diplodocus.org Git - nmh/blob - docs/historical/mh-6.8.5/miscellany/libndir/dir.h

   1 /*      dir.h   4.4     82/07/25        */
   2
   3 /*
   4  * A directory consists of some number of blocks of DIRBLKSIZ
   5  * bytes, where DIRBLKSIZ is chosen such that it can be transferred
   6  * to disk in a single atomic operation (e.g. 512 bytes on most machines).
   7  *
   8  * Each DIRBLKSIZ byte block contains some number of directory entry
   9  * structures, which are of variable length.  Each directory entry has
  10  * a struct direct at the front of it, containing its inode number,
  11  * the length of the entry, and the length of the name contained in
  12  * the entry.  These are followed by the name padded to a 4 byte boundary
  13  * with null bytes.  All names are guaranteed null terminated.
  14  * The maximum length of a name in a directory is MAXNAMLEN.
  15  *
  16  * The macro DIRSIZ(dp) gives the amount of space required to represent
  17  * a directory entry.  Free space in a directory is represented by
  18  * entries which have dp->d_reclen >= DIRSIZ(dp).  All DIRBLKSIZ bytes
  19  * in a directory block are claimed by the directory entries.  This
  20  * usually results in the last entry in a directory having a large
  21  * dp->d_reclen.  When entries are deleted from a directory, the
  22  * space is returned to the previous entry in the same directory
  23  * block by increasing its dp->d_reclen.  If the first entry of
  24  * a directory block is free, then its dp->d_ino is set to 0.
  25  * Entries other than the first in a directory do not normally have
  26  * dp->d_ino set to 0.
  27  */
  28 #define DIRBLKSIZ       512
  29 #define MAXNAMLEN       255
  30
  31 #ifdef pdp11
  32 #define u_long long
  33 #endif
  34
  35 struct  direct {
  36         u_long  d_ino;                  /* inode number of entry */
  37         u_short d_reclen;               /* length of this record */
  38         u_short d_namlen;               /* length of string in d_name */
  39         char    d_name[MAXNAMLEN + 1];  /* name must be no longer than this */
  40 };
  41
  42 /*
  43  * The DIRSIZ macro gives the minimum record length which will hold
  44  * the directory entry.  This requires the amount of space in struct direct
  45  * without the d_name field, plus enough space for the name with a terminating
  46  * null byte (dp->d_namlen+1), rounded up to a 4 byte boundary.
  47  */
  48 #undef DIRSIZ
  49 #define DIRSIZ(dp) \
  50     ((sizeof (struct direct) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3))
  51
  52 #ifndef KERNEL
  53 /*
  54  * Definitions for library routines operating on directories.
  55  */
  56 typedef struct _dirdesc {
  57         int     dd_fd;
  58         long    dd_loc;
  59         long    dd_size;
  60         char    dd_buf[DIRBLKSIZ];
  61 } DIR;
  62 #ifndef NULL
  63 #define NULL 0
  64 #endif
  65 extern  DIR *opendir();
  66 extern  struct direct *readdir();
  67 extern  long telldir();
  68 extern  void seekdir();
  69 #define rewinddir(dirp) seekdir((dirp), (long)0)
  70 extern  void closedir();
  71 #endif KERNEL