[PATCH] PowerPC: honor O_NONBLOCK flag for rtas error_log

[Vitaly Mayatskikh <v.mayatskih@gmail.com>]

rtas_log_read() currently doesn't count O_NONBLOCK flag. This sample
code will block on read:

  fd = open ("/proc/ppc64/rtas/error_log", O_RDONLY | O_NONBLOCK);
  while (1) {
    err =read (fd, buf, 4096);
    printf("err = %d, errno = %d (%s)\n", err, errno, strerror(errno));
    sleep(1);
  }

With patched kernel it produces such (correct) output:

err = 2052, errno = 0 (Success)
err = -1, errno = 11 (Resource temporarily unavailable)
err = -1, errno = 11 (Resource temporarily unavailable)
err = -1, errno = 11 (Resource temporarily unavailable)
err = -1, errno = 11 (Resource temporarily unavailable)

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>

diff --git a/arch/powerpc/platforms/pseries/rtasd.c b/arch/powerpc/platforms/pseries/rtasd.c
index 7d3e2b0..f530f68 100644
--- a/arch/powerpc/platforms/pseries/rtasd.c
+++ b/arch/powerpc/platforms/pseries/rtasd.c
@@ -291,22 +291,25 @@ static ssize_t rtas_log_read(struct file * file, char __user * buf,
 	if (!access_ok(VERIFY_WRITE, buf, count))
 		return -EFAULT;
 
-	tmp = kmalloc(count, GFP_KERNEL);
-	if (!tmp)
-		return -ENOMEM;
-
-
 	spin_lock_irqsave(&rtasd_log_lock, s);
 	/* if it's 0, then we know we got the last one (the one in NVRAM) */
-	if (rtas_log_size == 0 && logging_enabled)
+	if (rtas_log_size == 0 && logging_enabled) {
 		nvram_clear_error_log();
+		if (file->f_flags & O_NONBLOCK) {
+			spin_unlock_irqrestore(&rtasd_log_lock, s);
+			return -EAGAIN;
+		}
+	}
 	spin_unlock_irqrestore(&rtasd_log_lock, s);
 
-
 	error = wait_event_interruptible(rtas_log_wait, rtas_log_size);
 	if (error)
 		goto out;
 
+	tmp = kmalloc(count, GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+
 	spin_lock_irqsave(&rtasd_log_lock, s);
 	offset = rtas_error_log_buffer_max * (rtas_log_start & LOG_NUMBER_MASK);
 	memcpy(tmp, &rtas_log_buf[offset], count);

-- 
wbr, Vitaly