000000000 -0800
@@ -14,11 +14,23 @@
 #include "threads/init.h"
 #include "threads/interrupt.h"
 #include "threads/mmu.h"
+#include "threads/malloc.h"
 #include "threads/palloc.h"
 #include "threads/thread.h"
 
 static thread_func execute_thread NO_RETURN;
-static bool load (const char *cmdline, void (**eip) (void), void **esp);
+static bool load (const char *cmd_line, void (**eip) (void), void **esp);
+
+/* Data structure shared between process_execute() in the
+   invoking thread and execute_thread() in the newly invoked
+   thread. */
+struct exec_info 
+  {
+    const char *filename;               /* Program to load. */
+    struct semaphore load_done;         /* "Up"ed when loading complete. */
+    struct wait_status *wait_status;    /* Child process. */
+    bool success;                       /* Program successfully loaded? */
+  };
 
 /* Starts a new thread running a user program loaded from
    FILENAME.  The new thread may be scheduled before
@@ -26,29 +38,33 @@ static bool load (const char *cmdline, v
 tid_t
 process_execute (const char *filename) 
 {
-  char *fn_copy;
+  struct exec_info exec;
   tid_t tid;
 
-  /* Make a copy of FILENAME.
-     Otherwise there's a race between the caller and load(). */
-  fn_copy = palloc_get_page (0);
-  if (fn_copy == NULL)
-    return TID_ERROR;
-  strlcpy (fn_copy, filename, PGSIZE);
+  /* Initialize exec_info. */
+  exec.filename = filename;
+  sema_init (&exec.load_done, 0, "load done");
 
   /* Create a new thread to execute FILENAME. */
-  tid = thread_create (filename, PRI_DEFAULT, execute_thread, fn_copy);
-  if (tid == TID_ERROR)
-    palloc_free_page (fn_copy); 
+  tid = thread_create (filename, PRI_DEFAULT, execute_thread, &exec);
+  if (tid != TID_ERROR)
+    {
+      sema_down (&exec.load_done);
+      if (exec.success)
+        list_push_back (&thread_current ()->children, &exec.wait_status->elem);
+      else
+        tid = TID_ERROR;
+    }
+
   return tid;
 }
 
 /* A thread function that loads a user process and starts it
    running. */
 static void
-execute_thread (void *filename_)
+execute_thread (void *exec_)
 {
-  char *filename = filename_;
+  struct exec_info *exec = exec_;
   struct intr_frame if_;
   bool success;
 
@@ -57,10 +73,28 @@ execute_thread (void *filename_)
   if_.gs = if_.fs = if_.es = if_.ds = if_.ss = SEL_UDSEG;
   if_.cs = SEL_UCSEG;
   if_.eflags = FLAG_IF | FLAG_MBS;
-  success = load (filename, &if_.eip, &if_.esp);
+  success = load (exec->filename, &if_.eip, &if_.esp);
+
+  /* Allocate wait_status. */
+  if (success)
+    {
+      exec->wait_status = thread_current ()->wait_status
+        = malloc (sizeof *exec->wait_status);
+      success = exec->wait_status != NULL; 
+    }
 
-  /* If load failed, quit. */
-  palloc_free_page (filename);
+  /* Initialize wait_status. */
+  if (success) 
+    {
+      lock_init (&exec->wait_status->lock, "child process");
+      exec->wait_status->ref_cnt = 2;
+      exec->wait_status->tid = thread_current ()->tid;
+      sema_init (&exec->wait_status->dead, 0, "dead child");
+    }
+  
+  /* Notify parent thread and clean up. */
+  exec->success = success;
+  sema_up (&exec->load_done);
   if (!success) 
     thread_exit ();
 
