uml: random driver fixes

The random driver would essentially hang if the host's /dev/random returned
-EAGAIN. There was a test of need_resched followed by a schedule inside the
loop, but that didn't help and it's the wrong way to work anyway.

The right way is to ask for an interrupt when there is input available from
the host and handle it then rather than polling.

Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup
when there's randomness available again and sleeps. The interrupt routine
just wakes up whatever processes are sleeping on host_read_wait.

There is an atomic_t, host_sleep_count, which counts the number of processes
waiting for randomness. When this reaches zero, the interrupt is disabled.

An added complication is that async I/O notification was only recently added
to /dev/random (by me), so essentially all hosts will lack it. So, we use the
sigio workaround here, which is to have a separate thread poll on the
descriptor and send an interrupt when there is input on it. This mechanism is
activated when a process gets -EAGAIN (activating this multiple times is
harmless, if a bit wasteful) and deactivated by the last process still
waiting.

The module name was changed from "random" to "hw_random" in order for udev to
recognize it.

The sigio workaround needed some changes. sigio_broken was added for cases
when we know that async notification doesn't work. This is now called from
maybe_sigio_broken, which deals with pts devices.

Signed-off-by: Jeff Dike <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/um/drivers/random.c

···
 #include <linux/sched.h>
 #include <linux/module.h>
 #include <linux/fs.h>
+#include <linux/interrupt.h>
 #include <linux/miscdevice.h>
 #include <linux/delay.h>
 #include <asm/uaccess.h>
+#include "irq_kern.h"
 #include "os.h"
 
 /*
  * core module and version information
  */
 #define RNG_VERSION "1.0.0"
-#define RNG_MODULE_NAME "random"
+#define RNG_MODULE_NAME "hw_random"
 
 #define RNG_MISCDEV_MINOR		183 /* official */
 
···
  * protects against a module being loaded twice at the same time.
  */
 static int random_fd = -1;
+static DECLARE_WAIT_QUEUE_HEAD(host_read_wait);
 
 static int rng_dev_open (struct inode *inode, struct file *filp)
 {
···
 
 	return 0;
 }
+
+static atomic_t host_sleep_count = ATOMIC_INIT(0);
 
 static ssize_t rng_dev_read (struct file *filp, char __user *buf, size_t size,
                              loff_t * offp)
···
                         }
                 }
                 else if(n == -EAGAIN){
+			DECLARE_WAITQUEUE(wait, current);
+
                         if (filp->f_flags & O_NONBLOCK)
                                 return ret ? : -EAGAIN;
 
-                        if(need_resched())
-                                schedule_timeout_interruptible(1);
+			atomic_inc(&host_sleep_count);
+			reactivate_fd(random_fd, RANDOM_IRQ);
+			add_sigio_fd(random_fd);
+
+			add_wait_queue(&host_read_wait, &wait);
+			set_task_state(current, TASK_INTERRUPTIBLE);
+
+			schedule();
+			set_task_state(current, TASK_RUNNING);
+			remove_wait_queue(&host_read_wait, &wait);
+
+			if (atomic_dec_and_test(&host_sleep_count)) {
+				ignore_sigio_fd(random_fd);
+				deactivate_fd(random_fd, RANDOM_IRQ);
+			}
                 }
                 else return n;
 		if (signal_pending (current))
···
 	&rng_chrdev_ops,
 };
 
+static irqreturn_t random_interrupt(int irq, void *data)
+{
+	wake_up(&host_read_wait);
+
+	return IRQ_HANDLED;
+}
+
 /*
  * rng_init - initialize RNG module
  */
···
 
         random_fd = err;
 
