tarfs: Fix the size of struct tarfs_fid and add a static assert

File system specific *fid structures are copied into the generic
struct fid defined in sys/mount.h.
As such, they cannot be larger than struct fid.

This patch packs the structure and checks via a __Static_assert().

Reviewed by:	markj
MFC after:	2 weeks

2 files changed, 3 insertions, 1 deletions

diff --git a/sys/fs/tarfs/tarfs.h b/sys/fs/tarfs/tarfs.h
index ff1985e488cd..ffb95d2c0ac5 100644
--- a/sys/fs/tarfs/tarfs.h
+++ b/sys/fs/tarfs/tarfs.h
@@ -165,7 +165,7 @@ struct tarfs_fid {
 	u_short			 data0;	/* force alignment */
 	ino_t			 ino;
 	unsigned long		 gen;
-};
+} __packed;
 
 #define	TARFS_NODE_LOCK(tnp) \
 	mtx_lock(&(tnp)->lock)
diff --git a/sys/fs/tarfs/tarfs_vnops.c b/sys/fs/tarfs/tarfs_vnops.c
index 8c97fab185fc..afb8e05f5929 100644
--- a/sys/fs/tarfs/tarfs_vnops.c
+++ b/sys/fs/tarfs/tarfs_vnops.c
@@ -668,6 +668,8 @@ tarfs_vptofh(struct vop_vptofh_args *ap)
 {
 	struct tarfs_fid *tfp;
 	struct tarfs_node *tnp;
+	_Static_assert(sizeof(struct tarfs_fid) <= sizeof(struct fid),
+	    "struct tarfs_fid cannot be larger than struct fid");
 
 	tfp = (struct tarfs_fid *)ap->a_fhp;
 	tnp = VP_TO_TARFS_NODE(ap->a_vp);