Changeset 89ee7ff in mainline for uspace/srv/fs/fat/fat_fat.c

Timestamp:

2010-01-30T18:52:22Z (14 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

ab4bace

Parents:

c713aa56 (diff), 7efc517 (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.

Message:

Merge VFS and FAT fixes.

File:

• uspace/srv/fs/fat/fat_fat.c (modified) (1 diff)

uspace/srv/fs/fat/fat_fat.c

@@ -608 +608 @@
 }
 
+/** Perform basic sanity checks on the file system.
+ *
+ * Verify if values of boot sector fields are sane. Also verify media
+ * descriptor. This is used to rule out cases when a device obviously
+ * does not contain a fat file system.
+ */
+int fat_sanity_check(fat_bs_t *bs, dev_handle_t dev_handle)
+{
+        fat_cluster_t e0, e1;
+        unsigned fat_no;
+        int rc;
+
+        /* Check number of FATs. */
+        if (bs->fatcnt == 0)
+                return ENOTSUP;
+
+        /* Check total number of sectors. */
+
+        if (bs->totsec16 == 0 && bs->totsec32 == 0)
+                return ENOTSUP;
+
+        if (bs->totsec16 != 0 && bs->totsec32 != 0 &&
+            bs->totsec16 != bs->totsec32) 
+                return ENOTSUP;
+
+        /* Check media descriptor. Must be between 0xf0 and 0xff. */
+        if ((bs->mdesc & 0xf0) != 0xf0)
+                return ENOTSUP;
+
+        /* Check number of sectors per FAT. */
+        if (bs->sec_per_fat == 0)
+                return ENOTSUP;
+
+        /*
+         * Check that the root directory entries take up whole blocks.
+         * This check is rather strict, but it allows us to treat the root
+         * directory and non-root directories uniformly in some places.
+         * It can be removed provided that functions such as fat_read() are
+         * sanitized to support file systems with this property.
+         */
+        if ((uint16_t_le2host(bs->root_ent_max) * sizeof(fat_dentry_t)) %
+            uint16_t_le2host(bs->bps) != 0)
+                return ENOTSUP;
+
+        /* Check signature of each FAT. */
+
+        for (fat_no = 0; fat_no < bs->fatcnt; fat_no++) {
+                rc = fat_get_cluster(bs, dev_handle, fat_no, 0, &e0);
+                if (rc != EOK)
+                        return EIO;
+
+                rc = fat_get_cluster(bs, dev_handle, fat_no, 1, &e1);
+                if (rc != EOK)
+                        return EIO;
+
+                /* Check that first byte of FAT contains the media descriptor. */
+                if ((e0 & 0xff) != bs->mdesc)
+                        return ENOTSUP;
+
+                /*
+                 * Check that remaining bits of the first two entries are
+                 * set to one.
+                 */
+                if ((e0 >> 8) != 0xff || e1 != 0xffff)
+                        return ENOTSUP;
+        }
+
+        return EOK;
+}
+
 /**
  * @}