libbb/xfuncs.c - codeaurora/busybox - Gitiles

 /* vi: set sw=4 ts=4: */
 /*
  * Utility routines.
  *
  * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
  * Copyright (C) 2006 Rob Landley
  * Copyright (C) 2006 Denis Vlasenko
  *
  * Licensed under GPL version 2, see file LICENSE in this tarball for details.
  */

 #include "busybox.h"

 /* All the functions starting with "x" call bb_error_msg_and_die() if they
  * fail, so callers never need to check for errors.  If it returned, it
  * succeeded. */

 #ifndef DMALLOC
 /* dmalloc provides variants of these that do abort() on failure.
  * Since dmalloc's prototypes overwrite the impls here as they are
  * included after these prototypes in libbb.h, all is well.
  */
 #ifdef L_xmalloc
 // Die if we can't allocate size bytes of memory.
 void *xmalloc(size_t size)
 {
 	void *ptr = malloc(size);
 	if (ptr == NULL && size != 0)
 		bb_error_msg_and_die(bb_msg_memory_exhausted);
 	return ptr;
 }
 #endif

 #ifdef L_xrealloc
 // Die if we can't resize previously allocated memory.  (This returns a pointer
 // to the new memory, which may or may not be the same as the old memory.
 // It'll copy the contents to a new chunk and free the old one if necessary.)
 void *xrealloc(void *ptr, size_t size)
 {
 	ptr = realloc(ptr, size);
 	if (ptr == NULL && size != 0)
 		bb_error_msg_and_die(bb_msg_memory_exhausted);
 	return ptr;
 }
 #endif
 #endif /* DMALLOC */


 #ifdef L_xzalloc
 // Die if we can't allocate and zero size bytes of memory.
 void *xzalloc(size_t size)
 {
 	void *ptr = xmalloc(size);
 	memset(ptr, 0, size);
 	return ptr;
 }
 #endif

 #ifdef L_xstrdup
 // Die if we can't copy a string to freshly allocated memory.
 char * xstrdup(const char *s)
 {
 	char *t;

 	if (s == NULL)
 		return NULL;

 	t = strdup (s);

 	if (t == NULL)
 		bb_error_msg_and_die(bb_msg_memory_exhausted);

 	return t;
 }
 #endif

 #ifdef L_xstrndup
 // Die if we can't allocate n+1 bytes (space for the null terminator) and copy
 // the (possibly truncated to length n) string into it.
 char * xstrndup(const char *s, int n)
 {
 	char *t;

 	if (ENABLE_DEBUG && s == NULL)
 		bb_error_msg_and_die("xstrndup bug");

 	t = xmalloc(++n);

 	return safe_strncpy(t,s,n);
 }
 #endif

 #ifdef L_xfopen
 // Die if we can't open a file and return a FILE * to it.
 // Notice we haven't got xfread(), This is for use with fscanf() and friends.
 FILE *xfopen(const char *path, const char *mode)
 {
 	FILE *fp;
 	if ((fp = fopen(path, mode)) == NULL)
 		bb_perror_msg_and_die("%s", path);
 	return fp;
 }
 #endif

 #ifdef L_xopen
 // Die if we can't open an existing file and return an fd.
 int xopen(const char *pathname, int flags)
 {
 	if (ENABLE_DEBUG && (flags & O_CREAT))
 		bb_error_msg_and_die("xopen() with O_CREAT");

 	return xopen3(pathname, flags, 0777);
 }
 #endif

 #ifdef L_xopen3
 // Die if we can't open a new file and return an fd.
 int xopen3(const char *pathname, int flags, int mode)
 {
 	int ret;

 	ret = open(pathname, flags, mode);
 	if (ret < 0) {
 		bb_perror_msg_and_die("%s", pathname);
 	}
 	return ret;
 }
 #endif

 #ifdef L_xread
 // Die with an error message if we can't read the entire buffer.
 void xread(int fd, void *buf, size_t count)
 {
 	while (count) {
 		ssize_t size;

 		if ((size = safe_read(fd, buf, count)) < 1)
 			bb_error_msg_and_die("Short read");
 		count -= size;
 		buf = ((char *) buf) + size;
 	}
 }
 #endif

