pnfs-obj: Return PNFS_NOT_ATTEMPTED in case of read/write_pagelist

objlayout driver was always returning PNFS_ATTEMPTED from it's
read/write_pagelist operations. Even on error. Fix that.

Start by establishing an error return API from io-engine, by
not returning ssize_t (length-or-error) but returning "int"
0=OK, 0>Error. And clean up all return types in io-engine.

Then if io-engine returned error return PNFS_NOT_ATTEMPTED
to generic layer. (With a dprint)

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/objlayout/objlayout.h b/fs/nfs/objlayout/objlayout.h
index ffb884c6..4edac9b 100644
--- a/fs/nfs/objlayout/objlayout.h
+++ b/fs/nfs/objlayout/objlayout.h
@@ -115,8 +115,8 @@
 	gfp_t gfp_flags);
 extern void objio_free_io_state(struct objlayout_io_state *state);
 
-extern ssize_t objio_read_pagelist(struct objlayout_io_state *ol_state);
-extern ssize_t objio_write_pagelist(struct objlayout_io_state *ol_state,
+extern int objio_read_pagelist(struct objlayout_io_state *ol_state);
+extern int objio_write_pagelist(struct objlayout_io_state *ol_state,
 				    bool stable);
 
 /*