Re: [PATCH] xfs: check sizes of XFS on-disk structures at compile time

Eric Sandeen
2016-01-13T18:25:34Z

On 1/11/16 5:26 PM, Darrick J. Wong wrote:

> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 36bd882..31b69d1 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1812,11 +1812,56 @@ xfs_destroy_workqueues(void)
> destroy_workqueue(xfs_alloc_wq);
> }
>
> +static void __init
> +xfs_check_ondisk_structs(void)
> +{
> + /* on-disk structures */
> + XFS_CHECK_STRUCT_SIZE(struct xfs_dsb, 264);
> + XFS_CHECK_STRUCT_SIZE(struct xfs_agf, 224);
> + XFS_CHECK_STRUCT_SIZE(struct xfs_agi, 336);
> + XFS_CHECK_STRUCT_SIZE(struct xfs_agfl, 36);
> + XFS_CHECK_STRUCT_SIZE(struct xfs_timestamp, 8);
> + XFS_CHECK_STRUCT_SIZE(struct xfs_dinode, 176);

I'm not sure why, but all this hard-coded stuff in the codebase bugs me.

What if we did it as part of the build, but outside the code, something
like (pardon my bad Make-fu):

diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index f646391..da9ec6d 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -122,3 +122,8 @@ xfs-$(CONFIG_XFS_POSIX_ACL) += xfs_acl.o
xfs-$(CONFIG_SYSCTL) += xfs_sysctl.o
xfs-$(CONFIG_COMPAT) += xfs_ioctl32.o
xfs-$(CONFIG_NFSD_PNFS) += xfs_pnfs.o
+
+check_structures: $(obj)/xfs.o
+ $(src)/scripts/check_structures.sh $(obj)/xfs.o
+
+$(obj)/built-in.o: check_structures

where the script executes pahole or whatever we want, to check the
structure sizes and possibly even alignment explicitly? Presumably
we could make running the check a Kconfig option as well...

similar tricks could surely be done for userspace as well.

-Eric