Subject: [PATCH] ext2: propagate volume-open errors when probing the superblock

open_volume() returns a negative errno on failure. Negating rc, which is
still zero, makes fsim_get_ext2_superblock() report success without reading
or validating the superblock. fs_probe() then accepts the volume as Ext4.

Return the positive error code from fd, as expected by the FSIM interface.

diff --git a/plugins/ext2/fsimext2.c b/plugins/ext2/fsimext2.c
index a30448c..d18fd66 100644
--- a/plugins/ext2/fsimext2.c
+++ b/plugins/ext2/fsimext2.c
@@ -523,7 +523,7 @@ int fsim_get_ext2_superblock( logical_volume_t *volume, struct ext2_super_block
 
 	fd = EngFncs->open_volume(volume, O_RDONLY, 0);
 	if (fd < 0) {
-		rc = -rc;
+		rc = -fd;
 		LOG_EXIT_INT(rc);
 		return rc;
 	}