+/*
+ * A directory consists of some number of blocks of DIRBLKSIZ
+ * bytes, where DIRBLKSIZ is chosen such that it can be transferred
+ * to disk in a single atomic operation (e.g. 512 bytes on most machines).
+ *
+ * Each DIRBLKSIZ byte block contains some number of directory entry
+ * structures, which are of variable length. Each directory entry has
+ * a struct direct at the front of it, containing its inode number,
+ * the length of the entry, and the length of the name contained in
+ * the entry. These are followed by the name padded to a 4 byte boundary
+ * with null bytes. All names are guaranteed null terminated.
+ * The maximum length of a name in a directory is MAXNAMLEN.
+ *
+ * The macro DIRSIZ(dp) gives the amount of space required to represent
+ * a directory entry. Free space in a directory is represented by
+ * entries which have dp->d_reclen > DIRSIZ(dp). All DIRBLKSIZ bytes
+ * in a directory block are claimed by the directory entries. This
+ * usually results in the last entry in a directory having a large
+ * dp->d_reclen. When entries are deleted from a directory, the
+ * space is returned to the previous entry in the same directory
+ * block by increasing its dp->d_reclen. If the first entry of
+ * a directory block is free, then its dp->d_ino is set to 0.
+ * Entries other than the first in a directory do not normally have
+ * dp->d_ino set to 0.
+ */
+#ifdef KERNEL
+#define DIRBLKSIZ DEV_BSIZE
+#else
+#define DIRBLKSIZ 512