-        err = os_set_fd_block(random_fd, 0);
+	err = um_request_irq(RANDOM_IRQ, random_fd, IRQ_READ, random_interrupt,
+			     IRQF_DISABLED | IRQF_SAMPLE_RANDOM, "random",
+			     NULL);
         if(err)
 		goto err_out_cleanup_hw;
+
+	sigio_broken(random_fd, 1);
 
 	err = misc_register (&rng_miscdev);
 	if (err) {
···
         return err;
 
  err_out_cleanup_hw:
+	os_close_file(random_fd);
         random_fd = -1;
         goto out;
 }
···
  */
 static void __exit rng_cleanup (void)
 {
+	os_close_file(random_fd);
 	misc_deregister (&rng_miscdev);
 }
 

arch/um/include/os.h

···
 extern int add_sigio_fd(int fd);
 extern int ignore_sigio_fd(int fd);
 extern void maybe_sigio_broken(int fd, int read);
+extern void sigio_broken(int fd, int read);
 
 /* sys-x86_64/prctl.c */
 extern int os_arch_prctl(int pid, int code, unsigned long *addr);

arch/um/include/process.h

···
 /* 
- * Copyright (C) 2000, 2001, 2002 Jeff Dike ([e-mail])
+ * Copyright (C) 2000 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */
 
···
 
 #include <signal.h>
 
+/* Copied from linux/compiler-gcc.h since we can't include it directly */
+#define barrier() __asm__ __volatile__("": : :"memory")
+
 extern void sig_handler(int sig, struct sigcontext sc);
 extern void alarm_handler(int sig, struct sigcontext sc);
 
 #endif
-
-/*
- * Overrides for Emacs so that we follow Linus's tabbing style.
- * Emacs will notice this stuff at the end of the file and automatically
- * adjust the settings for this buffer only.  This must remain at the end
- * of the file.
- * ---------------------------------------------------------------------------
- * Local variables:
- * c-file-style: "linux"
- * End:
- */

arch/um/os-Linux/sigio.c

···
 /*
- * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2002 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */
 
···
 #include "kern_util.h"
 #include "init.h"
 #include "os.h"
+#include "process.h"
 #include "sigio.h"
 #include "um_malloc.h"
 #include "user.h"
···
 	close(l_write_sigio_fds[1]);
 }
 
-/* Changed during early boot */
-static int pty_output_sigio = 0;
-static int pty_close_sigio = 0;
-
-void maybe_sigio_broken(int fd, int read)
+void sigio_broken(int fd, int read)
 {
 	int err;
-
-	if (!isatty(fd))
-		return;
-
-	if ((read || pty_output_sigio) && (!read || pty_close_sigio))
-		return;
 
 	write_sigio_workaround();
 
···
 	sigio_unlock();
 }
 
+/* Changed during early boot */
+static int pty_output_sigio;
+static int pty_close_sigio;
+
+void maybe_sigio_broken(int fd, int read)
+{
+	if (!isatty(fd))
+		return;
+
+	if ((read || pty_output_sigio) && (!read || pty_close_sigio))
+		return;
+
+	sigio_broken(fd, read);
+}
+
 static void sigio_cleanup(void)
 {
 	if (write_sigio_pid == -1)
···
 __uml_exitcall(sigio_cleanup);
 
 /* Used as a flag during SIGIO testing early in boot */
-static volatile int got_sigio = 0;
+static int got_sigio;
 
 static void __init handler(int sig)
 {
···
 	if (errno != EAGAIN)
 		printk(UM_KERN_ERR "tty_output : write failed, errno = %d\n",
 		       errno);
-	while (((n = read(slave, buf, sizeof(buf))) > 0) && !got_sigio)
+	while (((n = read(slave, buf, sizeof(buf))) > 0) &&
+	       !({ barrier(); got_sigio; }))
 		;
 
 	if (got_sigio) {

include/asm-um/irq.h

···
 #define SIGIO_WRITE_IRQ 	11
 #define TELNETD_IRQ 		12
 #define XTERM_IRQ 		13
+#define RANDOM_IRQ 		14
 
-#define LAST_IRQ XTERM_IRQ
+#define LAST_IRQ RANDOM_IRQ
 #define NR_IRQS (LAST_IRQ + 1)
 
 #endif