xen/granttable: Improve comments for function pointers

/*This is a structure of function pointers for grant table*/

struct gnttab_ops {

	/*

	 * Mapping a list of frames for storing grant entries. First input

	 * parameter is used to storing grant table address when grant table

	 * being setup, second parameter is the number of frames to map grant

	 * table. Returning GNTST_okay means success and negative value means

	 * failure.

	 * Mapping a list of frames for storing grant entries. Frames parameter

	 * is used to store grant table address when grant table being setup,

	 * nr_gframes is the number of frames to map grant table. Returning

	 * GNTST_okay means success and negative value means failure.

	 */

	int (*map_frames)(unsigned long *, unsigned int);

	int (*map_frames)(unsigned long *frames, unsigned int nr_gframes);

	/*

	 * Release a list of frames which are mapped in map_frames for grant

	 * entry status.

	 */

	void (*unmap_frames)(void);

	/*

	 * Introducing a valid entry into the grant table, granting the frame

	 * of this grant entry to domain for accessing, or transfering, or

	 * transitively accessing. First input parameter is reference of this

	 * introduced grant entry, second one is domid of granted domain, third

	 * one is the frame to be granted, and the last one is status of the

	 * grant entry to be updated.

	 * Introducing a valid entry into the grant table, granting the frame of

	 * this grant entry to domain for accessing or transfering. Ref

	 * parameter is reference of this introduced grant entry, domid is id of

	 * granted domain, frame is the page frame to be granted, and flags is

	 * status of the grant entry to be updated.

	 */

	void (*update_entry)(grant_ref_t, domid_t, unsigned long, unsigned);

	void (*update_entry)(grant_ref_t ref, domid_t domid,

			     unsigned long frame, unsigned flags);

	/*

	 * Stop granting a grant entry to domain for accessing. First input

	 * parameter is reference of a grant entry whose grant access will be

	 * stopped, second one is not in use now. If the grant entry is

	 * Stop granting a grant entry to domain for accessing. Ref parameter is

	 * reference of a grant entry whose grant access will be stopped,

	 * readonly is not in use in this function. If the grant entry is

	 * currently mapped for reading or writing, just return failure(==0)

	 * directly and don't tear down the grant access. Otherwise, stop grant

	 * access for this entry and return success(==1).

	 */

	int (*end_foreign_access_ref)(grant_ref_t, int);

	int (*end_foreign_access_ref)(grant_ref_t ref, int readonly);

	/*

	 * Stop granting a grant entry to domain for transfer. If tranfer has

	 * not started, just reclaim the grant entry and return failure(==0).

	 * Otherwise, wait for the transfer to complete and then return the

	 * frame.

	 * Stop granting a grant entry to domain for transfer. Ref parameter is

	 * reference of a grant entry whose grant transfer will be stopped. If

	 * tranfer has not started, just reclaim the grant entry and return

	 * failure(==0). Otherwise, wait for the transfer to complete and then

	 * return the frame.

	 */

	unsigned long (*end_foreign_transfer_ref)(grant_ref_t);

	unsigned long (*end_foreign_transfer_ref)(grant_ref_t ref);

	/*

	 * Query the status of a grant entry. Input parameter is reference of

	 * Query the status of a grant entry. Ref parameter is reference of

	 * queried grant entry, return value is the status of queried entry.

	 * Detailed status(writing/reading) can be gotten from the return value

	 * by bit operations.

	 */

	int (*query_foreign_access)(grant_ref_t);

	int (*query_foreign_access)(grant_ref_t ref);

};

static struct gnttab_ops *gnttab_interface;