[patch] direct-io: propagate -ENOSPC errors

[Jeff Moyer <jmoyer@redhat.com>]

dio_bio_complete turns all errors into -EIO.  This is historical,
since you used to only get 1 bit precision for errors (BIO_UPTODATE).
Now that we get actual error codes, we can return the appropriate
code to userspace.  File systems seem to only propagate either EIO
or ENOSPC, so I've followed suit in this patch.

This fixes an issue where -ENOSPC was being turned into -EIO when
testing dm-thin.

Reported-by: Carlos Maiolino <cmaiolin@redhat.com>
Tested-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

diff --git a/fs/direct-io.c b/fs/direct-io.c
index d6a9012..990e0aa 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -466,13 +466,15 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio)
 {
 	struct bio_vec *bvec;
 	unsigned i;
-	int err;
 
-	if (bio->bi_error)
+	/* Only EIO and ENOSPC should be returned to userspace. */
+	if (bio->bi_error == 0 ||
+	    bio->bi_error == -ENOSPC || bio->bi_error == -EIO)
+		dio->io_error = bio->bi_error;
+	else
 		dio->io_error = -EIO;
 
 	if (dio->is_async && dio->rw == READ && dio->should_dirty) {
-		err = bio->bi_error;
 		bio_check_pages_dirty(bio);	/* transfers ownership */
 	} else {
 		bio_for_each_segment_all(bvec, bio, i) {
@@ -483,10 +485,9 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio)
 				set_page_dirty_lock(page);
 			page_cache_release(page);
 		}
-		err = bio->bi_error;
 		bio_put(bio);
 	}
-	return err;
+	return dio->io_error;
 }
 
 /*