@@ -74,19 +108,48 @@ execute_thread (void *filename_)
   NOT_REACHED ();
 }
 
+/* Releases one reference to CS and, if it is now unreferenced,
+   frees it. */
+static void
+release_child (struct wait_status *cs) 
+{
+  int new_ref_cnt;
+  
+  lock_acquire (&cs->lock);
+  new_ref_cnt = --cs->ref_cnt;
+  lock_release (&cs->lock);
+
+  if (new_ref_cnt == 0)
+    free (cs);
+}
+
 /* Waits for thread TID to die and returns its exit status.  If
    it was terminated by the kernel (i.e. killed due to an
    exception), returns -1.  If TID is invalid or if it was not a
    child of the calling process, or if process_wait() has already
    been successfully called for the given TID, returns -1
-   immediately, without waiting.
-
-   This function will be implemented in problem 2-2.  For now, it
-   does nothing. */
+   immediately, without waiting. */
 int
-process_wait (tid_t child_tid UNUSED) 
+process_wait (tid_t child_tid) 
 {
+  struct thread *cur = thread_current ();
+  struct list_elem *e;
+
+  for (e = list_begin (&cur->children); e != list_end (&cur->children);
+       e = list_next (e)) 
+    {
+      struct wait_status *cs = list_entry (e, struct wait_status, elem);
+      if (cs->tid == child_tid) 
+        {
+          int exit_code;
+          list_remove (e);
+          sema_down (&cs->dead);
+          exit_code = cs->exit_code;
+          release_child (cs);
+          return exit_code;
+        }
+    }
   return -1;
 }
 
 /* Free the current process's resources. */
@@ -93,8 +157,29 @@ void
 process_exit (void)
 {
   struct thread *cur = thread_current ();
+  struct list_elem *e, *next;
   uint32_t *pd;
 
+  printf ("%s: exit(%d)\n", cur->name, cur->exit_code);
+
+  /* Notify parent that we're dead. */
+  if (cur->wait_status != NULL) 
+    {
+      struct wait_status *cs = cur->wait_status;
+      cs->exit_code = cur->exit_code;
+      sema_up (&cs->dead);
+      release_child (cs);
+    }
+
+  /* Free entries of children list. */
+  for (e = list_begin (&cur->children); e != list_end (&cur->children);
+       e = next) 
+    {
+      struct wait_status *cs = list_entry (e, struct wait_status, elem);
+      next = list_remove (e);
+      release_child (cs);
+    }
+  
   /* Destroy the current process's page directory and switch back
      to the kernel-only page directory. */
   pd = cur->pagedir;
@@ -192,7 +277,7 @@ struct Elf32_Phdr
 #define PF_R 4          /* Readable. */
 
 static bool load_segment (struct file *, const struct Elf32_Phdr *);
-static bool setup_stack (void **esp);
+static bool setup_stack (const char *cmd_line, void **esp);
 
 /* Aborts loading an executable, with an error message. */
 #define LOAD_ERROR(MSG)                                 \
@@ -208,13 +293,15 @@ static bool setup_stack (void **esp);
    and its initial stack pointer into *ESP.
    Returns true if successful, false otherwise. */
 bool
-load (const char *filename, void (**eip) (void), void **esp) 
+load (const char *cmd_line, void (**eip) (void), void **esp) 
 {
   struct thread *t = thread_current ();
+  char filename[NAME_MAX + 2];
   struct Elf32_Ehdr ehdr;
   struct file *file = NULL;
   off_t file_ofs;
   bool success = false;
+  char *cp;
   int i;
 
   /* Allocate and activate page directory. */
@@ -223,6 +310,14 @@ load (const char *filename, void (**eip)
     LOAD_ERROR (("page directory allocation failed"));
   process_activate ();
 
+  /* Extract filename from command line. */
+  while (*cmd_line == ' ')
+    cmd_line++;
+  strlcpy (filename, cmd_line, sizeof filename);
+  cp = strchr (filename, ' ');
+  if (cp != NULL)
+    *cp = '\0';
+
   /* Open executable file. */
   file = filesys_open (filename);
   if (file == NULL)
@@ -283,7 +378,7 @@ load (const char *filename, void (**eip)
     }
 
   /* Set up stack. */
-  if (!setup_stack (esp))
+  if (!setup_stack (cmd_line, esp))
     goto done;
 
   /* Start address. */
@@ -392,10 +487,92 @@ load_segment (struct file *file, const s
   return true;
 }
 