 #ifdef L_xwrite
 // Die with an error message if we can't write the entire buffer.
 void xwrite(int fd, void *buf, size_t count)
 {
 	while (count) {
 		ssize_t size;

 		if ((size = safe_write(fd, buf, count)) < 1)
 			bb_error_msg_and_die("Short write");
 		count -= size;
 		buf = ((char *) buf) + size;
 	}
 }
 #endif

 #ifdef L_xlseek
 // Die with an error message if we can't lseek to the right spot.
 void xlseek(int fd, off_t offset, int whence)
 {
 	if (offset != lseek(fd, offset, whence)) bb_error_msg_and_die("lseek");
 }
 #endif

 #ifdef L_xread_char
 // Die with an error message if we can't read one character.
 unsigned char xread_char(int fd)
 {
 	char tmp;

 	xread(fd, &tmp, 1);

 	return(tmp);
 }
 #endif

 #ifdef L_xferror
 // Die with supplied error message if this FILE * has ferror set.
 void xferror(FILE *fp, const char *fn)
 {
 	if (ferror(fp)) {
 		bb_error_msg_and_die("%s", fn);
 	}
 }
 #endif

 #ifdef L_xferror_stdout
 // Die with an error message if stdout has ferror set.
 void xferror_stdout(void)
 {
 	xferror(stdout, bb_msg_standard_output);
 }
 #endif

 #ifdef L_xfflush_stdout
 // Die with an error message if we have trouble flushing stdout.
 void xfflush_stdout(void)
 {
 	if (fflush(stdout)) {
 		bb_perror_msg_and_die(bb_msg_standard_output);
 	}
 }
 #endif

 #ifdef L_spawn
 // This does a fork/exec in one call, using vfork().  Return PID of new child,
 // -1 for failure.  Runs argv[0], searching path if that has no / in it.
 pid_t spawn(char **argv)
 {
 	static int failed;
 	pid_t pid;
 	void *app = ENABLE_FEATURE_SH_STANDALONE_SHELL ? find_applet_by_name(argv[0]) : 0;

 	// Be nice to nommu machines.
 	failed = 0;
 	pid = vfork();
 	if (pid < 0) return pid;
 	if (!pid) {
 		execvp(app ? CONFIG_BUSYBOX_EXEC_PATH : *argv, argv);

 		// We're sharing a stack with blocked parent, let parent know we failed
 		// and then exit to unblock parent (but don't run atexit() stuff, which
 		// would screw up parent.)

 		failed = -1;
 		_exit(0);
 	}
 	return failed ? failed : pid;
 }
 #endif

 #ifdef L_xspawn
 // Die with an error message if we can't spawn a child process.
 pid_t xspawn(char **argv)
 {
 	pid_t pid = spawn(argv);
 	if (pid < 0) bb_perror_msg_and_die("%s", *argv);
 	return pid;
 }
 #endif

 #ifdef L_wait4
 // Wait for the specified child PID to exit, returning child's error return.
 int wait4pid(int pid)
 {
 	int status;

 	if (pid == -1 || waitpid(pid, &status, 0) == -1) return -1;
 	if (WIFEXITED(status)) return WEXITSTATUS(status);
 	if (WIFSIGNALED(status)) return WTERMSIG(status);
 	return 0;
 }
 #endif

 #ifdef L_xsetenv
 void xsetenv(const char *key, const char *value)
 {
 	if(setenv(key, value, 1))
 		bb_error_msg_and_die(bb_msg_memory_exhausted);
 }
 #endif

 #ifdef L_itoa
 // Convert unsigned integer to ascii, writing into supplied buffer.  A
 // truncated result is always null terminated (unless buflen is 0), and
 // contains the first few digits of the result ala strncpy.
 void utoa_to_buf(unsigned n, char *buf, unsigned buflen)
 {
 	int i, out = 0;
 	if (buflen) {
 		for (i=1000000000; i; i/=10) {
 			int res = n/i;

 			if ((res || out || i == 1) && --buflen>0) {
 				out++;
 				n -= res*i;
 				*buf++ = '0' + res;
 			}
 		}
 		*buf = 0;
 	}
 }

 // Convert signed integer to ascii, like utoa_to_buf()
 void itoa_to_buf(int n, char *buf, unsigned buflen)
 {
 	if (buflen && n<0) {
 		n = -n;
 		*buf++ = '-';
 		buflen--;
 	}
 	utoa_to_buf((unsigned)n, buf, buflen);
 }

