/*
 * 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
#endif

#define MAXNAMLEN 255

/*
 * The DIRSIZ macro gives the minimum record length which will hold
 * the directory entry. This requires the amount of space in struct direct
 * without the d_name field, plus enough space for the name with a terminating
 * null byte (dp->d_namlen+1), rounded up to a 4 byte boundary.
 */
#undef DIRSIZ
#define DIRSIZ(dp) \e
 ((sizeof (struct direct) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3))

struct direct {
 u_long d_ino;
 short d_reclen;
 short d_namlen;
 char d_name[MAXNAMLEN + 1];
 /* typically shorter */
};

struct _dirdesc {
 int dd_fd;
 long dd_loc;
 long dd_size;
 char dd_buf[DIRBLKSIZ];
};