-/* Create a minimal stack by mapping a zeroed page at the top of
-   user virtual memory. */
+/* Reverse the order of the ARGC pointers to char in ARGV. */
+static void
+reverse (int argc, char **argv) 
+{
+  for (; argc > 1; argc -= 2, argv++) 
+    {
+      char *tmp = argv[0];
+      argv[0] = argv[argc - 1];
+      argv[argc - 1] = tmp;
+    }
+}
+
+/* Pushes the SIZE bytes in BUF onto the stack in KPAGE, whose
+   page-relative stack pointer is *OFS, and then adjusts *OFS
+   appropriately.  The bytes pushed are rounded to a 32-bit
+   boundary.
+
+   If successful, returns a pointer to the newly pushed object.
+   On failure, returns a null pointer. */
+static void *
+push (uint8_t *kpage, size_t *ofs, const void *buf, size_t size) 
+{
+  size_t padsize = ROUND_UP (size, sizeof (uint32_t));
+  if (*ofs < padsize)
+    return NULL;
+
+  *ofs -= padsize;
+  memcpy (kpage + *ofs + (padsize - size), buf, size);
+  return kpage + *ofs + (padsize - size);
+}
+
+/* Sets up command line arguments in KPAGE, which will be mapped
+   to UPAGE in user space.  The command line arguments are taken
+   from CMD_LINE, separated by spaces.  Sets *ESP to the initial
+   stack pointer for the process. */
+static bool
+init_cmd_line (uint8_t *kpage, uint8_t *upage, const char *cmd_line,
+               void **esp) 
+{
+  size_t ofs = PGSIZE;
+  char *const null = NULL;
+  char *cmd_line_copy;
+  char *karg, *saveptr;
+  int argc;
+  char **argv;
+
+  /* Push command line string. */
+  cmd_line_copy = push (kpage, &ofs, cmd_line, strlen (cmd_line) + 1);
+  if (cmd_line_copy == NULL)
+    return false;
+
+  if (push (kpage, &ofs, &null, sizeof null) == NULL)
+    return false;
+
+  /* Parse command line into arguments
+     and push them in reverse order. */
+  argc = 0;
+  for (karg = strtok_r (cmd_line_copy, " ", &saveptr); karg != NULL;
+       karg = strtok_r (NULL, " ", &saveptr))
+    {
+      char *uarg = upage + (karg - (char *) kpage);
+      if (push (kpage, &ofs, &uarg, sizeof uarg) == NULL)
+        return false;
+      argc++;
+    }
+
+  /* Reverse the order of the command line arguments. */
+  argv = (char **) (upage + ofs);
+  reverse (argc, (char **) (kpage + ofs));
+
+  /* Push argv, argc, "return address". */
+  if (push (kpage, &ofs, &argv, sizeof argv) == NULL
+      || push (kpage, &ofs, &argc, sizeof argc) == NULL
+      || push (kpage, &ofs, &null, sizeof null) == NULL)
+    return false;
+
+  /* Set initial stack pointer. */
+  *esp = upage + ofs;
+  return true;
+}
+
+/* Create a minimal stack for T by mapping a page at the
+   top of user virtual memory.  Fills in the page using CMD_LINE
+   and sets *ESP to the stack pointer. */
 static bool
-setup_stack (void **esp) 
+setup_stack (const char *cmd_line, void **esp) 
 {
   uint8_t *kpage;
   bool success = false;
@@ -403,9 +580,9 @@ setup_stack (void **esp) 
   kpage = palloc_get_page (PAL_USER | PAL_ZERO);
   if (kpage != NULL) 
     {
-      success = install_page (((uint8_t *) PHYS_BASE) - PGSIZE, kpage);
