Re: Compatibility issue with 2.2.19pre7

[Manfred <manfred@colorfullife.com>]

Zitiere Russell King <rmk@arm.linux.org.uk>:
> The API changed:
>  struct nfs_mount_data {
>         int             version;                /* 1 */
>         int             fd;                     /* 1 */
> -       struct nfs_fh   root;                   /* 1 */
> +       struct nfs2_fh  old_root;               /* 1 */

I don't see an API change:
the 2.2.17 "struct nfs_fs" and the 2.2.18 "struct nfs2_fh" are identical.

Ok, I see the problem:

struct nfs_fh {
    unsigned short          size;
    unsigned char           data[NFS_MAXFHSIZE];
}

The compiler thinks that data is a character array, thus no padding is inserted.
nlm_lookup_file casts f->data to "struct knfs_fs", a structure with pointers and
u32. --> unaligned u32 read --> boom.

Is that correct?
Is &(((struct nfs_fh*)0)->data) 2 or 4?

ARM isn't the only cpu that can't handle unaligned memory reads, why doesn't the
code fail on Alpha/Sparc? Does gcc insert padding on these cpus?


--
	Manfred
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