history.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

		histptr = history - 1;
	}
}

# ifdef EASY_HISTORY
/*
 * save command in history
 */
void
histsave(lno, cmd, dowrite)
	int lno;	/* ignored (compatibility with COMPLEX_HISTORY) */
	const char *cmd;
	int dowrite;	/* ignored (compatibility with COMPLEX_HISTORY) */
{
	register char **hp = histptr;
	char *cp;

	if (++hp >= history + histsize) { /* remove oldest command */
		afree((void*)history[0], APERM);
		memmove(history, history + 1,
			sizeof(history[0]) * (histsize - 1));
		hp = &history[histsize - 1];
	}
	*hp = str_save(cmd, APERM);
	/* trash trailing newline but allow imbedded newlines */
	cp = *hp + strlen(*hp);
	if (cp > *hp && cp[-1] == '\n')
		cp[-1] = '\0';
	histptr = hp;
}

/*
 * Append an entry to the last saved command. Used for multiline
 * commands
 */
void
histappend(cmd, nl_separate)
	const char *cmd;
	int	nl_separate;
{
	int	hlen, clen;
	char	*p;

	hlen = strlen(*histptr);
	clen = strlen(cmd);
	if (clen > 0 && cmd[clen-1] == '\n')
		clen--;
	p = *histptr = (char *) aresize(*histptr, hlen + clen + 2, APERM);
	p += hlen;
	if (nl_separate)
		*p++ = '\n';
	memcpy(p, cmd, clen);
	p[clen] = '\0';
}

/*
 * 92-04-25 <sjg@zen>
 * A simple history file implementation.
 * At present we only save the history when we exit.
 * This can cause problems when there are multiple shells are
 * running under the same user-id.  The last shell to exit gets
 * to save its history.
 */
void
hist_init(s)
	Source *s;
{
	char *f;
	FILE *fh;

	if (Flag(FTALKING) == 0)
		return;

	hstarted = 1;

	hist_source = s;

	if ((f = str_val(global("HISTFILE"))) == NULL || *f == '\0') {
# if 1 /* Don't use history file unless the user asks for it */
		hname = NULL;
		return;
# else
		char *home = str_val(global("HOME"));
		int len;

		if (home == NULL)
			home = null;
		f = HISTFILE;
		hname = alloc(len = strlen(home) + strlen(f) + 2, APERM);
		shf_snprintf(hname, len, "%s/%s", home, f);
# endif
	} else
		hname = str_save(f, APERM);

	if ((fh = fopen(hname, "r"))) {
		int pos = 0, nread = 0;
		int contin = 0;		/* continuation of previous command */
		char *end;
		char hline[LINE + 1];

		while (1) {
			if (pos >= nread) {
				pos = 0;
				nread = fread(hline, 1, LINE, fh);
				if (nread <= 0)
					break;
				hline[nread] = '\0';
			}
			end = strchr(hline + pos, 0); /* will always succeed */
			if (contin)
				histappend(hline + pos, 0);
			else {
				hist_source->line++;
				histsave(0, hline + pos, 0);
			}
			pos = end - hline + 1;
			contin = end == &hline[nread];
		}
		fclose(fh);
	}
}

/*
 * save our history.
 * We check that we do not have more than we are allowed.
 * If the history file is read-only we do nothing.
 * Handy for having all shells start with a useful history set.
 */

void
hist_finish()
{
  static int once;
  FILE *fh;
  register int i;
  register char **hp;

  if (once++)
    return;
  /* check how many we have */
  i = histptr - history;
  if (i >= histsize)
    hp = &histptr[-histsize];
  else
    hp = history;
  if (hname && (fh = fopen(hname, "w")))
  {
    for (i = 0; hp + i <= histptr && hp[i]; i++)
      fprintf(fh, "%s%c", hp[i], '\0');
    fclose(fh);
  }
}

# else /* EASY_HISTORY */

/*
 *	Routines added by Peter Collinson BSDI(Europe)/Hillside Systems to
 *	a) permit HISTSIZE to control number of lines of history stored
 *	b) maintain a physical history file
 *
 *	It turns out that there is a lot of ghastly hackery here
 */


/*
 * save command in history
 */
void
histsave(lno, cmd, dowrite)
	int lno;
	const char *cmd;
	int dowrite;
{
	register char **hp;
	char *c, *cp;

	c = str_save(cmd, APERM);
	if ((cp = strchr(c, '\n')) != NULL)
		*cp = '\0';

	if (histfd && dowrite)
		writehistfile(lno, c);

	hp = histptr;

	if (++hp >= history + histsize) { /* remove oldest command */
		afree((void*)*history, APERM);
		for (hp = history; hp < history + histsize - 1; hp++)
			hp[0] = hp[1];
	}
	*hp = c;
	histptr = hp;
}

