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Annotation of 42BSD/sys/h/dir.h, revision 1.1.1.1

1.1       root        1: /*     dir.h   6.1     83/07/29        */
                      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: /* so user programs can just include dir.h */
                     29: #if !defined(KERNEL) && !defined(DEV_BSIZE)
                     30: #define        DEV_BSIZE       512
                     31: #endif
                     32: #define DIRBLKSIZ      DEV_BSIZE
                     33: #define        MAXNAMLEN       255
                     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
                     72: 
                     73: #ifdef KERNEL
                     74: /*
                     75:  * Template for manipulating directories.
                     76:  * Should use struct direct's, but the name field
                     77:  * is MAXNAMLEN - 1, and this just won't do.
                     78:  */
                     79: struct dirtemplate {
                     80:        u_long  dot_ino;
                     81:        short   dot_reclen;
                     82:        short   dot_namlen;
                     83:        char    dot_name[4];            /* must be multiple of 4 */
                     84:        u_long  dotdot_ino;
                     85:        short   dotdot_reclen;
                     86:        short   dotdot_namlen;
                     87:        char    dotdot_name[4];         /* ditto */
                     88: };
                     89: #endif

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