 // The following two functions use a static buffer, so calling either one a
 // second time will overwrite previous results.
 //
 // The largest 32 bit integer is -2 billion plus null terminator, or 12 bytes.
 // Int should always be 32 bits on any remotely Unix-like system, see
 // http://www.unix.org/whitepapers/64bit.html for the reasons why.

 static char local_buf[12];

 // Convert unsigned integer to ascii using a static buffer (returned).
 char *utoa(unsigned n)
 {
 	utoa_to_buf(n, local_buf, sizeof(local_buf));

 	return local_buf;
 }

 // Convert signed integer to ascii using a static buffer (returned).
 char *itoa(int n)
 {
 	itoa_to_buf(n, local_buf, sizeof(local_buf));

 	return local_buf;
 }
 #endif

 #ifdef L_setuid
 // Die with an error message if we can't set gid.  (Because resource limits may
 // limit this user to a given number of processes, and if that fills up the
 // setgid() will fail and we'll _still_be_root_, which is bad.)
 void xsetgid(gid_t gid)
 {
 	if (setgid(gid)) bb_error_msg_and_die("setgid");
 }

 // Die with an error message if we cant' set uid.  (See xsetgid() for why.)
 void xsetuid(uid_t uid)
 {
 	if (setuid(uid)) bb_error_msg_and_die("setuid");
 }
 #endif

 #ifdef L_fdlength
 // Return how long the file at fd is, if there's any way to determine it.
 off_t fdlength(int fd)
 {
 	off_t bottom = 0, top = 0, pos;
 	long size;

 	// If the ioctl works for this, return it.

 	if (ioctl(fd, BLKGETSIZE, &size) >= 0) return size*512;

 	// If not, do a binary search for the last location we can read.  (Some
 	// block devices don't do BLKGETSIZE right.)

 	do {
 		char temp;

 		pos = bottom + (top - bottom) / 2;

 		// If we can read from the current location, it's bigger.

 		if (lseek(fd, pos, 0)>=0 && safe_read(fd, &temp, 1)==1) {
 			if (bottom == top) bottom = top = (top+1) * 2;
 			else bottom = pos;

 		// If we can't, it's smaller.

 		} else {
 			if (bottom == top) {
 				if (!top) return 0;
 				bottom = top/2;
 			}
 			else top = pos;
 		}
 	} while (bottom + 1 != top);

 	return pos + 1;
 }
 #endif

 #ifdef L_xasprintf
 // Die with an error message if we can't malloc() enough space and do an
 // sprintf() into that space.
 char *xasprintf(const char *format, ...)
 {
 	va_list p;
 	int r;
 	char *string_ptr;

 #if 1
 	// GNU extension
 	va_start(p, format);
 	r = vasprintf(&string_ptr, format, p);
 	va_end(p);
 #else
 	// Bloat for systems that haven't got the GNU extension.
 	va_start(p, format);
 	r = vsnprintf(NULL, 0, format, p);
 	va_end(p);
 	string_ptr = xmalloc(r+1);
 	va_start(p, format);
 	r = vsnprintf(string_ptr, r+1, format, p);
 	va_end(p);
 #endif

 	if (r < 0) bb_error_msg_and_die(bb_msg_memory_exhausted);
 	return string_ptr;
 }
 #endif

 #ifdef L_xprint_and_close_file
 // Die with an error message if we can't copy an entire FILE * to stdout, then
 // close that file.
 void xprint_and_close_file(FILE *file)
 {
 	// copyfd outputs error messages for us.
 	if (bb_copyfd_eof(fileno(file), 1) == -1)
 		exit(xfunc_error_retval);

 	fclose(file);
 }
 #endif

 #ifdef L_xchdir
 // Die if we can't chdir to a new path.
 void xchdir(const char *path)
 {
 	if (chdir(path))
 		bb_perror_msg_and_die("chdir(%s)", path);
 }
 #endif

 #ifdef L_warn_opendir
 // Print a warning message if opendir() fails, but don't die.
 DIR *warn_opendir(const char *path)
 {
 	DIR *dp;

 	if ((dp = opendir(path)) == NULL) {
 		bb_perror_msg("unable to open `%s'", path);
 		return NULL;
 	}
 	return dp;
 }
 #endif

