Claude review: dma-buf: Add dma_buf_mapping_attach()

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

> +	struct dma_buf_mapping_match sgt_match[] = {
> +		DMA_BUF_IMAPPING_SGT(dev, importer_ops->allow_peer2peer ?
> +						  DMA_SGT_IMPORTER_ACCEPTS_P2P :
> +						  DMA_SGT_NO_P2P),
> +	};

In the new `dma_buf_dynamic_attach`, `importer_ops->allow_peer2peer` is dereferenced without a NULL check. The original code had `if (importer_ops)` before accessing this field. Currently all callers of `dma_buf_dynamic_attach` pass non-NULL `importer_ops` (the NULL case is handled by the separate `dma_buf_attach` wrapper), but the original API contract allowed NULL. If any future caller passes NULL, this will crash. Consider adding a `WARN_ON(!importer_ops)` guard or updating the documentation to indicate `importer_ops` is now required.

> +	if (WARN_ON(!dmabuf))
> +		return ERR_PTR(-EINVAL);

The check for `!dev` was removed since the device is now embedded in match data. But `dma_buf_mapping_attach` doesn't validate that the importer provided a non-NULL device in their match entries either. For SGT, a NULL `importing_dma_device` would propagate to `dma_map_sgtable()` calls, causing a crash there rather than at attach time.

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