buffer.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

/* $Source: /u/mark/src/pax/RCS/buffer.c,v $
 *
 * $Revision: 1.2 $
 *
 * buffer.c - Buffer management functions
 *
 * DESCRIPTION
 *
 *	These functions handle buffer manipulations for the archiving
 *	formats.  Functions are provided to get memory for buffers, 
 *	flush buffers, read and write buffers and de-allocate buffers.  
 *	Several housekeeping functions are provided as well to get some 
 *	information about how full buffers are, etc.
 *
 * AUTHOR
 *
 *	Mark H. Colburn, NAPS International ([e-mail])
 *
 * Sponsored by The USENIX Association for public distribution. 
 *
 * Copyright (c) 1989 Mark H. Colburn.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice is duplicated in all such 
 * forms and that any documentation, advertising materials, and other 
 * materials related to such distribution and use acknowledge that the 
 * software was developed * by Mark H. Colburn and sponsored by The 
 * USENIX Association. 
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * $Log:	buffer.c,v $
 * Revision 1.2  89/02/12  10:04:02  mark
 * 1.2 release fixes
 * 
 * Revision 1.1  88/12/23  18:02:01  mark
 * Initial revision
 * 
 */

#ifndef lint
static char *ident = "$Id: buffer.c,v 1.2 89/02/12 10:04:02 mark Exp $";
static char *copyright = "Copyright (c) 1989 Mark H. Colburn.\nAll rights reserved.\n";
#endif /* ! lint */


/* Headers */

#include "pax.h"


/* Function Prototypes */

#ifdef __STDC__

static int ar_write(int, char *, uint);
static void buf_pad(OFFSET);
static int indata(int, OFFSET, char *);
static void outflush(void);
static void buf_use(uint);
static int buf_in_avail(char **, uint *);
static uint buf_out_avail(char **);

#else /* !__STDC__ */

static int ar_write();
static void buf_pad();
static int indata();
static void outflush();
static void buf_use();
static int buf_in_avail();
static uint buf_out_avail();

#endif /* __STDC__ */


/* inentry - install a single archive entry
 *
 * DESCRIPTION
 *
 *	Inentry reads an archive entry from the archive file and writes it
 *	out the the named file.  If we are in PASS mode during archive
 *	processing, the pass() function is called, otherwise we will
 *	extract from the archive file.
 *
 *	Inentry actaully calls indata to process the actual data to the
 *	file.
 *
 * PARAMETERS
 *
 *	char	*name	- name of the file to extract from the archive
 *	Stat	*asb	- stat block of the file to be extracted from the
 *			  archive.
 *
 * RETURNS
 *
 * 	Returns zero if successful, -1 otherwise. 
 */

#ifdef __STDC__

int inentry(char *name, Stat *asb)

#else

int inentry(name, asb)
char           *name;
Stat           *asb;

#endif
{
    Link           *linkp;
    int             ifd;
    int             ofd;
    time_t          tstamp[2];

    if ((ofd = openout(name, asb, linkp = linkfrom(name, asb), 0)) > 0) {
	if (asb->sb_size || linkp == (Link *)NULL || linkp->l_size == 0) {
	    close(indata(ofd, asb->sb_size, name));
	} else if ((ifd = open(linkp->l_path->p_name, O_RDONLY)) < 0) {
	    warn(linkp->l_path->p_name, strerror());
	} else {
	    passdata(linkp->l_path->p_name, ifd, name, ofd);
	    close(ifd);
	    close(ofd);
	}
    } else {
	return(buf_skip((OFFSET) asb->sb_size) >= 0);
    }
    tstamp[0] = (!f_pass && f_access_time) ? asb->sb_atime : time((time_t *) 0);
    tstamp[1] = f_mtime ? asb->sb_mtime : time((time_t *) 0);
    utime(name, tstamp);
    return (0);
}


/* outdata - write archive data
 *
 * DESCRIPTION
 *
 *	Outdata transfers data from the named file to the archive buffer.
 *	It knows about the file padding which is required by tar, but no
 *	by cpio.  Outdata continues after file read errors, padding with 
 *	null characters if neccessary.   Closes the input file descriptor 
 *	when finished.
 *
 * PARAMETERS
 *
 *	int	fd	- file descriptor of file to read data from
 *	char   *name	- name of file
 *	OFFSET	size	- size of the file
 *
 */

#ifdef __STDC__

void outdata(int fd, char *name, OFFSET size)

#else

void outdata(fd, name, size)
int             fd;
char           *name;
OFFSET          size;

#endif
{
    uint            chunk;
    int             got;
    int             oops;
    uint            avail;
    int		    pad;
    char           *buf;

    oops = got = 0;
    if (pad = (size % BLOCKSIZE)) {
	pad = (BLOCKSIZE - pad);
    }
    while (size) {
	avail = buf_out_avail(&buf);
	size -= (chunk = size < avail ? (uint) size : avail);
	if (oops == 0 && (got = read(fd, buf, (unsigned int) chunk)) < 0) {
	    oops = -1;
	    warn(name, strerror());
	    got = 0;
	}
	if (got < chunk) {
	    if (oops == 0) {
		oops = -1;
	    }
	    warn(name, "Early EOF");
	    while (got < chunk) {
		buf[got++] = '\0';
	    }
	}
	buf_use(chunk);
    }
    close(fd);
    if (ar_format == TAR) {
	buf_pad((OFFSET) pad);
    }
}