 #ifdef L_xopendir
 // Die with an error message if opendir() fails.
 DIR *xopendir(const char *path)
 {
 	DIR *dp;

 	if ((dp = opendir(path)) == NULL)
 		bb_perror_msg_and_die("unable to open `%s'", path);
 	return dp;
 }
 #endif

 #ifdef L_xdaemon
 #ifndef BB_NOMMU
 // Die with an error message if we can't daemonize.
 void xdaemon(int nochdir, int noclose)
 {
 	if (daemon(nochdir, noclose)) bb_perror_msg_and_die("daemon");
 }
 #endif
 #endif

 #ifdef L_xsocket
 // Die with an error message if we can't open a new socket.
 int xsocket(int domain, int type, int protocol)
 {
 	int r = socket(domain, type, protocol);

 	if (r < 0) bb_perror_msg_and_die("socket");

 	return r;
 }
 #endif

 #ifdef L_xbind
 // Die with an error message if we can't bind a socket to an address.
 void xbind(int sockfd, struct sockaddr *my_addr, socklen_t addrlen)
 {
 	if (bind(sockfd, my_addr, addrlen)) bb_perror_msg_and_die("bind");
 }
 #endif

 #ifdef L_xlisten
 // Die with an error message if we can't listen for connections on a socket.
 void xlisten(int s, int backlog)
 {
 	if (listen(s, backlog)) bb_perror_msg_and_die("listen");
 }
 #endif

 #ifdef L_xstat
 // xstat() - a stat() which dies on failure with meaningful error message
 void xstat(char *name, struct stat *stat_buf)
 {
 	if (stat(name, stat_buf))
 		bb_perror_msg_and_die("can't stat '%s'", name);
 }
 #endif

 #ifdef L_get_terminal_width_height
 /* It is perfectly ok to pass in a NULL for either width or for
  *  * height, in which case that value will not be set.  */
 int get_terminal_width_height(int fd, int *width, int *height)
 {
 	struct winsize win = { 0, 0, 0, 0 };
 	int ret = ioctl(fd, TIOCGWINSZ, &win);
 	if (!win.ws_row) {
 		char *s = getenv("LINES");
 		if (s) win.ws_row = atoi(s);
 	}
 	if (win.ws_row <= 1) win.ws_row = 24;
 	if (!win.ws_col) {
 		char *s = getenv("COLUMNS");
 		if (s) win.ws_col = atoi(s);
 	}
 	if (win.ws_col <= 1) win.ws_col = 80;
 	if (height) *height = (int) win.ws_row;
 	if (width) *width = (int) win.ws_col;

 	return ret;
 }
 #endif
	/* vi: set sw=4 ts=4: */
	/*
	* Utility routines.
	*
	* Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
	* Copyright (C) 2006 Rob Landley
	* Copyright (C) 2006 Denis Vlasenko
	*
	* Licensed under GPL version 2, see file LICENSE in this tarball for details.
	*/

	#include "busybox.h"

	/* All the functions starting with "x" call bb_error_msg_and_die() if they
	* fail, so callers never need to check for errors. If it returned, it
	* succeeded. */

	#ifndef DMALLOC
	/* dmalloc provides variants of these that do abort() on failure.
	* Since dmalloc's prototypes overwrite the impls here as they are
	* included after these prototypes in libbb.h, all is well.
	*/
	#ifdef L_xmalloc
	// Die if we can't allocate size bytes of memory.
	void *xmalloc(size_t size)
	{
	void *ptr = malloc(size);
	if (ptr == NULL && size != 0)
	bb_error_msg_and_die(bb_msg_memory_exhausted);
	return ptr;
	}
	#endif

	#ifdef L_xrealloc
	// Die if we can't resize previously allocated memory. (This returns a pointer
	// to the new memory, which may or may not be the same as the old memory.
	// It'll copy the contents to a new chunk and free the old one if necessary.)
	void xrealloc(void ptr, size_t size)
	{
	ptr = realloc(ptr, size);
	if (ptr == NULL && size != 0)
	bb_error_msg_and_die(bb_msg_memory_exhausted);
	return ptr;
	}
	#endif
	#endif /* DMALLOC */


	#ifdef L_xzalloc
	// Die if we can't allocate and zero size bytes of memory.
	void *xzalloc(size_t size)
	{
	void *ptr = xmalloc(size);
	memset(ptr, 0, size);
	return ptr;
	}
	#endif

