libbb: introduce and use nonblock_safe_read(). Yay!

Our shells are immune from this nasty O_NONBLOCK now!

function                                             old     new   delta
nonblock_safe_read                                     -      78     +78
file_get                                             276     295     +19
generateMTFValues                                    428     435      +7
read_line_input                                     1776    1772      -4
preadbuffer                                          543     450     -93
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/2 up/down: 104/-97)             Total: 7 bytes
   text    data     bss     dec     hex filename
 615190     715   23924  639829   9c355 busybox_old
 615168     715   23924  639807   9c33f busybox_unstripped

shell/ash.c

@@ -5428,7 +5428,7 @@ expbackq(union node *cmd, int quoted, int quotes)
  read:
 		if (in.fd < 0)
 			break;
-		i = safe_read(in.fd, buf, sizeof(buf));
+		i = nonblock_safe_read(in.fd, buf, sizeof(buf));
 		TRACE(("expbackq: read returns %d\n", i));
 		if (i <= 0)
 			break;
@@ -8678,7 +8678,7 @@ preadfd(void)
  retry:
 #if ENABLE_FEATURE_EDITING
 	if (!iflag || parsefile->fd)
-		nr = safe_read(parsefile->fd, buf, BUFSIZ - 1);
+		nr = nonblock_safe_read(parsefile->fd, buf, BUFSIZ - 1);
 	else {
 #if ENABLE_FEATURE_TAB_COMPLETION
 		line_input_state->path_lookup = pathval();
@@ -8700,9 +8700,11 @@ preadfd(void)
 		}
 	}
 #else
-	nr = safe_read(parsefile->fd, buf, BUFSIZ - 1);
+	nr = nonblock_safe_read(parsefile->fd, buf, BUFSIZ - 1);
 #endif
 
+#if 0
+/* nonblock_safe_read() handles this problem */
 	if (nr < 0) {
 		if (parsefile->fd == 0 && errno == EWOULDBLOCK) {
 			int flags = fcntl(0, F_GETFL);
@@ -8715,6 +8717,7 @@ preadfd(void)
 			}
 		}
 	}
+#endif
 	return nr;
 }
 
@@ -11801,7 +11804,7 @@ readcmd(int argc, char **argv)
 	backslash = 0;
 	STARTSTACKSTR(p);
 	do {
-		if (read(0, &c, 1) != 1) {
+		if (nonblock_safe_read(0, &c, 1) != 1) {
 			status = 1;
 			break;
 		}

shell/hush.c

@@ -1273,10 +1273,10 @@ static void get_user_input(struct in_str *i)
 	prompt_str = setup_prompt_string(i->promptmode);
 #if ENABLE_FEATURE_EDITING
 	/* Enable command line editing only while a command line
-	 * is actually being read; otherwise, we'll end up bequeathing
-	 * atexit() handlers and other unwanted stuff to our
-	 * child processes (rob@sysgo.de) */
-	r = read_line_input(prompt_str, user_input_buf, BUFSIZ-1, line_input_state);
+	 * is actually being read */
+	do {
+		r = read_line_input(prompt_str, user_input_buf, BUFSIZ-1, line_input_state);
+	} while (r == 0); /* repeat if Ctrl-C */
 	i->eof_flag = (r < 0);
 	if (i->eof_flag) { /* EOF/error detected */
 		user_input_buf[0] = EOF; /* yes, it will be truncated, it's ok */

shell/msh.c

@@ -42,6 +42,7 @@
 # define xmalloc(size) malloc(size)
 # define msh_main(argc,argv) main(argc,argv)
 # define safe_read(fd,buf,count) read(fd,buf,count)
+# define nonblock_safe_read(fd,buf,count) read(fd,buf,count)
 # define NOT_LONE_DASH(s) ((s)[0] != '-' || (s)[1])
 # define LONE_CHAR(s,c) ((s)[0] == (c) && !(s)[1])
 # define ATTRIBUTE_NORETURN __attribute__ ((__noreturn__))
@@ -3376,7 +3377,7 @@ static int doread(struct op *t)
 	}
 	for (wp = t->words + 1; *wp; wp++) {
 		for (cp = global_env.linep; !nl && cp < elinep - 1; cp++) {
-			nb = read(0, cp, sizeof(*cp));
+			nb = nonblock_safe_read(0, cp, sizeof(*cp));
 			if (nb != sizeof(*cp))
 				break;
 			nl = (*cp == '\n');
@@ -4799,7 +4800,7 @@ static int filechar(struct ioarg *ap)
 			if (i)
 				lseek(ap->afile, ap->afpos, SEEK_SET);
 
-			i = safe_read(ap->afile, bp->buf, sizeof(bp->buf));
+			i = nonblock_safe_read(ap->afile, bp->buf, sizeof(bp->buf));
 			if (i <= 0) {
 				closef(ap->afile);
 				return 0;
@@ -4830,7 +4831,7 @@ static int filechar(struct ioarg *ap)
 		return c;
 	}
 #endif
-	i = safe_read(ap->afile, &c, sizeof(c));
+	i = nonblock_safe_read(ap->afile, &c, sizeof(c));
 	return i == sizeof(c) ? (c & 0x7f) : (closef(ap->afile), 0);
 }
 
@@ -4841,7 +4842,7 @@ static int herechar(struct ioarg *ap)
 {
 	char c;
 
-	if (read(ap->afile, &c, sizeof(c)) != sizeof(c)) {
+	if (nonblock_safe_read(ap->afile, &c, sizeof(c)) != sizeof(c)) {
 		close(ap->afile);
 		c = '\0';
 	}