paxdir.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

/*
	opendir -- open a directory stream
  
	last edit:	16-Jun-1987	D A Gwyn
*/

#include	<sys/errno.h>
#include	<sys/types.h>
#include	<sys/stat.h>
#include	"paxdir.h"

#ifdef BSD_SYSV
/*
	<sys/_dir.h> -- definitions for 4.2,4.3BSD directories
  
	last edit:	25-Apr-1987	D A Gwyn
  
	A directory consists of some number of blocks of DIRBLKSIZ bytes each,
	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 the
	beginning of a (struct direct) at the front of it, containing its
	filesystem-unique ident number, the length of the entry, and the length
	of the name contained in the entry.  These are followed by the NUL-
	terminated name padded to a (long) boundary with 0 bytes.  The maximum
	length of a name in a directory is MAXNAMELEN.
  
	The macro DIRSIZ(dp) gives the amount of space required to represent a
	directory entry.  Free space in a directory is represented by entries
	that 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_fileno is set to 0; entries other than the first in a
	directory do not normally have 	dp->d_fileno set to 0.
  
	prerequisite:	<sys/types.h>
*/

#if defined(accel) || defined(sun) || defined(vax)
#define	DIRBLKSIZ	512	/* size of directory block */
#else
#ifdef alliant
#define	DIRBLKSIZ	4096	/* size of directory block */
#else
#ifdef gould
#define	DIRBLKSIZ	1024	/* size of directory block */
#else
#ifdef ns32000			/* Dynix System V */
#define	DIRBLKSIZ	2600	/* size of directory block */
#else				/* be conservative; multiple blocks are okay
				 * but fractions are not */
#define	DIRBLKSIZ	4096	/* size of directory block */
#endif
#endif
#endif
#endif

#define	MAXNAMELEN	255	/* maximum filename length */
/* NOTE:  not MAXNAMLEN, which has been preempted by SVR3 <dirent.h> */

struct direct {			/* data from read()/_getdirentries() */
    unsigned long   d_fileno;	/* unique ident of entry */
    unsigned short  d_reclen;	/* length of this record */
    unsigned short  d_namlen;	/* length of string in d_name */
    char            d_name[MAXNAMELEN + 1];	/* NUL-terminated filename */
};

/*
	The DIRSIZ macro gives the minimum record length which will hold the
	directory entry.  This requires the amount of space in a (struct
	direct) without the d_name field, plus enough space for the name with a
	terminating NUL character, rounded up to a (long) boundary.
  
	(Note that Berkeley didn't properly compensate for struct padding,
	but we nevertheless have to use the same size as the actual system.)
*/

#define	DIRSIZ( dp )	((sizeof(struct direct) - (MAXNAMELEN+1) \
			+ sizeof(long) + (dp)->d_namlen) \
			/ sizeof(long) * sizeof(long))

#else
#include	<sys/dir.h>
#ifdef SYSV3
#undef	MAXNAMLEN		/* avoid conflict with SVR3 */
#endif
 /* Good thing we don't need to use the DIRSIZ() macro! */
#ifdef d_ino			/* 4.3BSD/NFS using d_fileno */
#undef	d_ino			/* (not absolutely necessary) */
#else
#define	d_fileno	d_ino	/* (struct direct) member */
#endif
#endif
#ifdef UNK
#ifndef UFS
#include "***** ERROR ***** UNK applies only to UFS"
/* One could do something similar for getdirentries(), but I didn't bother. */
#endif
#include	<signal.h>
#endif

#if defined(UFS) + defined(BFS) + defined(NFS) != 1	/* sanity check */
#include "***** ERROR ***** exactly one of UFS, BFS, or NFS must be defined"
#endif

#ifdef UFS
#define	RecLen( dp )	(sizeof(struct direct))	/* fixed-length entries */
#else				/* BFS || NFS */
#define	RecLen( dp )	((dp)->d_reclen)	/* variable-length entries */
#endif

#ifdef NFS
#ifdef BSD_SYSV
#define	getdirentries	_getdirentries	/* package hides this system call */
#endif
extern int      getdirentries();
static long     dummy;		/* getdirentries() needs basep */
#define	GetBlock( fd, buf, n )	getdirentries( fd, buf, (unsigned)n, &dummy )
#else				/* UFS || BFS */
#ifdef BSD_SYSV
#define read	_read		/* avoid emulation overhead */
#endif
extern int      read();
#define	GetBlock( fd, buf, n )	read( fd, buf, (unsigned)n )
#endif

#ifdef UNK
extern int      _getdents();	/* actual system call */
#endif

extern char    *strncpy();
extern int      fstat();
extern OFFSET   lseek();

extern int      errno;

#ifndef DIRBLKSIZ
#define	DIRBLKSIZ	4096	/* directory file read buffer size */
#endif

#ifndef NULL
#define	NULL	0
#endif

#ifndef SEEK_CUR
#define	SEEK_CUR	1
#endif

#ifndef S_ISDIR			/* macro to test for directory file */
#define	S_ISDIR( mode )		(((mode) & S_IFMT) == S_IFDIR)
#endif


