shell: improve bash compatibility of read built-in

Make the read built-in more compatible with bash:

- Return an exit code of 142 on timeout.

- When the timeout expires before a newline is detected in the
  input bash captures the partial input.  This behaviour is new
  since bash version 4.4.  BusyBox shells had the pre-4.4 behaviour
  where the input was lost.

Update the tests to suit and fix a couple of compiler errors in
the testsuite.

function                                             old     new   delta
builtin_read                                         154     174     +20
readcmd                                              213     228     +15
shell_builtin_read                                  1364    1370      +6
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 41/0)               Total: 41 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/shell/shell_common.c b/shell/shell_common.c
index e5c2cefb3..9a03f7265 100644
--- a/shell/shell_common.c
+++ b/shell/shell_common.c
@@ -204,8 +204,8 @@ shell_builtin_read(struct builtin_read_params *params)
                          * 32-bit unix time wrapped (year 2038+).
                          */
                         if (timeout <= 0) { /* already late? */
-                                retval = (const char *)(uintptr_t)1;
-                                goto ret;
+                                retval = (const char *)(uintptr_t)2;
+                                break;
                         }
                 }
 
@@ -217,8 +217,12 @@ shell_builtin_read(struct builtin_read_params *params)
                 pfd[0].events = POLLIN;
 //TODO race with a signal arriving just before the poll!
                 if (poll(pfd, 1, timeout) <= 0) {
-                        /* timed out, or EINTR */
+                        /* timed out, or some error */
                         err = errno;
+                        if (!err) {
+                                retval = (const char *)(uintptr_t)2;
+                                break;
+                        }
                         retval = (const char *)(uintptr_t)1;
                         goto ret;
                 }