my solution to lab5

lab/user/testfdsharing.c

@@ -0,0 +1,38 @@
+#include <inc/x86.h>
+#include <inc/lib.h>
+
+char buf[512], buf2[512];
+
+void
+umain(int argc, char **argv)
+{
+	int fd, r, n, n2;
+
+	if ((fd = open("motd", O_RDONLY)) < 0)
+		panic("open motd: %e", fd);
+	seek(fd, 0);
+	if ((n = readn(fd, buf, sizeof buf)) <= 0)
+		panic("readn: %e", n);
+
+	if ((r = fork()) < 0)
+		panic("fork: %e", r);
+	if (r == 0) {
+		seek(fd, 0);
+		cprintf("going to read in child (might page fault if your sharing is buggy)\n");
+		if ((n2 = readn(fd, buf2, sizeof buf2)) != n)
+			panic("read in parent got %d, read in child got %d", n, n2);
+		if (memcmp(buf, buf2, n) != 0)
+			panic("read in parent got different bytes from read in child");
+		cprintf("read in child succeeded\n");
+		seek(fd, 0);
+		close(fd);
+		exit();
+	}
+	wait(r);
+	if ((n2 = readn(fd, buf2, sizeof buf2)) != n)
+		panic("read in parent got %d, then got %d", n, n2);
+	cprintf("read in parent succeeded\n");
+	close(fd);
+
+	breakpoint();
+}