[ Sorry, David, if you get this multiple times. Had a doh! moment... ]
On Fri, 2005-01-21 at 14:47 -0800, David S. Miller wrote:
> On Thu, 30 Dec 2004 03:48:35 -0500
> David Dillow <dave@xxxxxxxxxxxxxx> wrote:
> > +static inline struct xfrm_offload *
> > +xfrm_offload_alloc(int sizeof_priv, struct net_device *dev)
> This whole scheme looks buggy. The intent is to 8-byte align
> the object, but look at what the code is actually doing.
> Whatever kmalloc() returns to xfrm_offload_alloc() is directly
> used as the xfrm_offload pointer, and the members are initialized.
> Then xfrm_offload_priv() does the alignments.
Right, I'm not worried about the alignment of the xfrm_offload, as I'm
assuming that kmalloc will give us something suitable. However, I do
want to make sure that the private section used by the driver is 8 byte
aligned in the face of a potentially oddly sized xfrm_offload struct.
Am I making a bad assumption that kmalloc() will give me a suitable
alignment for the base struct?
> It is clear that kmalloc() is always giving you 8-byte aligned
> data else the first time xfrm_offload_priv() is used you'd
> get a bogus pointer since xfrm_offload_alloc() initialized
> the object without first aligning the pointer.
The driver calls xfrm_offload_alloc(), then calls xfrm_offload_priv() to
get it's private struct, and inits that. I just want to make sure the
private struct is 8 byte aligned, which I assume (wrongly?) will be
sufficient to prevent misaligned accesses.
> We do something similar when we allocate netdevs, so have a look
> at how net/core/dev.c:alloc_netdev() works.
I copied part of that code to xfrm_offload_alloc(), removing the part
that aligned the base xfrm_offload struct. 32 byte alignment seemed a
bit much, do you think it is needed? I'll be happy to add that if you
David Dillow <dave@xxxxxxxxxxxxxx>