/* write_eot -  write the end of archive record(s)
 *
 * DESCRIPTION
 *
 *	Write out an End-Of-Tape record.  We actually zero at least one 
 *	record, through the end of the block.  Old tar writes garbage after 
 *	two zeroed records -- and PDtar used to.
 */

#ifdef __STDC__

void write_eot(void)

#else

void write_eot()

#endif
{
    OFFSET           pad;
    char            header[M_STRLEN + H_STRLEN + 1];

    if (ar_format == TAR) {
	/* write out two zero blocks for trailer */
	pad = 2 * BLOCKSIZE;
    } else {
	if (pad = (total + M_STRLEN + H_STRLEN + TRAILZ) % BLOCKSIZE) {
	    pad = BLOCKSIZE - pad;
	}
	strcpy(header, M_ASCII);
	sprintf(header + M_STRLEN, H_PRINT, 0, 0,
		       0, 0, 0, 1, 0, (time_t) 0, TRAILZ, pad);
	outwrite(header, M_STRLEN + H_STRLEN);
	outwrite(TRAILER, TRAILZ);
    }
    buf_pad((OFFSET) pad);
    outflush();
}

 
/* outwrite -  write archive data
 *
 * DESCRIPTION
 *
 *	Writes out data in the archive buffer to the archive file.  The
 *	buffer index and the total byte count are incremented by the number
 *	of data bytes written.
 *
 * PARAMETERS
 *	
 *	char   *idx	- pointer to data to write
 *	uint	len	- length of the data to write
 */

#ifdef __STDC__

void outwrite(char *idx, uint len)

#else

void outwrite(idx, len)
char           *idx;	/* pointer to data to write */
uint            len;	/* length of data to write */

#endif
{
    uint            have;
    uint            want;
    char           *endx;

    endx = idx + len;
    while (want = endx - idx) {
	if (bufend - bufidx < 0) {
	    fatal("Buffer overlow in out_write\n");
	}
	if ((have = bufend - bufidx) == 0) {
	    outflush();
	}
	if (have > want) {
	    have = want;
	}
	memcpy(bufidx, idx, (int) have);
	bufidx += have;
	idx += have;
	total += have;
    }
}


/* passdata - copy data to one file
 *
 * DESCRIPTION
 *
 *	Copies a file from one place to another.  Doesn't believe in input 
 *	file descriptor zero (see description of kludge in openin() comments). 
 *	Closes the provided output file descriptor. 
 *
 * PARAMETERS
 *
 *	char	*from	- input file name (old file)
 *	int	ifd	- input file descriptor
 *	char	*to	- output file name (new file)
 *	int	ofd	- output file descriptor
 */

#ifdef __STDC__

void passdata(char *from, int ifd, char *to, int ofd)

#else

void passdata(from, ifd, to, ofd)
char           *from;
int             ifd;
char           *to;
int             ofd;

#endif
{
    int             got;
    int             sparse;
    char            block[BUFSIZ];

    if (ifd) {
	lseek(ifd, (OFFSET) 0, 0);
	sparse = 0;
	while ((got = read(ifd, block, sizeof(block))) > 0
	       && (sparse = ar_write(ofd, block, (uint) got)) >= 0) {
	    total += got;
	}
	if (got) {
	    warn(got < 0 ? from : to, strerror());
	} else if (sparse > 0
		 && (lseek(ofd, (OFFSET)(-sparse), 1) < 0
		     || write(ofd, block, (uint) sparse) != sparse)) {
	    warn(to, strerror());
	}
    }
    close(ofd);
}


/* buf_allocate - get space for the I/O buffer 
 *
 * DESCRIPTION
 *
 *	buf_allocate allocates an I/O buffer using malloc.  The resulting
 *	buffer is used for all data buffering throughout the program.
 *	Buf_allocate must be called prior to any use of the buffer or any
 *	of the buffering calls.
 *
 * PARAMETERS
 *
 *	int	size	- size of the I/O buffer to request
 *
 * ERRORS
 *
 *	If an invalid size is given for a buffer or if a buffer of the 
 *	required size cannot be allocated, then the function prints out an 
 *	error message and returns a non-zero exit status to the calling 
 *	process, terminating the program.
 *
 */

#ifdef __STDC__

void buf_allocate(OFFSET size)

#else

void buf_allocate(size)
OFFSET            size;

#endif
{
    if (size <= 0) {
	fatal("invalid value for blocksize");
    }
    if ((bufstart = malloc((unsigned) size)) == (char *)NULL) {
	fatal("Cannot allocate I/O buffer");
    }
    bufend = bufidx = bufstart;
    bufend += size;
}


/* buf_skip - skip input archive data
 *
 * DESCRIPTION
 *
 *	Buf_skip skips past archive data.  It is used when the length of
 *	the archive data is known, and we do not wish to process the data.
 *
 * PARAMETERS
 *
 *	OFFSET	len	- number of bytes to skip
 *
 * RETURNS
 *
 * 	Returns zero under normal circumstances, -1 if unreadable data is 
 * 	encountered. 
 */

#ifdef __STDC__

int buf_skip(OFFSET len)

#else

int buf_skip(len)
OFFSET           len;

#endif
{
    uint            chunk;
    int             corrupt = 0;

    while (len) {
	if (bufend - bufidx < 0) {
	    fatal("Buffer overlow in buf_skip\n");
	}
	while ((chunk = bufend - bufidx) == 0) {