Don't assume 4 kB pages.

[pintos-anon] / src / filesys / filehdr.c

diff --git a/src/filesys/filehdr.c b/src/filesys/filehdr.c
index 2f24d3bb1134c9925bb594643a675a88d8618a7e..58179128ae27782bfbc5c4b1fdf5af244484ec4f 100644 (file)
--- a/src/filesys/filehdr.c
+++ b/src/filesys/filehdr.c
@@ -1,10 +1,18 @@
-#include "filehdr.h"
-#include "bitmap.h"
-#include "debug.h"
-#include "malloc.h"
-#include "filesys.h"
-#include "lib.h"
-
+#include "filesys/filehdr.h"
+#include <bitmap.h>
+#include <debug.h>
+#include <stdio.h>
+#include "filesys/filesys.h"
+#include "threads/malloc.h"
+
+/* Allocates sectors from bitmap B for the content of a file
+   whose size is LENGTH bytes, and returns a new `struct filehdr'
+   properly initialized for the file.
+   It is the caller's responsible to allocate a sector for the
+   file header itself, and to write the file header and bitmap
+   to disk.
+   If memory or disk allocation fails, returns a null pointer,
+   leaving bitmap B is unchanged. */
 struct filehdr *
 filehdr_allocate (struct bitmap *b, off_t length) 
 {
@@ -14,18 +22,22 @@ filehdr_allocate (struct bitmap *b, off_t length)
   ASSERT (b != NULL);
   ASSERT (length >= 0);
 
+  sector_cnt = (length / DISK_SECTOR_SIZE) + (length % DISK_SECTOR_SIZE > 0);
+  if (sector_cnt > DIRECT_CNT)
+    return false;
+
   h = calloc (1, sizeof *h);
   if (h == NULL)
     return NULL;
 
   h->length = length;
-  sector_cnt = (length / DISK_SECTOR_SIZE) + (length % DISK_SECTOR_SIZE > 0);
   while (h->sector_cnt < sector_cnt)
     {
       size_t sector = bitmap_find_and_set (b);
       if (sector == BITMAP_ERROR)
         {
           filehdr_deallocate (h, b);
+          free (h);
           return NULL;
         }
       h->sectors[h->sector_cnt++] = sector;
@@ -34,6 +46,8 @@ filehdr_allocate (struct bitmap *b, off_t length)
   return h;
 }
 
+/* Marks the sectors for H's content as free in bitmap B.
+   Neither H's own disk sector nor its memory are freed. */
 void
 filehdr_deallocate (struct filehdr *h, struct bitmap *b) 
 {
@@ -46,6 +60,9 @@ filehdr_deallocate (struct filehdr *h, struct bitmap *b)
     bitmap_reset (b, h->sectors[i]);
 }
 
+/* Reads a file header from FILEHDR_SECTOR
+   and returns a new `struct filehdr' that contains it.
+   Returns a null pointer fi memory allocation fails. */
 struct filehdr *
 filehdr_read (disk_sector_t filehdr_sector) 
 {
@@ -59,6 +76,7 @@ filehdr_read (disk_sector_t filehdr_sector)
   return h;
 }
 
+/* Writes H to disk in sector FILEHDR_SECTOR. */
 void
 filehdr_write (const struct filehdr *h, disk_sector_t filehdr_sector) 
 {
@@ -67,12 +85,18 @@ filehdr_write (const struct filehdr *h, disk_sector_t filehdr_sector)
   disk_write (filesys_disk, filehdr_sector, h);
 }
 
+/* Frees the memory (but not the on-disk sector) associated with
+   H. */
 void
 filehdr_destroy (struct filehdr *h) 
 {
   free (h);
 }
 
+/* Returns the disk sector that contains byte offset POS within
+   the file with header H.
+   Returns -1 if H does not contain data for a byte at offset
+   POS. */
 disk_sector_t
 filehdr_byte_to_sector (const struct filehdr *h, off_t pos) 
 {
@@ -84,6 +108,7 @@ filehdr_byte_to_sector (const struct filehdr *h, off_t pos)
   return idx < h->sector_cnt ? h->sectors[idx] : (disk_sector_t) -1;
 }
 
+/* Returns the length, in bytes, of the file with header H, */
 off_t
 filehdr_length (const struct filehdr *h)
 {
@@ -91,4 +116,22 @@ filehdr_length (const struct filehdr *h)
   return h->length;
 }
 
-void filehdr_print (const struct filehdr *);
+/* Prints a representation of H to the system console. */
+void
+filehdr_print (const struct filehdr *h) 
+{
+  size_t i;
+  
+  printf ("File header: %jd bytes, %zd sectors (",
+          (intmax_t) h->length, h->sector_cnt);
+
+  /* This loop could be unsafe for large h->sector_cnt, can you
+     see why? */
+  for (i = 0; i < h->sector_cnt; i++) 
+    {
+      if (i != 0)
+        printf (", ");
+      printf ("%jd", (intmax_t) h->sectors[i]); 
+    }
+  printf (")\n");
+}