diff --git a/coreutils/tee.c b/coreutils/tee.c
index 06c94aba6..640a231ef 100644
--- a/coreutils/tee.c
+++ b/coreutils/tee.c
@@ -17,67 +17,66 @@ int tee_main(int argc, char **argv)
 {
 	const char *mode = "w\0a";
 	FILE **files;
-	FILE **p;
-	char **filenames;
+	FILE **fp;
+	char **names;
+	char **np;
 	int flags;
 	int retval = EXIT_SUCCESS;
-#ifdef CONFIG_FEATURE_TEE_USE_BLOCK_IO
+#if ENABLE_FEATURE_TEE_USE_BLOCK_IO
 	ssize_t c;
 # define buf bb_common_bufsiz1
 #else
 	int c;
 #endif
-
 	flags = getopt32(argc, argv, "ia");	/* 'a' must be 2nd */
+	argc -= optind;
+	argv += optind;
 
 	mode += (flags & 2);	/* Since 'a' is the 2nd option... */
 
 	if (flags & 1) {
-		signal(SIGINT, SIG_IGN);	/* TODO - switch to sigaction.*/
+		signal(SIGINT, SIG_IGN); /* TODO - switch to sigaction. */
 	}
-
 	/* gnu tee ignores SIGPIPE in case one of the output files is a pipe
 	 * that doesn't consume all its input.  Good idea... */
-	signal(SIGPIPE, SIG_IGN);	/* TODO - switch to sigaction.*/
+	signal(SIGPIPE, SIG_IGN);	/* TODO - switch to sigaction. */
 
 	/* Allocate an array of FILE *'s, with one extra for a sentinal. */
-	p = files = (FILE **)xmalloc(sizeof(FILE *) * (argc - optind + 2));
-	*p = stdout;
-	argv += optind - 1;
-	filenames = argv - 1;
-	*filenames = (char *) bb_msg_standard_input;	/* for later */
-	goto GOT_NEW_FILE;
+	fp = files = xzalloc(sizeof(FILE *) * (argc + 2));
+	np = names = argv - 1;
 
+	files[0] = stdout;
+	goto GOT_NEW_FILE;
 	do {
-		if ((*p = fopen_or_warn(*argv, mode)) == NULL) {
+		*fp = fopen_or_warn(*argv, mode);
+		if (*fp == NULL) {
 			retval = EXIT_FAILURE;
 			continue;
 		}
-		filenames[(int)(p - files)] = *argv;
-	GOT_NEW_FILE:
-		setbuf(*p, NULL);	/* tee must not buffer output. */
-		++p;
-	} while (*++argv);
+		*np = *argv++;
+ GOT_NEW_FILE:
+		setbuf(*fp++, NULL);	/* tee must not buffer output. */
+		np++;
+	} while (*argv);
+	/* names[0] will be filled later */
 
-	*p = NULL;				/* Store the sentinal value. */
-
-#ifdef CONFIG_FEATURE_TEE_USE_BLOCK_IO
+#if ENABLE_FEATURE_TEE_USE_BLOCK_IO
 	while ((c = safe_read(STDIN_FILENO, buf, BUFSIZ)) > 0) {
-		for (p=files ; *p ; p++) {
-			fwrite(buf, 1, c, *p);
-		}
+		fp = files;
+		do
+			fwrite(buf, 1, c, *fp++);
+		while (*fp);
 	}
-
-	if (c < 0) {			/* Make sure read errors are signaled. */
+	if (c < 0) {		/* Make sure read errors are signaled. */
 		retval = EXIT_FAILURE;
 	}
-
 #else
 	setvbuf(stdout, NULL, _IONBF, 0);
 	while ((c = getchar()) != EOF) {
-		for (p=files ; *p ; p++) {
-			putc(c, *p);
-		}
+		fp = files;
+		do
+			putc(c, *fp++);
+		while (*fp);
 	}
 #endif
 
