Implement the unmap system call, writing back to the file if a page is dirty before removing from SPT

src/userprog/syscall.c

@@ -459,11 +459,42 @@ syscall_mmap (int fd, void *addr)
 
 /* Handles the syscall for unmapping a memory mapped file.
 
-    Pre: mapping is a valid mapping identifier returned by mmap syscall.*/
+    Pre: mapping is a valid mapping identifier returned by mmap syscall. */
 static void
 syscall_munmap (mapid_t mapping)
 {
+  /* Get the mmap entry from the mapping identifier. */
+  struct mmap_entry *mmap = mmap_get (mapping);
 
+  /* Free all the pages associated with the mapping, writing back to the file
+     if necessary. */
+  off_t length = file_length (mmap->file);
+  for (off_t ofs = 0; ofs < length; ofs += PGSIZE)
+    {
+      void *upage = mmap->upage + ofs;
+
+      /* Get the SPT page entry for this page. */
+      struct page_entry *page = page_get(upage);
+      if (page == NULL)
+        continue;
+
+      /* Write the page back to the file if it is dirty. */
+      if (pagedir_is_dirty (thread_current ()->pagedir, upage))
+        {
+          lock_acquire (&filesys_lock);
+          file_write_at (mmap->file, upage, page->read_bytes, ofs);
+          lock_release (&filesys_lock);
+        }
+
+      /* Remove the page from the supplemental page table. */
+      hash_delete (&thread_current ()->pages, &page->elem);
+    }
+
+  /* Remove the mapping from the mmap table. Close the file and free the mmap
+     entry. */
+  hash_delete (&thread_current ()->mmap_files, &mmap->elem);
+  file_close (mmap->file);
+  free(mmap);
 }
 
 /* Hashing function needed for the open_file table. Returns a hash for an entry,

src/vm/mmap.c

@@ -1,5 +1,9 @@
 #include "mmap.h"
+#include "page.h"
+#include "threads/vaddr.h"
 #include "threads/malloc.h"
+#include "userprog/syscall.h"
+#include "userprog/pagedir.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_,
@@ -50,6 +54,44 @@ mmap_insert (struct file *file, void *upage)
   return mmap;
 }
 
+/* Unmaps the given mmap entry from the current thread's mmap table. */
+void
+mmap_unmap (struct mmap_entry *mmap)
+{
+  if (mmap == NULL)
+    return;
+
+  /* Free all the pages associated with the mapping, writing back to the file
+     if necessary. */
+  off_t length = file_length (mmap->file);
+  for (off_t ofs = 0; ofs < length; ofs += PGSIZE)
+  {
+    void *upage = mmap->upage + ofs;
+
+    /* Get the SPT page entry for this page. */
+    struct page_entry *page = page_get(upage);
+    if (page == NULL)
+      continue;
+
+    /* Write the page back to the file if it is dirty. */
+    if (pagedir_is_dirty (thread_current ()->pagedir, upage))
+    {
+      lock_acquire (&filesys_lock);
+      file_write_at (mmap->file, upage, page->read_bytes, ofs);
+      lock_release (&filesys_lock);
+    }
+
+    /* Remove the page from the supplemental page table. */
+    hash_delete (&thread_current ()->pages, &page->elem);
+  }
+
+  /* Remove the mapping from the mmap table. Close the file and free the mmap
+     entry. */
+  hash_delete (&thread_current ()->mmap_files, &mmap->elem);
+  file_close (mmap->file);
+  free(mmap);
+}
+
 /* Destroys the mmap table for the current thread. Frees all the memory
    allocated for the mmap entries. */
 void

src/vm/mmap.h

@@ -20,6 +20,7 @@ struct mmap_entry {
 bool mmap_init (struct thread *t);
 struct mmap_entry *mmap_get (mapid_t mapping);
 struct mmap_entry *mmap_insert (struct file *file, void *upage);
+void mmap_unmap (struct mmap_entry *mmap);
 void mmap_destroy (void);
 
 #endif /* vm/mmap.h */