	#ifdef L_xstrdup
	// Die if we can't copy a string to freshly allocated memory.
	char * xstrdup(const char *s)
	{
	char *t;

	if (s == NULL)
	return NULL;

	t = strdup (s);

	if (t == NULL)
	bb_error_msg_and_die(bb_msg_memory_exhausted);

	return t;
	}
	#endif

	#ifdef L_xstrndup
	// Die if we can't allocate n+1 bytes (space for the null terminator) and copy
	// the (possibly truncated to length n) string into it.
	char * xstrndup(const char *s, int n)
	{
	char *t;

	if (ENABLE_DEBUG && s == NULL)
	bb_error_msg_and_die("xstrndup bug");

	t = xmalloc(++n);

	return safe_strncpy(t,s,n);
	}
	#endif

	#ifdef L_xfopen
	// Die if we can't open a file and return a FILE * to it.
	// Notice we haven't got xfread(), This is for use with fscanf() and friends.
	FILE xfopen(const char path, const char *mode)
	{
	FILE *fp;
	if ((fp = fopen(path, mode)) == NULL)
	bb_perror_msg_and_die("%s", path);
	return fp;
	}
	#endif

	#ifdef L_xopen
	// Die if we can't open an existing file and return an fd.
	int xopen(const char *pathname, int flags)
	{
	if (ENABLE_DEBUG && (flags & O_CREAT))
	bb_error_msg_and_die("xopen() with O_CREAT");

	return xopen3(pathname, flags, 0777);
	}
	#endif

	#ifdef L_xopen3
	// Die if we can't open a new file and return an fd.
	int xopen3(const char *pathname, int flags, int mode)
	{
	int ret;

	ret = open(pathname, flags, mode);
	if (ret < 0) {
	bb_perror_msg_and_die("%s", pathname);
	}
	return ret;
	}
	#endif

	#ifdef L_xread
	// Die with an error message if we can't read the entire buffer.
	void xread(int fd, void *buf, size_t count)
	{
	while (count) {
	ssize_t size;

	if ((size = safe_read(fd, buf, count)) < 1)
	bb_error_msg_and_die("Short read");
	count -= size;
	buf = ((char *) buf) + size;
	}
	}
	#endif

	#ifdef L_xwrite
	// Die with an error message if we can't write the entire buffer.
	void xwrite(int fd, void *buf, size_t count)
	{
	while (count) {
	ssize_t size;

	if ((size = safe_write(fd, buf, count)) < 1)
	bb_error_msg_and_die("Short write");
	count -= size;
	buf = ((char *) buf) + size;
	}
	}
	#endif

	#ifdef L_xlseek
	// Die with an error message if we can't lseek to the right spot.
	void xlseek(int fd, off_t offset, int whence)
	{
	if (offset != lseek(fd, offset, whence)) bb_error_msg_and_die("lseek");
	}
	#endif

	#ifdef L_xread_char
	// Die with an error message if we can't read one character.
	unsigned char xread_char(int fd)
	{
	char tmp;

	xread(fd, &tmp, 1);

	return(tmp);
	}
	#endif

	#ifdef L_xferror
	// Die with supplied error message if this FILE * has ferror set.
	void xferror(FILE fp, const char fn)
	{
	if (ferror(fp)) {
	bb_error_msg_and_die("%s", fn);
	}
	}
	#endif

	#ifdef L_xferror_stdout
	// Die with an error message if stdout has ferror set.
	void xferror_stdout(void)
	{
	xferror(stdout, bb_msg_standard_output);
	}
	#endif

	#ifdef L_xfflush_stdout
	// Die with an error message if we have trouble flushing stdout.
	void xfflush_stdout(void)
	{
	if (fflush(stdout)) {
	bb_perror_msg_and_die(bb_msg_standard_output);
	}
	}
	#endif

	#ifdef L_spawn
	// This does a fork/exec in one call, using vfork(). Return PID of new child,
	// -1 for failure. Runs argv[0], searching path if that has no / in it.
	pid_t spawn(char **argv)
	{
	static int failed;
	pid_t pid;
	void *app = ENABLE_FEATURE_SH_STANDALONE_SHELL ? find_applet_by_name(argv[0]) : 0;

	// Be nice to nommu machines.
	failed = 0;
	pid = vfork();
	if (pid < 0) return pid;
	if (!pid) {
	execvp(app ? CONFIG_BUSYBOX_EXEC_PATH : *argv, argv);

