Re: Enlarging w/ xfs_growfs: XFS_IOC_FSGROWFSDATA xfsctl failed: Inappropriate ioctl for device

Dave Chinner
2018-12-13T21:39:25Z

On Wed, Dec 12, 2018 at 11:49:36PM -0500, Nick Bowler wrote:
> On 2018-12-12, Nick Bowler <nbowler@draconx.ca> wrote:
> > On 2018-12-12, Dave Chinner <david@fromorbit.com> wrote:
> >> On Tue, Dec 11, 2018 at 11:56:33PM -0500, Nick Bowler wrote:
> >>> OK, xfstests has revealed some trouble with the three "bulkstat" ioctls,
> >>> since while the xfs_bulkstat structure itself is fine, one of its
> >>> members
> >>> is used as a pointer to various structures which are not fine. This
> >>> wasn't too hard to fix though.
> >>
> >> IIRC, there's bigger problems than you realise here - the bulkstat
> >> structure has embedded timestamps in them and on x32 struct timeval
> >> doesn't match either ia32 or x86-64. i.e. on ia32, struct timeval is
> >> 8 bytes, on x86-64 it is 16 bytes, and in x32 it is 12 bytes.
> >
> > This is not the case: struct timeval is 16 bytes on x32:
> >
> > sizeof (struct timeval): 16
> > tv_sec size: 8 offset: 0
> > tv_usec size: 8 offset: 8

I was just quoting the kernel time subsystem maintainer who
said that these structures had problems with size and packing.

> >
> > This is the same as what I get on native 64-bit compilations; but
> > anyway the xfs_bstat structure has xfs_bstime members, with the
> > following characteristics on x32:
> >
> > sizeof (struct xfs_bstime): 16
> > tv_sec size: 8 offset: 0
> > tv_nsec size: 4 offset: 8
> >
> > which is also the same as native 64-bit (time_t is the same on x32 and
> > native: 8 bytes with 8 byte alignment).
> >
> > I manually verified every member of the xfs_bstat structure with sizeof
> > and offsetof on -mx32 and -m64 compilations to ensure that this structure
> > matches precisely between the x32 and native 64-bit cases.
>
> To expand on this, for each structure which my RFC patchset feeds up to
> the native handler, I first checked them by manual inspection and then
> double checked using the following program; we can compile with both
> -mx32 and -m64 and check that the output is identical.

So, turn that into an xfstest so that it is always run, diffs the
output between compat/native depending on which one is used complete
with guards that break the test when we add a new ioctl. We already
we have a test that is for explicitly checking that structures on disk
are the same for 32/64 bit architectures: tests/xfs/122

That test automates the generation of the test code and output,
and if it changes from the golden output, then the test fails.
I'd suggest that a similar thing is done here for /all/ the
structures we expose in ioctls.

FWIW, pahole can make this easy. e.g you can harvest every ioctl
structure from xfs_fs.h, write them into a file like so:

$ cat t.c
#include <xfs/xfs.h>

/* these should be the same for x32/x86-64, but not i386 */
int main(int argc, char *argv[])
{
struct xfs_bstat bs = {0};
struct xfs_fsop_geom_v1 geo1 = {0};
struct xfs_fsop_geom geo = {0};
struct xfs_growfs_data gd = {0};
struct xfs_growfs_rt gr = {0};
struct xfs_flock64 fl = {0};
struct xfs_inogrp ig = {0};
struct xfs_swapext se = {0};

return 0;
}

And then compile and dump the structure layouts like so:
$ gcc -m64 -gdwarf-2 t.c -c; pahole t.o > t.x86-64
$ gcc -mx32 -gdwarf-2 t.c -c; pahole t.o > t.x32
$ gcc -m32 -gdwarf-2 t.c -c; pahole t.o > t.i386

Then we'll have tests that will fail if we ever change an ioctl or
add a new one and don't add it to the test. That guarantees we won't
ever forget about this....

Cheers,

Dave.

--
Dave Chinner
david@fromorbit.com