remove SWRITE* I/O types

These flags aren't real I/O types, but tell ll_rw_block to always
lock the buffer instead of giving up on a failed trylock.

Instead add a new write_dirty_buffer helper that implements this semantic
and use it from the existing SWRITE* callers.  Note that the ll_rw_block
code had a bug where it didn't promote WRITE_SYNC_PLUG properly, which
this patch fixes.

In the ufs code clean up the helper that used to call ll_rw_block
to mirror sync_dirty_buffer, which is the function it implements for
compound buffers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index f19ce94..2c4b1f1 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -1024,7 +1024,7 @@
 	if (wait)
 		sync_dirty_buffer(bh);
 	else
-		ll_rw_block(SWRITE, 1, &bh);
+		write_dirty_buffer(bh, WRITE);
 
 out:
 	/* If we have just flushed the log (by marking s_start==0), then