/*
 *	Write history data to a file nominated by HISTFILE
 *	if HISTFILE is unset then history still happens, but
 *	the data is not written to a file
 *	All copies of ksh looking at the file will maintain the
 *	same history. This is ksh behaviour.
 *
 *	This stuff uses mmap()
 *	if your system ain't got it - then you'll have to undef HISTORYFILE
 */

/*
 *	Open a history file
 *	Format is:
 *	Bytes 1, 2: HMAGIC - just to check that we are dealing with
 *		    the correct object
 *	Then follows a number of stored commands
 *	Each command is
 *	<command byte><command number(4 bytes)><bytes><null>
 */
# define HMAGIC1		0xab
# define HMAGIC2		0xcd
# define COMMAND		0xff

void
hist_init(s)
	Source *s;
{
	unsigned char	*base;
	int	lines;
	int	fd;

	if (Flag(FTALKING) == 0)
		return;

	hstarted = 1;

	hist_source = s;

	hname = str_val(global("HISTFILE"));
	if (hname == NULL)
		return;
	hname = str_save(hname, APERM);

  retry:
	/* we have a file and are interactive */
	if ((fd = open(hname, O_RDWR|O_CREAT|O_APPEND, 0600)) < 0)
		return;

	histfd = savefd(fd, 0);

	(void) flock(histfd, LOCK_EX);

	hsize = lseek(histfd, 0L, SEEK_END);

	if (hsize == 0) {
		/* add magic */
		if (sprinkle(histfd)) {
			hist_finish();
			return;
		}
	}
	else if (hsize > 0) {
		/*
		 * we have some data
		 */
		base = (unsigned char *)mmap(0, hsize, PROT_READ, MAP_FLAGS, histfd, 0);
		/*
		 * check on its validity
		 */
		if ((int)base == -1 || *base != HMAGIC1 || base[1] != HMAGIC2) {
			if ((int)base !=  -1)
				munmap((caddr_t)base, hsize);
			hist_finish();
			unlink(hname);
			goto retry;
		}
		if (hsize > 2) {
			lines = hist_count_lines(base+2, hsize-2);
			if (lines > histsize) {
				/* we need to make the file smaller */
				if (hist_shrink(base, hsize))
					unlink(hname);
				munmap((caddr_t)base, hsize);
				hist_finish();
				goto retry;
			}
		}
		histload(hist_source, base+2, hsize-2);
		munmap((caddr_t)base, hsize);
	}
	(void) flock(histfd, LOCK_UN);
	hsize = lseek(histfd, 0L, SEEK_END);
}

typedef enum state {
	shdr,		/* expecting a header */
	sline,		/* looking for a null byte to end the line */
	sn1,		/* bytes 1 to 4 of a line no */
	sn2, sn3, sn4,
} State;

static int
hist_count_lines(base, bytes)
	register unsigned char *base;
	register int bytes;
{
	State state = shdr;
	register lines = 0;

	while (bytes--) {
		switch (state)
		{
		case shdr:
			if (*base == COMMAND)
				state = sn1;
			break;
		case sn1:
			state = sn2; break;
		case sn2:
			state = sn3; break;
		case sn3:
			state = sn4; break;
		case sn4:
			state = sline; break;
		case sline:
			if (*base == '\0')
				lines++, state = shdr;
		}
		base++;
	}
	return lines;
}

/*
 *	Shrink the history file to histsize lines
 */
static int
hist_shrink(oldbase, oldbytes)
	unsigned char *oldbase;
	int oldbytes;
{
	int fd;
	char	nfile[1024];
	struct	stat statb;
	unsigned char *nbase = oldbase;
	int nbytes = oldbytes;

	nbase = hist_skip_back(nbase, &nbytes, histsize);
	if (nbase == NULL)
		return 1;
	if (nbase == oldbase)
		return 0;

	/*
	 *	create temp file
	 */
	(void) shf_snprintf(nfile, sizeof(nfile), "%s.%d", hname, procpid);
	if ((fd = creat(nfile, 0600)) < 0)
		return 1;

	if (sprinkle(fd)) {
		close(fd);
		unlink(nfile);
		return 1;
	}
	if (write(fd, nbase, nbytes) != nbytes) {
		close(fd);
		unlink(nfile);
		return 1;
	}
	/*
	 *	worry about who owns this file
	 */
	if (fstat(histfd, &statb) >= 0)
		fchown(fd, statb.st_uid, statb.st_gid);
	close(fd);

