Add helper functions to initialise the memory-mapped files table and counter

src/threads/thread.c

@@ -16,6 +16,7 @@
 #include "threads/synch.h"
 #include "threads/vaddr.h"
 #include "vm/page.h"
+#include "vm/mmap.h"
 #ifdef USERPROG
 #include "userprog/process.h"
 #include "userprog/syscall.h"
@@ -274,6 +275,8 @@ thread_create (const char *name, int priority,
     }
 #endif
 
+  mmap_init ();
+
   /* Prepare thread for first run by initializing its stack.
      Do this atomically so intermediate values for the 'stack' 
      member cannot be observed. */

src/vm/mmap.c

@@ -1 +1,35 @@
 #include "mmap.h"
+#include "threads/malloc.h"
+
+static unsigned mmap_hash (const struct hash_elem *e, void *aux);
+static bool mmap_less (const struct hash_elem *a_, const struct hash_elem *b_,
+                void *aux);
+
+/* Initializes the mmap table for the current thread. Sets the counter to 0. */
+bool
+mmap_init (void)
+{
+  struct thread *t = thread_current ();
+  t->mmap_counter = 0;
+  return hash_init (&t->mmap_files, mmap_hash, mmap_less, NULL);
+}
+
+/* A hash function for the mmap table. Returns a hash for an entry, based on its
+   mapping. */
+static unsigned
+mmap_hash (const struct hash_elem *e, void *aux UNUSED)
+{
+  return hash_entry (e, struct mmap_entry, elem)->mapping;
+}
+
+/* A comparator function for the mmap table. Compares two entries based on their
+   mappings. */
+static bool
+mmap_less (const struct hash_elem *a_, const struct hash_elem *b_,
+                void *aux UNUSED)
+{
+  const struct mmap_entry *a = hash_entry (a_, struct mmap_entry, elem);
+  const struct mmap_entry *b = hash_entry (b_, struct mmap_entry, elem);
+
+  return a->mapping < b->mapping;
+}

src/vm/mmap.h

@@ -2,6 +2,7 @@
 #define VM_MMAP_H
 
 #include <hash.h>
+#include "threads/thread.h"
 
 /* A mapping identifier type. */
 typedef unsigned mapid_t;
@@ -15,4 +16,6 @@ struct mmap_entry {
   struct hash_elem elem; /* An elem for the hash table. */
 };
 
+bool mmap_init (void);
+
 #endif /* vm/mmap.h */