	// We're sharing a stack with blocked parent, let parent know we failed
	// and then exit to unblock parent (but don't run atexit() stuff, which
	// would screw up parent.)

	failed = -1;
	_exit(0);
	}
	return failed ? failed : pid;
	}
	#endif

	#ifdef L_xspawn
	// Die with an error message if we can't spawn a child process.
	pid_t xspawn(char **argv)
	{
	pid_t pid = spawn(argv);
	if (pid < 0) bb_perror_msg_and_die("%s", *argv);
	return pid;
	}
	#endif

	#ifdef L_wait4
	// Wait for the specified child PID to exit, returning child's error return.
	int wait4pid(int pid)
	{
	int status;

	if (pid == -1 \|\| waitpid(pid, &status, 0) == -1) return -1;
	if (WIFEXITED(status)) return WEXITSTATUS(status);
	if (WIFSIGNALED(status)) return WTERMSIG(status);
	return 0;
	}
	#endif

	#ifdef L_xsetenv
	void xsetenv(const char key, const char value)
	{
	if(setenv(key, value, 1))
	bb_error_msg_and_die(bb_msg_memory_exhausted);
	}
	#endif

	#ifdef L_itoa
	// Convert unsigned integer to ascii, writing into supplied buffer. A
	// truncated result is always null terminated (unless buflen is 0), and
	// contains the first few digits of the result ala strncpy.
	void utoa_to_buf(unsigned n, char *buf, unsigned buflen)
	{
	int i, out = 0;
	if (buflen) {
	for (i=1000000000; i; i/=10) {
	int res = n/i;

	if ((res \|\| out \|\| i == 1) && --buflen>0) {
	out++;
	n -= res*i;
	*buf++ = '0' + res;
	}
	}
	*buf = 0;
	}
	}

	// Convert signed integer to ascii, like utoa_to_buf()
	void itoa_to_buf(int n, char *buf, unsigned buflen)
	{
	if (buflen && n<0) {
	n = -n;
	*buf++ = '-';
	buflen--;
	}
	utoa_to_buf((unsigned)n, buf, buflen);
	}

	// The following two functions use a static buffer, so calling either one a
	// second time will overwrite previous results.
	//
	// The largest 32 bit integer is -2 billion plus null terminator, or 12 bytes.
	// Int should always be 32 bits on any remotely Unix-like system, see
	// http://www.unix.org/whitepapers/64bit.html for the reasons why.

	static char local_buf[12];

	// Convert unsigned integer to ascii using a static buffer (returned).
	char *utoa(unsigned n)
	{
	utoa_to_buf(n, local_buf, sizeof(local_buf));

	return local_buf;
	}

	// Convert signed integer to ascii using a static buffer (returned).
	char *itoa(int n)
	{
	itoa_to_buf(n, local_buf, sizeof(local_buf));

	return local_buf;
	}
	#endif

	#ifdef L_setuid
	// Die with an error message if we can't set gid. (Because resource limits may
	// limit this user to a given number of processes, and if that fills up the
	// setgid() will fail and we'll _still_be_root_, which is bad.)
	void xsetgid(gid_t gid)
	{
	if (setgid(gid)) bb_error_msg_and_die("setgid");
	}

	// Die with an error message if we cant' set uid. (See xsetgid() for why.)
	void xsetuid(uid_t uid)
	{
	if (setuid(uid)) bb_error_msg_and_die("setuid");
	}
	#endif

	#ifdef L_fdlength
	// Return how long the file at fd is, if there's any way to determine it.
	off_t fdlength(int fd)
	{
	off_t bottom = 0, top = 0, pos;
	long size;

	// If the ioctl works for this, return it.

	if (ioctl(fd, BLKGETSIZE, &size) >= 0) return size*512;

	// If not, do a binary search for the last location we can read. (Some
	// block devices don't do BLKGETSIZE right.)

	do {
	char temp;

	pos = bottom + (top - bottom) / 2;

	// If we can read from the current location, it's bigger.

	if (lseek(fd, pos, 0)>=0 && safe_read(fd, &temp, 1)==1) {
	if (bottom == top) bottom = top = (top+1) * 2;
	else bottom = pos;

	// If we can't, it's smaller.