	/*
	 *	rename
	 */
	if (rename(nfile, hname) < 0)
		return 1;
	return 0;
}


/*
 *	find a pointer to the data `no' back from the end of the file
 *	return the pointer and the number of bytes left
 */
static unsigned char *
hist_skip_back(base, bytes, no)
	unsigned char *base;
	int *bytes;
	int no;
{
	register int lines = 0;
	register unsigned char *ep;

	for (ep = base + *bytes; --ep > base; ) {
		/* this doesn't really work: the 4 byte line number that is
		 * encoded after the COMMAND byte can itself contain the
		 * COMMAND byte....
		 */
		for (; ep > base && *ep != COMMAND; ep--)
			;
		if (ep == base)
			break;
		if (++lines == no) {
			*bytes = *bytes - ((char *)ep - (char *)base);
			return ep;
		}
	}
	return NULL;
}

/*
 *	load the history structure from the stored data
 */
static void
histload(s, base, bytes)
	Source *s;
	register unsigned char *base;
	register int bytes;
{
	State state;
	int	lno;
	unsigned char	*line;

	for (state = shdr; bytes-- > 0; base++) {
		switch (state) {
		case shdr:
			if (*base == COMMAND)
				state = sn1;
			break;
		case sn1:
			lno = (((*base)&0xff)<<24);
			state = sn2;
			break;
		case sn2:
			lno |= (((*base)&0xff)<<16);
			state = sn3;
			break;
		case sn3:
			lno |= (((*base)&0xff)<<8);
			state = sn4;
			break;
		case sn4:
			lno |= (*base)&0xff;
			line = base+1;
			state = sline;
			break;
		case sline:
			if (*base == '\0') {
				/* worry about line numbers */
				if (histptr >= history && lno-1 != s->line) {
					/* a replacement ? */
					histinsert(s, lno, line);
				}
				else {
					s->line = lno;
					histsave(lno, (char *)line, 0);
				}
				state = shdr;
			}
		}
	}
}

/*
 *	Insert a line into the history at a specified number
 */
static void
histinsert(s, lno, line)
	Source *s;
	int lno;
	unsigned char *line;
{
	register char **hp;

	if (lno >= s->line-(histptr-history) && lno <= s->line) {
		hp = &histptr[lno-s->line];
		if (*hp)
			afree((void*)*hp, APERM);
		*hp = str_save((char *)line, APERM);
	}
}

/*
 *	write a command to the end of the history file
 *	This *MAY* seem easy but it's also necessary to check
 *	that the history file has not changed in size.
 *	If it has - then some other shell has written to it
 *	and we should read those commands to update our history
 */
static void
writehistfile(lno, cmd)
	int lno;
	char *cmd;
{
	int	sizenow;
	unsigned char	*base;
	unsigned char	*new;
	int	bytes;
	char	hdr[5];

	(void) flock(histfd, LOCK_EX);
	sizenow = lseek(histfd, 0L, SEEK_END);
	if (sizenow != hsize) {
		/*
		 *	Things have changed
		 */
		if (sizenow > hsize) {
			/* someone has added some lines */
			bytes = sizenow - hsize;
			base = (unsigned char *)mmap(0, sizenow, PROT_READ, MAP_FLAGS, histfd, 0);
			if ((int)base == -1)
				goto bad;
			new = base + hsize;
			if (*new != COMMAND) {
				munmap((caddr_t)base, sizenow);
				goto bad;
			}
			hist_source->line--;
			histload(hist_source, new, bytes);
			hist_source->line++;
			lno = hist_source->line;
			munmap((caddr_t)base, sizenow);
			hsize = sizenow;
		} else {
			/* it has shrunk */
			/* but to what? */
			/* we'll give up for now */
			goto bad;
		}
	}
	/*
	 *	we can write our bit now
	 */
	hdr[0] = COMMAND;
	hdr[1] = (lno>>24)&0xff;
	hdr[2] = (lno>>16)&0xff;
	hdr[3] = (lno>>8)&0xff;
	hdr[4] = lno&0xff;
	(void) write(histfd, hdr, 5);
	(void) write(histfd, cmd, strlen(cmd)+1);
	hsize = lseek(histfd, 0L, SEEK_END);
	(void) flock(histfd, LOCK_UN);
	return;
bad:
	hist_finish();
}

void
hist_finish()
{
	(void) flock(histfd, LOCK_UN);
	(void) close(histfd);
	histfd = 0;
}

/*
 *	add magic to the history file
 */
static int
sprinkle(fd)
	int fd;
{
	static char mag[] = { HMAGIC1, HMAGIC2 };

	return(write(fd, mag, 2) != 2);
}

# endif
#else /* HISTORY */

/* No history to be compiled in: dummy routines to avoid lots more ifdefs */
void
init_histvec()
{
}
void
hist_init(s)
	Source *s;
{
}
void
hist_finish()
{
}
void
histsave(lno, cmd, dowrite)
	int lno;
	const char *cmd;
	int dowrite;
{
	errorf("history not enabled");
}
#endif /* HISTORY */