-      if (success)
-        *esp = PHYS_BASE;
+      uint8_t *upage = ((uint8_t *) PHYS_BASE) - PGSIZE;
+      if (install_page (upage, kpage))
+        success = init_cmd_line (kpage, upage, cmd_line, esp);
       else
         palloc_free_page (kpage);
     }
diff -urp -X pat src/userprog/syscall.c~ src/userprog/syscall.c
--- src/userprog/syscall.c~     2004-09-26 14:15:17.000000000 -0700
+++ src/userprog/syscall.c      2005-03-30 15:11:37.000000000 -0800
@@ -1,20 +1,478 @@
 #include "userprog/syscall.h"
 #include <stdio.h>
+#include <string.h>
 #include <syscall-nr.h>
+#include "userprog/process.h"
+#include "userprog/pagedir.h"
+#include "devices/kbd.h"
+#include "filesys/filesys.h"
+#include "filesys/file.h"
+#include "threads/init.h"
 #include "threads/interrupt.h"
+#include "threads/malloc.h"
+#include "threads/mmu.h"
+#include "threads/palloc.h"
 #include "threads/thread.h"
-
+ 
+ 
+static int sys_halt (void);
+static int sys_exit (int status);
+static int sys_exec (const char *ufile);
+static int sys_wait (tid_t);
+static int sys_create (const char *ufile, unsigned initial_size);
+static int sys_remove (const char *ufile);
+static int sys_open (const char *ufile);
+static int sys_filesize (int handle);
+static int sys_read (int handle, void *udst_, unsigned size);
+static int sys_write (int handle, void *usrc_, unsigned size);
+static int sys_seek (int handle, unsigned position);
+static int sys_tell (int handle);
+static int sys_close (int handle);
+ 
 static void syscall_handler (struct intr_frame *);
-
+static void copy_in (void *, const void *, size_t);
+ 
+static struct lock fs_lock;
+ 
 void
 syscall_init (void) 
 {
   intr_register (0x30, 3, INTR_ON, syscall_handler, "syscall");
+  lock_init (&fs_lock, "fs");
 }
+ 
+/* System call handler. */
+static void
+syscall_handler (struct intr_frame *f) 
+{
+  typedef int syscall_function (int, int, int);
+
+  /* A system call. */
+  struct syscall 
+    {
+      size_t arg_cnt;           /* Number of arguments. */
+      syscall_function *func;   /* Implementation. */
+    };
+
+  /* Table of system calls. */
+  static const struct syscall syscall_table[] =
+    {
+      {0, (syscall_function *) sys_halt},
+      {1, (syscall_function *) sys_exit},
+      {1, (syscall_function *) sys_exec},
+      {1, (syscall_function *) sys_wait},
+      {2, (syscall_function *) sys_create},
+      {1, (syscall_function *) sys_remove},
+      {1, (syscall_function *) sys_open},
+      {1, (syscall_function *) sys_filesize},
+      {3, (syscall_function *) sys_read},
+      {3, (syscall_function *) sys_write},
+      {2, (syscall_function *) sys_seek},
+      {1, (syscall_function *) sys_tell},
+      {1, (syscall_function *) sys_close},
+    };
+
+  const struct syscall *sc;
+  unsigned call_nr;
+  int args[3];
+
+  /* Get the system call. */
+  copy_in (&call_nr, f->esp, sizeof call_nr);
+  if (call_nr >= sizeof syscall_table / sizeof *syscall_table)
+    thread_exit ();
+  sc = syscall_table + call_nr;
 