	} else {
	if (bottom == top) {
	if (!top) return 0;
	bottom = top/2;
	}
	else top = pos;
	}
	} while (bottom + 1 != top);

	return pos + 1;
	}
	#endif

	#ifdef L_xasprintf
	// Die with an error message if we can't malloc() enough space and do an
	// sprintf() into that space.
	char xasprintf(const char format, ...)
	{
	va_list p;
	int r;
	char *string_ptr;

	#if 1
	// GNU extension
	va_start(p, format);
	r = vasprintf(&string_ptr, format, p);
	va_end(p);
	#else
	// Bloat for systems that haven't got the GNU extension.
	va_start(p, format);
	r = vsnprintf(NULL, 0, format, p);
	va_end(p);
	string_ptr = xmalloc(r+1);
	va_start(p, format);
	r = vsnprintf(string_ptr, r+1, format, p);
	va_end(p);
	#endif

	if (r < 0) bb_error_msg_and_die(bb_msg_memory_exhausted);
	return string_ptr;
	}
	#endif

	#ifdef L_xprint_and_close_file
	// Die with an error message if we can't copy an entire FILE * to stdout, then
	// close that file.
	void xprint_and_close_file(FILE *file)
	{
	// copyfd outputs error messages for us.
	if (bb_copyfd_eof(fileno(file), 1) == -1)
	exit(xfunc_error_retval);

	fclose(file);
	}
	#endif

	#ifdef L_xchdir
	// Die if we can't chdir to a new path.
	void xchdir(const char *path)
	{
	if (chdir(path))
	bb_perror_msg_and_die("chdir(%s)", path);
	}
	#endif

	#ifdef L_warn_opendir
	// Print a warning message if opendir() fails, but don't die.
	DIR warn_opendir(const char path)
	{
	DIR *dp;

	if ((dp = opendir(path)) == NULL) {
	bb_perror_msg("unable to open `%s'", path);
	return NULL;
	}
	return dp;
	}
	#endif

	#ifdef L_xopendir
	// Die with an error message if opendir() fails.
	DIR xopendir(const char path)
	{
	DIR *dp;

	if ((dp = opendir(path)) == NULL)
	bb_perror_msg_and_die("unable to open `%s'", path);
	return dp;
	}
	#endif

	#ifdef L_xdaemon
	#ifndef BB_NOMMU
	// Die with an error message if we can't daemonize.
	void xdaemon(int nochdir, int noclose)
	{
	if (daemon(nochdir, noclose)) bb_perror_msg_and_die("daemon");
	}
	#endif
	#endif

	#ifdef L_xsocket
	// Die with an error message if we can't open a new socket.
	int xsocket(int domain, int type, int protocol)
	{
	int r = socket(domain, type, protocol);

	if (r < 0) bb_perror_msg_and_die("socket");

	return r;
	}
	#endif

	#ifdef L_xbind
	// Die with an error message if we can't bind a socket to an address.
	void xbind(int sockfd, struct sockaddr *my_addr, socklen_t addrlen)
	{
	if (bind(sockfd, my_addr, addrlen)) bb_perror_msg_and_die("bind");
	}
	#endif

	#ifdef L_xlisten
	// Die with an error message if we can't listen for connections on a socket.
	void xlisten(int s, int backlog)
	{
	if (listen(s, backlog)) bb_perror_msg_and_die("listen");
	}
	#endif

	#ifdef L_xstat
	// xstat() - a stat() which dies on failure with meaningful error message
	void xstat(char name, struct stat stat_buf)
	{
	if (stat(name, stat_buf))
	bb_perror_msg_and_die("can't stat '%s'", name);
	}
	#endif

	#ifdef L_get_terminal_width_height
	/* It is perfectly ok to pass in a NULL for either width or for
	* * height, in which case that value will not be set. */
	int get_terminal_width_height(int fd, int width, int height)
	{
	struct winsize win = { 0, 0, 0, 0 };
	int ret = ioctl(fd, TIOCGWINSZ, &win);
	if (!win.ws_row) {
	char *s = getenv("LINES");
	if (s) win.ws_row = atoi(s);
	}
	if (win.ws_row <= 1) win.ws_row = 24;
	if (!win.ws_col) {
	char *s = getenv("COLUMNS");
	if (s) win.ws_col = atoi(s);
	}
	if (win.ws_col <= 1) win.ws_col = 80;
	if (height) *height = (int) win.ws_row;
	if (width) *width = (int) win.ws_col;

	return ret;
	}
	#endif