#ifndef SEEK_CUR
#define	SEEK_CUR	1
#endif

#ifdef BSD_SYSV
#define open	_open		/* avoid emulation overhead */
#endif

extern int      getdents();	/* SVR3 system call, or emulation */

typedef char   *pointer;	/* (void *) if you have it */

extern void     free();
extern pointer  malloc();
extern int
open(), close(), fstat();

extern int      errno;
extern OFFSET   lseek();

#ifndef SEEK_SET
#define	SEEK_SET	0
#endif

typedef int     bool;		/* Boolean data type */
#define	false	0
#define	true	1


#ifndef NULL
#define	NULL	0
#endif

#ifndef O_RDONLY
#define	O_RDONLY	0
#endif

#ifndef S_ISDIR			/* macro to test for directory file */
#define	S_ISDIR( mode )		(((mode) & S_IFMT) == S_IFDIR)
#endif

#ifdef __STDC__

DIR *opendir(char *dirname)

#else
    
DIR *opendir(dirname)
char           *dirname;	/* name of directory */

#endif
{
    register DIR   *dirp;	/* -> malloc'ed storage */
    register int    fd;		/* file descriptor for read */
    struct stat     sbuf;	/* result of fstat() */

    if ((fd = open(dirname, O_RDONLY)) < 0)
	return ((DIR *)NULL);		/* errno set by open() */

    if (fstat(fd, &sbuf) != 0 || !S_ISDIR(sbuf.st_mode)) {
	close(fd);
	errno = ENOTDIR;
	return ((DIR *)NULL);		/* not a directory */
    }
    if ((dirp = (DIR *) malloc(sizeof(DIR))) == (DIR *)NULL
	|| (dirp->dd_buf = (char *) malloc((unsigned) DIRBUF)) == (char *)NULL
	) {
	register int    serrno = errno;
	/* errno set to ENOMEM by sbrk() */

	if (dirp != (DIR *)NULL)
	    free((pointer) dirp);

	close(fd);
	errno = serrno;
	return ((DIR *)NULL);		/* not enough memory */
    }
    dirp->dd_fd = fd;
    dirp->dd_loc = dirp->dd_size = 0;	/* refill needed */

    return dirp;
}


/*
 *	closedir -- close a directory stream
 *
 *	last edit:	11-Nov-1988	D A Gwyn
 */

#ifdef __STDC__

int closedir(register DIR *dirp)

#else
    
int closedir(dirp)
register DIR	*dirp;		/* stream from opendir() */

#endif
{
    register int	fd;

    if ( dirp == (DIR *)NULL || dirp->dd_buf == (char *)NULL ) {
	errno = EFAULT;
	return -1;			/* invalid pointer */
    }

    fd = dirp->dd_fd;			/* bug fix thanks to R. Salz */
    free( (pointer)dirp->dd_buf );
    free( (pointer)dirp );
    return close( fd );
}


/*
	readdir -- read next entry from a directory stream
  
	last edit:	25-Apr-1987	D A Gwyn
*/

#ifdef __STDC__

struct dirent  *readdir(register DIR *dirp)

#else
    
struct dirent  *readdir(dirp)
register DIR   *dirp;		/* stream from opendir() */

#endif
{
    register struct dirent *dp;	/* -> directory data */

    if (dirp == (DIR *)NULL || dirp->dd_buf == (char *)NULL) {
	errno = EFAULT;
	return (struct dirent *)NULL;		/* invalid pointer */
    }
    do {
	if (dirp->dd_loc >= dirp->dd_size)	/* empty or obsolete */
	    dirp->dd_loc = dirp->dd_size = 0;

	if (dirp->dd_size == 0	/* need to refill buffer */
	    && (dirp->dd_size =
		getdents(dirp->dd_fd, dirp->dd_buf, (unsigned) DIRBUF)
		) <= 0
	    )
	    return ((struct dirent *)NULL);	/* EOF or error */

	dp = (struct dirent *) & dirp->dd_buf[dirp->dd_loc];
	dirp->dd_loc += dp->d_reclen;
    }
    while (dp->d_ino == 0L);	/* don't rely on getdents() */

    return dp;
}


/*
	seekdir -- reposition a directory stream
  
	last edit:	24-May-1987	D A Gwyn
  
	An unsuccessful seekdir() will in general alter the current
	directory position; beware.
  
	NOTE:	4.nBSD directory compaction makes seekdir() & telldir()
		practically impossible to do right.  Avoid using them!
*/

#ifdef __STDC__

void seekdir(register DIR *dirp, register OFFSET loc)

#else
    
void seekdir(dirp, loc)
register DIR   *dirp;		/* stream from opendir() */
register OFFSET  loc;		/* position from telldir() */

#endif
{
    register bool   rewind;	/* "start over when stymied" flag */

    if (dirp == (DIR *)NULL || dirp->dd_buf == (char *)NULL) {
	errno = EFAULT;
	return;			/* invalid pointer */
    }
    /*