xfs: create xfs_bmap_util.[ch]

There is a bunch of code in xfs_bmap.c that is kernel specific and
not shared with userspace. To minimise the difference between the
kernel and userspace code, shift this unshared code to
xfs_bmap_util.c, and the declarations to xfs_bmap_util.h.

The biggest issue here is xfs_bmap_finish() - userspace has it's own
definition of this function, and so we need to move it out of
xfs_bmap.[ch]. This means several other files need to include
xfs_bmap_util.h as well.

It also introduces and interesting dance for the stack switching
code in xfs_bmapi_allocate(). The stack switching/workqueue code is
actually moved to xfs_bmap_util.c, so that userspace can simply use
a #define in a header file to connect the dots without needing to
know about the stack switch code at all.

Signed-off-by: Dave Chinner <[email protected]>
Reviewed-by: Mark Tinguely <[email protected]>
Signed-off-by: Ben Myers <[email protected]>

fs/xfs/Makefile

@@ -30,6 +30,7 @@ xfs-y				+= xfs_aops.o \
 				   xfs_attr_inactive.o \
 				   xfs_attr_list.o \
 				   xfs_bit.o \
+				   xfs_bmap_util.o \
 				   xfs_buf.o \
 				   xfs_dfrag.o \
 				   xfs_dir2_readdir.o \

fs/xfs/xfs_aops.c

@@ -31,6 +31,7 @@
 #include "xfs_vnodeops.h"
 #include "xfs_trace.h"
 #include "xfs_bmap.h"
+#include "xfs_bmap_util.h"
 #include <linux/aio.h>
 #include <linux/gfp.h>
 #include <linux/mpage.h>

fs/xfs/xfs_attr.c

@@ -33,6 +33,7 @@
 #include "xfs_alloc.h"
 #include "xfs_inode_item.h"
 #include "xfs_bmap.h"
+#include "xfs_bmap_util.h"
 #include "xfs_attr.h"
 #include "xfs_attr_leaf.h"
 #include "xfs_attr_remote.h"

fs/xfs/xfs_attr_remote.c

@@ -34,6 +34,7 @@
 #include "xfs_alloc.h"
 #include "xfs_inode_item.h"
 #include "xfs_bmap.h"
+#include "xfs_bmap_util.h"
 #include "xfs_attr.h"
 #include "xfs_attr_leaf.h"
 #include "xfs_attr_remote.h"