+  /* Get the system call arguments. */
+  ASSERT (sc->arg_cnt <= sizeof args / sizeof *args);
+  memset (args, 0, sizeof args);
+  copy_in (args, (uint32_t *) f->esp + 1, sizeof *args * sc->arg_cnt);
+
+  /* Execute the system call,
+     and set the return value. */
+  f->eax = sc->func (args[0], args[1], args[2]);
+}
+ 
+/* Returns true if UADDR is a valid, mapped user address,
+   false otherwise. */
+static bool
+verify_user (const void *uaddr) 
+{
+  return pagedir_get_page (thread_current ()->pagedir, uaddr) != NULL;
+}
+ 
+/* Copies a byte from user address USRC to kernel address DST.
+   USRC must be below PHYS_BASE.
+   Returns true if successful, false if a segfault occurred. */
+static inline bool
+get_user (uint8_t *dst, const uint8_t *usrc)
+{
+  int eax;
+  asm ("mov %%eax, offset 1f; mov %%al, %2; mov %0, %%al; 1:"
+       : "=m" (*dst), "=&a" (eax) : "m" (*usrc));
+  return eax != 0;
+}
+ 
+/* Writes BYTE to user address UDST.
+   UDST must be below PHYS_BASE.
+   Returns true if successful, false if a segfault occurred. */
+static inline bool
+put_user (uint8_t *udst, uint8_t byte)
+{
+  int eax;
+  asm ("mov %%eax, offset 1f; mov %0, %b2; 1:"
+       : "=m" (*udst), "=&a" (eax) : "r" (byte));
+  return eax != 0;
+}
+ 
+/* Copies SIZE bytes from user address USRC to kernel address
+   DST.
+   Call thread_exit() if any of the user accesses are invalid. */
 static void
-syscall_handler (struct intr_frame *f UNUSED) 
+copy_in (void *dst_, const void *usrc_, size_t size) 
+{
+  uint8_t *dst = dst_;
+  const uint8_t *usrc = usrc_;
+ 
+  for (; size > 0; size--, dst++, usrc++) 
+    if (usrc >= (uint8_t *) PHYS_BASE || !get_user (dst, usrc)) 
+      thread_exit ();
+}
+ 
+/* Creates a copy of user string US in kernel memory
+   and returns it as a page that must be freed with
+   palloc_free_page().
+   Truncates the string at PGSIZE bytes in size.
+   Call thread_exit() if any of the user accesses are invalid. */
+static char *
+copy_in_string (const char *us) 
+{
+  char *ks;
+  size_t length;
+ 
+  ks = palloc_get_page (0);
+  if (ks == NULL) 
+    thread_exit ();
+ 
+  for (length = 0; length < PGSIZE; length++)
+    {
+      if (us >= (char *) PHYS_BASE || !get_user (ks + length, us++)) 
+        thread_exit (); 
+       
+      if (ks[length] == '\0')
+        return ks;
+    }
+  ks[PGSIZE - 1] = '\0';
+  return ks;
+}
+ 
+/* Halt system call. */
+static int
+sys_halt (void)
+{
+  power_off ();
+}
+ 
+/* Exit system call. */
+static int
+sys_exit (int exit_code) 
+{
+  thread_current ()->exit_code = exit_code;
+  thread_exit ();
+  NOT_REACHED ();
+}
+ 
+/* Exec system call. */
+static int
+sys_exec (const char *ufile) 
+{
+  tid_t tid;
+  char *kfile = copy_in_string (ufile);
+ 
+  lock_acquire (&fs_lock);
+  tid = process_execute (kfile);
+  lock_release (&fs_lock);
+ 
+  palloc_free_page (kfile);
+ 
+  return tid;
+}
+ 
+/* Wait system call. */
+static int
+sys_wait (tid_t child) 
+{
+  return process_wait (child);
+}
+ 
+/* Create system call. */
+static int
+sys_create (const char *ufile, unsigned initial_size) 
+{
+  char *kfile = copy_in_string (ufile);
+  bool ok;
+   
+  lock_acquire (&fs_lock);
+  ok = filesys_create (kfile, initial_size);
+  lock_release (&fs_lock);
+ 
+  palloc_free_page (kfile);
+ 
+  return ok;
+}
+ 
+/* Remove system call. */
+static int
+sys_remove (const char *ufile) 
 {
-  printf ("system call!\n");
+  char *kfile = copy_in_string (ufile);
+  bool ok;
+   
+  lock_acquire (&fs_lock);
+  ok = filesys_remove (kfile);
+  lock_release (&fs_lock);
+ 
+  palloc_free_page (kfile);
+ 
+  return ok;
+}
+ 
+/* A file descriptor, for binding a file handle to a file. */
+struct file_descriptor
+  {
+    struct list_elem elem;      /* List element. */
+    struct file *file;          /* File. */
+    int handle;                 /* File handle. */
+  };
+ 
+/* Open system call. */
+static int
+sys_open (const char *ufile) 
+{
+  char *kfile = copy_in_string (ufile);
+  struct file_descriptor *fd;
+  int handle = -1;
+ 
+  fd = malloc (sizeof *fd);
+  if (fd != NULL)
+    {
+      lock_acquire (&fs_lock);
+      fd->file = filesys_open (kfile);
+      if (fd->file != NULL)
+        {
+          struct thread *cur = thread_current ();
+          handle = fd->handle = cur->next_handle++;
+          list_push_front (&cur->fds, &fd->elem);
+        }
+      else 
+        free (fd);
+      lock_release (&fs_lock);
+    }
+  
+  palloc_free_page (kfile);
+  return handle;
+}
+ 
+/* Returns the file descriptor associated with the given handle.
+   Terminates the process if HANDLE is not associated with an
+   open file. */
+static struct file_descriptor *
+lookup_fd (int handle) 
+{
+  struct thread *cur = thread_current ();
+  struct list_elem *e;
+   
