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

Darrick J. Wong
2016-01-15T21:06:12Z

On Wed, Jan 13, 2016 at 12:25:26PM -0600, Eric Sandeen wrote:
> 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...

We certainly /could/ do that, but now the build depends on pahole or whatever
being installed, whereas this macroey doesn't add more tool dependencies.
I think between this and xfs/122 we're probably fine?

--D

>
> similar tricks could surely be done for userspace as well.
>
> -Eric
>
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