On Wed, 26 Jul 2000, Jamie Lokier wrote:
>
> 1. Make the name explicit: inode->i_union->bdev.
>
> 2. Change all the code that refers to the newly unioned fields.
> It should be clear from the name i_union that no code should
> read a field until it knows the type of the inode.
>
> 3. Do something similar for struct page. At least that would
> remove the ugly overloading of page->next_hash fields on the Sparc.
I hate unions that have to do it this way.
Unions are imho only acceptable when they implicitly know their own type.
The in-kernel example of this is the inode per-filesystem thing. An inode
has a filesystem-specific part, and there is no way any other filesystem
can access it except by a major bug somewhere.
Any union that needs code like
if (xxx->type == yyy)..
....
is a design mistake.
I don't think you'll find all that many unions in Linux. And I don't think
we should add new ones..
Linus
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