+  for (e = list_begin (&cur->fds); e != list_end (&cur->fds);
+       e = list_next (e))
+    {
+      struct file_descriptor *fd;
+      fd = list_entry (e, struct file_descriptor, elem);
+      if (fd->handle == handle)
+        return fd;
+    }
+ 
   thread_exit ();
 }
+ 
+/* Filesize system call. */
+static int
+sys_filesize (int handle) 
+{
+  struct file_descriptor *fd = lookup_fd (handle);
+  int size;
+ 
+  lock_acquire (&fs_lock);
+  size = file_length (fd->file);
+  lock_release (&fs_lock);
+ 
+  return size;
+}
+ 
+/* Read system call. */
+static int
+sys_read (int handle, void *udst_, unsigned size) 
+{
+  uint8_t *udst = udst_;
+  struct file_descriptor *fd;
+  int bytes_read = 0;
+
+  /* Handle keyboard reads. */
+  if (handle == STDIN_FILENO) 
+    {
+      for (bytes_read = 0; (size_t) bytes_read < size; bytes_read++)
+        if (udst >= (uint8_t *) PHYS_BASE || !put_user (udst++, kbd_getc ()))
+          thread_exit ();
+      return bytes_read;
+    }
+
+  /* Handle all other reads. */
+  fd = lookup_fd (handle);
+  lock_acquire (&fs_lock);
+  while (size > 0) 
+    {
+      /* How much to read into this page? */
+      size_t page_left = PGSIZE - pg_ofs (udst);
+      size_t read_amt = size < page_left ? size : page_left;
+      off_t retval;
+
+      /* Check that touching this page is okay. */
+      if (!verify_user (udst)) 
+        {
+          lock_release (&fs_lock);
+          thread_exit ();
+        }
+
+      /* Read from file into page. */
+      retval = file_read (fd->file, udst, read_amt);
+      if (retval < 0)
+        {
+          if (bytes_read == 0)
+            bytes_read = -1; 
+          break;
+        }
+      bytes_read += retval;
+
+      /* If it was a short read we're done. */
+      if (retval != (off_t) read_amt)
+        break;
+
+      /* Advance. */
+      udst += retval;
+      size -= retval;
+    }
+  lock_release (&fs_lock);
+   
+  return bytes_read;
+}
+ 
+/* Write system call. */
+static int
+sys_write (int handle, void *usrc_, unsigned size) 
+{
+  uint8_t *usrc = usrc_;
+  struct file_descriptor *fd = NULL;
+  int bytes_written = 0;
+
+  /* Lookup up file descriptor. */
+  if (handle != STDOUT_FILENO)
+    fd = lookup_fd (handle);
+
+  lock_acquire (&fs_lock);
+  while (size > 0) 
+    {
+      /* How much bytes to write to this page? */
+      size_t page_left = PGSIZE - pg_ofs (usrc);
+      size_t write_amt = size < page_left ? size : page_left;
+      off_t retval;
+
+      /* Check that we can touch this user page. */
+      if (!verify_user (usrc)) 
+        {
+          lock_release (&fs_lock);
+          thread_exit ();
+        }
+
+      /* Do the write. */
+      if (handle == STDOUT_FILENO)
+        {
+          putbuf (usrc, write_amt);
+          retval = write_amt;
+        }
+      else
+        retval = file_write (fd->file, usrc, write_amt);
+      if (retval < 0) 
+        {
+          if (bytes_written == 0)
+            bytes_written = -1;
+          break;
+        }
+      bytes_written += retval;
+
+      /* If it was a short write we're done. */
+      if (retval != (off_t) write_amt)
+        break;
+
+      /* Advance. */
+      usrc += retval;
+      size -= retval;
+    }
+  lock_release (&fs_lock);
+ 
+  return bytes_written;
+}
+ 
+/* Seek system call. */
+static int
+sys_seek (int handle, unsigned position) 
+{
+  struct file_descriptor *fd = lookup_fd (handle);
+   
+  lock_acquire (&fs_lock);
+  file_seek (fd->file, position);
+  lock_release (&fs_lock);
+ 
+  return 0;
+}
+ 
+/* Tell system call. */
+static int
+sys_tell (int handle) 
+{
+  struct file_descriptor *fd = lookup_fd (handle);
+  unsigned position;
+   
+  lock_acquire (&fs_lock);
+  position = file_tell (fd->file);
+  lock_release (&fs_lock);
+ 
+  return position;
+}
+ 
+/* Close system call. */
+static int
+sys_close (int handle) 
+{
+  struct file_descriptor *fd = lookup_fd (handle);
+  lock_acquire (&fs_lock);
+  file_close (fd->file);
+  lock_release (&fs_lock);
+  list_remove (&fd->elem);
+  free (fd);
+  return 0;
+}
+ 
+/* On thread exit, close all open files. */
+void
+syscall_exit (void) 
+{
+  struct thread *cur = thread_current ();
+  struct list_elem *e, *next;
+   
+  for (e = list_begin (&cur->fds); e != list_end (&cur->fds); e = next)
+    {
+      struct file_descriptor *fd;
+      fd = list_entry (e, struct file_descriptor, elem);
+      next = list_next (e);
+      file_close (fd->file);
+      free (fd);
+    }
+}
diff -urp -X pat src/userprog/syscall.h~ src/userprog/syscall.h
--- src/userprog/syscall.h~     2004-09-05 22:38:45.000000000 -0700
+++ src/userprog/syscall.h      2005-03-30 13:26:14.000000000 -0800
@@ -2,5 +2,6 @@
 #define USERPROG_SYSCALL_H
 
 void syscall_init (void);
+void syscall_exit (void);
 
 #endif /* userprog/syscall.h */