On Wed, Mar 29, 2023 at 11:41 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> + struct iovec __ubuf_iovec;
I think this is the third time I say this: this should be "const struct iovec".
No other use is ever valid, and this cast:
> +static inline const struct iovec *iter_iov(const struct iov_iter *iter)
> +{
> + if (iter->iter_type == ITER_UBUF)
> + return (const struct iovec *) &iter->__ubuf_iovec;
should simply not exist.
The first rule of cast club is that casting one pointer to another is
generally a sign that something is wrong.
Casting a pointer to an integer? That's a valid way to get at the bit
representation for things like tagged pointers or for virtual address
arithmetic etc (ok, and by "valid" I mean "valid in kernel contexts -
not necessarily in all other contexts).
Casting an integer to a pointer? Same thing - some things just need to
do bit operations on what will become a pointer (allocators etc).
But casting a pointer to another one - that should basically always
raise eyebrows. You should try really hard to avoid it.
Yes, we do it in the kernel, and yes, it *can* be valid. But most of
the time it's really a bad sign.
Linus
