libposix: add support for O_NONBLOCK

We keep a list of non blocking fds and use awake to
make them not block on read, write, pread and pwrite.

qa/lib/newlib/104-files-nonblocking.c

@@ -0,0 +1,110 @@
+// C program to illustrate
+// non I/O blocking calls
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h> // library for fcntl function
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/types.h>
+
+#define MSGSIZE 6
+char* msg1 ="hello";
+char* msg2 ="bye !!";
+ 
+void parent_read(int p[])
+{
+	int nread;
+	char buf[MSGSIZE];
+ 
+	// write link
+	close(p[1]);
+ 
+	while (1) {
+ 
+		// read call if return -1 then pipe is
+		// empty because of fcntl
+		nread = read(p[0], buf, MSGSIZE);
+		switch (nread) {
+		case -1:
+ 
+			// case -1 means pipe is empty and errono
+			// set EAGAIN
+			if (errno == EAGAIN) {
+				printf("(pipe empty)\n");
+				sleep(1);
+				break;
+			}
+ 
+			else {
+				perror("read");
+				exit(4);
+			}
+ 
+		// case 0 means all bytes are read and EOF(end of conv.)
+		case 0:
+			printf("End of conversation\n");
+ 
+			// read link
+			close(p[0]);
+ 
+			exit(0);
+		default:
+ 
+			// text read
+			// by default return no. of bytes
+			// which read call read at that time
+			printf("MSG = %s\n", buf);
+		}
+	}
+}
+void child_write(int p[])
+{
+	int i;
+ 
+	// read link
+	close(p[0]);
+ 
+	// write 3 times "hello" in 3 second interval
+	for (i = 0; i < 3; i++) {
+		write(p[1], msg1, MSGSIZE);
+		sleep(3);
+	}
+ 
+	// write "bye" one times
+	write(p[1], msg2, MSGSIZE);
+ 
+	// here after write all bytes then write end
+	// doesn't close so read end block but
+	// because of fcntl block doesn't happen..
+	exit(0);
+}
+int main()
+{
+	int p[2];
+ 
+	// error checking for pipe
+	if (pipe(p) < 0)
+		exit(1);
+ 
+	// error checking for fcntl
+	if (fcntl(p[0], F_SETFL, O_NONBLOCK) < 0)
+		exit(2);
+ 
+	// continued
+	switch (fork()) {
+ 
+	// error
+	case -1:
+		exit(3);
+ 
+	// 0 for child process
+	case 0:
+		child_write(p);
+		break;
+ 
+	default:
+		parent_read(p);
+		break;
+	}
+	return 0;
+}