sh: Improve error handling in read builtin:

* If read -t times out, return status as if interrupted by SIGALRM
  (formerly 1).
* If a trapped signal interrupts read, return status 128+sig (formerly 1).
* If [EINTR] occurs but there is no trap, retry the read (for example
  because of a SIGWINCH in interactive mode).
* If a read error occurs, write an error message and return status 2.

As before, a variable assignment error returns 2 and discards the remaining
data read.

bin/sh/miscbltin.c

@@ -60,6 +60,7 @@ __FBSDID("$FreeBSD$");
 #include "error.h"
 #include "mystring.h"
 #include "syntax.h"
+#include "trap.h"
 
 #undef eflag
 
@@ -102,6 +103,8 @@ readcmd(int argc __unused, char **argv __unused)
 	struct timeval tv;
 	char *tvptr;
 	fd_set ifds;
+	ssize_t nread;
+	int sig;
 
 	rflag = 0;
 	prompt = NULL;
@@ -156,8 +159,10 @@ readcmd(int argc __unused, char **argv __unused)
 		/*
 		 * If there's nothing ready, return an error.
 		 */
-		if (status <= 0)
-			return(1);
+		if (status <= 0) {
+			sig = pendingsig;
+			return (128 + (sig != 0 ? sig : SIGALRM));
+		}
 	}
 
 	status = 0;
@@ -165,7 +170,19 @@ readcmd(int argc __unused, char **argv __unused)
 	backslash = 0;
 	STARTSTACKSTR(p);
 	for (;;) {
-		if (read(STDIN_FILENO, &c, 1) != 1) {
+		nread = read(STDIN_FILENO, &c, 1);
+		if (nread == -1) {
+			if (errno == EINTR) {
+				sig = pendingsig;
+				if (sig == 0)
+					continue;
+				status = 128 + sig;
+				break;
+			}
+			warning("read error: %s", strerror(errno));
+			status = 2;
+			break;
+		} else if (nread != 1) {
 			status = 1;
 			break;
 		}

bin/sh/sh.1

@@ -32,7 +32,7 @@
 .\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
 .\" $FreeBSD$
 .\"
-.Dd April 21, 2013
+.Dd May 3, 2013
 .Dt SH 1
 .Os
 .Sh NAME
@@ -2372,7 +2372,9 @@ option is specified and the
 elapses before a complete line of input is supplied,
 the
 .Ic read
-command will return an exit status of 1 without assigning any values.
+command will return an exit status as if terminated by
+.Dv SIGALRM
+without assigning any values.
 The
 .Ar timeout
 value may optionally be followed by one of
@@ -2388,6 +2390,11 @@ is assumed.
 The
 .Fl e
 option exists only for backward compatibility with older scripts.
+.Pp
+The exit status is 0 on success, 1 on end of file,
+between 2 and 128 if an error occurs
+and greater than 128 if a trapped signal interrupts
+.Ic read .
 .It Ic readonly Oo Fl p Oc Op Ar name ...
 Each specified
 .Ar name

tools/regression/bin/sh/builtins/read7.0

@@ -0,0 +1,5 @@
+# $FreeBSD$
+
+{ errmsg=`read x <&- 2>&1 >&3`; } 3>&1
+r=$?
+[ "$r" -ge 2 ] && [ "$r" -le 128 ] && [ -n "$errmsg" ]

tools/regression/bin/sh/builtins/read8.0

@@ -0,0 +1,13 @@
+# $FreeBSD$
+
+T=`mktemp -d ${TMPDIR:-/tmp}/sh-test.XXXXXX`
+trap 'rm -rf $T' 0
+cd $T || exit 3
+mkfifo fifo1
+trapped=
+trap trapped=1 QUIT
+{ kill -QUIT $$; sleep 1; exit 4; } >fifo1 &
+read dummy <fifo1
+r=$?
+kill $!
+[ "$r" -gt 128 ] && [ -n "$trapped" ]