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, 7 insertions, 4 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 65f94f682..debe8ecdd 100644
--- a/shell/ash.c
+++ b/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;
                 }