Re: [PATCH] introduce grant copy for user land

[David Vrabel <david.vrabel@citrix.com>]

On 02/10/14 16:15, Thanos Makatos wrote:
> This patch introduces the interface to allow user-space applications
> execute grant-copy operations. This is done by sending an ioctl to the
> grant device. The number of grant-copy segments is currently limited to
> 16 in order to simplify the implementation, however the ABI allows an
> arbitrary number of operations.

Sorry for not responding earlier.  If I haven't responded to a patch in
a week, a reminder ping is appreciated.

The arbitrary limitations in number of ops and page alignment should be
removed.  I think both can be removed relatively easily by consuming
page aligned chunks of segments and doign the hypercall when a batch of
ops is filled.

> +struct gntdev_grant_copy_segment {
> +	/*
> +	 * source address and length
> +	 */
> +	struct iovec iov;
> +
> +	/* the granted page */
> +	uint32_t ref;
> +
> +	/* offset in the granted page */
> +	uint16_t offset;
> +
> +	/* grant copy result (GNTST_XXX) */
> +	int16_t status;
> +};
> +
> +#define IOCTL_GNTDEV_GRANT_COPY \
> +_IOC(_IOC_NONE, 'G', 8, sizeof(struct ioctl_gntdev_grant_copy))
> +struct ioctl_gntdev_grant_copy {
> +	/*
> +	 * copy direction: 0 to copy to guest, 1 to copy from guest
> +	 */
> +	int dir;

I think this dir should be per-segment and use the GNTCPY_source_gref
and GNTCOPY_dest_gref flags, since per-op direction is what the
hypercall provides.

> +
> +	/* domain ID */
> +	uint32_t domid;
> +
> +	unsigned int count;
> +
> +	struct gntdev_grant_copy_segment __user *segments;
> +};

David