@@ -87,14 +86,15 @@ int tee_main(int argc, char **argv)
 	 * setting the first entry to stdin and checking stdout error
 	 * status with fflush_stdout_and_exit()... although fflush()ing
 	 * is unnecessary here. */
-
-	p = files;
-	*p = stdin;
-	do {		/* Now check for (input and) output errors. */
+	np = names;
+	fp = files;
+	names[0] = (char *) bb_msg_standard_input;
+	files[0] = stdin;
+	do {	/* Now check for input and output errors. */
 		/* Checking ferror should be sufficient, but we may want to fclose.
 		 * If we do, remember not to close stdin! */
-		die_if_ferror(*p, filenames[(int)(p - files)]);
-	} while (*++p);
+		die_if_ferror(*fp++, *np++);
+	} while (*fp);
 
 	fflush_stdout_and_exit(retval);
 }
diff --git a/include/libbb.h b/include/libbb.h
index 5cba27932..61e379423 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -271,7 +271,7 @@ extern void *xmalloc_open_read_close(const char *filename, size_t *sizep);
 
 extern ssize_t safe_write(int fd, const void *buf, size_t count);
 extern ssize_t full_write(int fd, const void *buf, size_t count);
-extern void xwrite(int fd, void *buf, size_t count);
+extern void xwrite(int fd, const void *buf, size_t count);
 
 /* Reads and prints to stdout till eof, then closes FILE. Exits on error: */
 extern void xprint_and_close_file(FILE *file);
diff --git a/libbb/copyfd.c b/libbb/copyfd.c
index 601c51ce4..c6b886647 100644
--- a/libbb/copyfd.c
+++ b/libbb/copyfd.c
@@ -25,37 +25,50 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
 {
 	int status = -1;
 	off_t total = 0;
-	RESERVE_CONFIG_BUFFER(buffer,BUFSIZ);
+	RESERVE_CONFIG_BUFFER(buffer, BUFSIZ);
 
 	if (src_fd < 0) goto out;
-	while (!size || total < size) {
-		ssize_t wr, rd;
 
-		rd = safe_read(src_fd, buffer,
-				(!size || size - total > BUFSIZ) ? BUFSIZ : size - total);
+	if (!size) {
+		size = BUFSIZ;
+		status = 1; /* copy until eof */
+	}
 
-		if (rd > 0) {
-			/* A -1 dst_fd means we need to fake it... */
-			wr = (dst_fd < 0) ? rd : full_write(dst_fd, buffer, rd);
+	while (1) {
+		ssize_t rd;
+
+		rd = safe_read(src_fd, buffer, size > BUFSIZ ? BUFSIZ : size);
+
+		if (!rd) { /* eof - all done. */
+			status = 0;
+			break;
+		}
+		if (rd < 0) {
+			bb_perror_msg(bb_msg_read_error);
+			break;
+		}
+		/* dst_fd == -1 is a fake, else... */
+		if (dst_fd >= 0) {
+			ssize_t wr = full_write(dst_fd, buffer, rd);
 			if (wr < rd) {
 				bb_perror_msg(bb_msg_write_error);
 				break;
 			}
-			total += wr;
-			if (total == size) status = 0;
-		} else if (rd < 0) {
-			bb_perror_msg(bb_msg_read_error);
-			break;
-		} else { /* eof - all done. */
-			status = 0;
-			break;
+		}
+		total += rd;
+		if (status < 0) {
+			size -= rd;
+			if (!size) {
+				status = 0;
+				break;
+			}
 		}
 	}
 
 out:
 	RELEASE_CONFIG_BUFFER(buffer);
 
-	return status ? status : total;
+	return status ? -1 : total;
 }
 
 
diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
index 1dbd7521b..773e718b8 100644
--- a/libbb/xfuncs.c
+++ b/libbb/xfuncs.c
@@ -124,7 +124,7 @@ int ndelay_on(int fd)
 }
 
 // Die with an error message if we can't write the entire buffer.
-void xwrite(int fd, void *buf, size_t count)
+void xwrite(int fd, const void *buf, size_t count)
 {
 	if (count) {
 		ssize_t size = full_write(fd, buf, count);
@@ -146,7 +146,7 @@ off_t xlseek(int fd, off_t offset, int whence)
 void die_if_ferror(FILE *fp, const char *fn)
 {
 	if (ferror(fp)) {
-		bb_error_msg_and_die("%s", fn);
+		bb_error_msg_and_die("%s: I/O error", fn);
 	}
 }