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Author: jserv

inode.c

@@ -11,7 +11,15 @@
 static const struct inode_operations simplefs_inode_ops;
 static const struct inode_operations symlink_inode_ops;
 
-/* Get inode ino from disk */
+/* Either return the inode that corresponds to a given inode number (ino), if
+ * it is already in the cache, or create a new inode object if it is not in the
+ * cache.
+ *
+ * Note that this function is very similar to simplefs_new_inode, except that
+ * the requested inode is supposed to be allocated on-disk already. So do not
+ * use this to create a completely new inode that has not been allocated on
+ * disk.
+ */
 struct inode *simplefs_iget(struct super_block *sb, unsigned long ino)
 {
     struct inode *inode = NULL;
@@ -181,7 +189,17 @@ static struct dentry *simplefs_lookup(struct inode *dir,
     return NULL;
 }
 
-/* Create a new inode in dir */
+/* Find and construct a new inode.
+ *
+ * @dir: the inode of the parent directory where the new inode is supposed to
+ *       be attached to.
+ * @mode: the mode information of the new inode
+ *
+ * This is a helper function for the inode operation "create" (implemented in
+ * simplefs_create()). It takes care of reserving an inode block on disk (by
+ * modifying the inode bitmap), creating a VFS inode object (in memory), and
+ * attaching filesystem-specific information to that VFS inode.
+ */
 static struct inode *simplefs_new_inode(struct inode *dir, mode_t mode)
 {
     struct inode *inode;

simplefs.h

@@ -80,6 +80,9 @@ struct simplefs_sb_info {
 #define SIMPLEFS_AT_LEAST(major, minor, rev) \
     LINUX_VERSION_CODE >= KERNEL_VERSION(major, minor, rev)
 
+/* A 'container' structure that keeps the VFS inode and additional on-disk
+ * data.
+ */
 struct simplefs_inode_info {
     uint32_t ei_block; /* Block with list of extents for this file */
     char i_data[32];
@@ -132,6 +135,7 @@ extern uint32_t simplefs_ext_search(struct simplefs_file_ei_block *index,
 
 /* Getters for superblock and inode */
 #define SIMPLEFS_SB(sb) (sb->s_fs_info)
+/* Extract a simplefs_inode_info object from a VFS inode */
 #define SIMPLEFS_INODE(inode) \
     (container_of(inode, struct simplefs_inode_info, vfs_inode))
 #endif /* __KERNEL__ */

super.c

@@ -16,6 +16,9 @@ struct dentry *simplefs_mount(struct file_system_type *fs_type,
 void simplefs_kill_sb(struct super_block *sb);
 static struct kmem_cache *simplefs_inode_cache;
 
+/* Needed to initiate the inode cache, to allow us to attach
+ * filesystem-specific inode information.
+ */
 int simplefs_init_inode_cache(void)
 {
     simplefs_inode_cache = kmem_cache_create_usercopy(
@@ -26,6 +29,7 @@ int simplefs_init_inode_cache(void)
     return 0;
 }
 
+/* De-allocate the inode cache */
 void simplefs_destroy_inode_cache(void)
 {
     kmem_cache_destroy(simplefs_inode_cache);