Re: NFSD binary compatibility breakage

[Neil Brown]

On Tuesday April 8, [e-mail] wrote:
> Neil,
> 
> The removal of "struct nfsctl_uidmap" from "nfsctl_fdparm" broke
> binary compatiblity on 64-bit platforms (strictly speaking: on all
> platforms with alignof(void *) > alignof(int)).  The problem is that
> nfsctl_uidmap contained a "char *", which forced the alignment of the
> entire union to be 64 bits.  With the removal of the uidmap, the
> required alignment drops to 32 bits.  Since the first member is only
> 32 bits in size, this breaks compatibility with user-space.  Patch
> below fixes the problem.

Hmm... just another reason to get rid of these binary interfaces!  I
plan to rip them all out in 2.7.1.  But for now I'll try to keep them
going as best I can.  Thanks for the patch.

NeilBrown

> 
> Thanks,
> 
> 	--david
> 
> ===== include/linux/nfsd/syscall.h 1.4 vs edited =====
> --- 1.4/include/linux/nfsd/syscall.h	Sun Mar 23 14:35:20 2003
> +++ edited/include/linux/nfsd/syscall.h	Tue Apr  8 22:36:59 2003
> @@ -91,6 +91,13 @@
>  		struct nfsctl_export	u_export;
>  		struct nfsctl_fdparm	u_getfd;
>  		struct nfsctl_fsparm	u_getfs;
> +		/*
> +		 * The following dummy member is needed to preserve binary compatibility
> +		 * on platforms where alignof(void*)>alignof(int).  It's needed because
> +		 * this union used to contain a member (u_umap) which contained a
> +		 * pointer.
> +		 */
> +		void *u_ptr;
>  	} u;
>  #define ca_svc		u.u_svc
>  #define ca_client	u.u_client