From: blaisorblade_spam@yahoo.it

Currently, ubd=sync is different from replacing ubd#= with ubd#s=. This is
against Principle of Least Surprise, so remove this difference.

Also the current ubd=sync behaviour is completely useless: it is to make sure
that when the kernel has synched its I/O to the virtual disk, the host does
not invalidate this with his caching; this causes ReiserFS corruption.

But since actually we call end_request() only after the io_thread has done its
work, we never lie to the block layer. Using O_SYNC as we do when replacing
ubd#= with ubd#s= is enough.

Also merged uml-ubd-thread-start-fail-well:

Correct the failure path in start_io_thread(), to return the correct
error code.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

 um-linux-2.4.27-paolo/arch/um/drivers/ubd_kern.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff -puN arch/um/drivers/ubd_kern.c~ubd-use-io-thread-always arch/um/drivers/ubd_kern.c
--- um-linux-2.4.27/arch/um/drivers/ubd_kern.c~ubd-use-io-thread-always	2005-04-15 11:13:09.000000000 +0200
+++ um-linux-2.4.27-paolo/arch/um/drivers/ubd_kern.c	2005-04-15 11:13:09.000000000 +0200
@@ -708,18 +708,20 @@ int ubd_init(void)
 	for(i=0;i<MAX_DEV;i++)
 		ubd_add(i);
 
+	/* Set by CONFIG_BLK_DEV_UBD_SYNC or ubd=sync.*/
 	if(global_openflags.s){
-		printk(KERN_INFO "ubd : Synchronous mode\n");
-		return(0);
+		printk(KERN_INFO "ubd: Synchronous mode\n");
+		/* Letting ubd=sync be like using ubd#s= instead of ubd#= is
+		 * enough. So use anyway the io thread. */
 	}
 	stack = alloc_stack(0, 0);
 	io_pid = start_io_thread(stack + PAGE_SIZE - sizeof(void *),
 				 &thread_fd);
 	if(io_pid < 0){
-		io_pid = -1;
 		printk(KERN_ERR
 		       "ubd : Failed to start I/O thread (errno = %d) - "
 		       "falling back to synchronous I/O\n", -io_pid);
+		io_pid = -1;
 		return(0);
 	}
 	err = um_request_irq(UBD_IRQ, thread_fd, IRQ_READ, ubd_intr,
_