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

1 files changed, 4 insertions, 4 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 4d4843173..820fd888d 100644
--- a/shell/hush.c
+++ b/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 */