Commit 7050096d authored by Juergen Gross's avatar Juergen Gross
Browse files

xen/xenbus: add xenbus_setup_ring() service function 



Most PV device frontends share very similar code for setting up shared
ring buffers:

- allocate page(s)
- init the ring admin data
- give the backend access to the ring via grants

Tearing down the ring requires similar actions in all frontends again:

- remove grants
- free the page(s)

Provide service functions xenbus_setup_ring() and xenbus_teardown_ring()
for that purpose.

Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent 6fac592c

drivers/xen/xenbus/xenbus_client.c

+69 −0
Original line number Diff line number Diff line
@@ -407,6 +407,75 @@ int xenbus_grant_ring(struct xenbus_device *dev, void *vaddr, 
}

EXPORT_SYMBOL_GPL(xenbus_grant_ring);



/*

 * xenbus_setup_ring

 * @dev: xenbus device

 * @vaddr: pointer to starting virtual address of the ring

 * @nr_pages: number of pages to be granted

 * @grefs: grant reference array to be filled in

 *

 * Allocate physically contiguous pages for a shared ring buffer and grant it

 * to the peer of the given device. The ring buffer is initially filled with

 * zeroes. The virtual address of the ring is stored at @vaddr and the

 * grant references are stored in the @grefs array. In case of error @vaddr

 * will be set to NULL and @grefs will be filled with INVALID_GRANT_REF.

 */

int xenbus_setup_ring(struct xenbus_device *dev, gfp_t gfp, void **vaddr,

		      unsigned int nr_pages, grant_ref_t *grefs)

{

	unsigned long ring_size = nr_pages * XEN_PAGE_SIZE;

	unsigned int i;

	int ret;



	*vaddr = alloc_pages_exact(ring_size, gfp | __GFP_ZERO);

	if (!*vaddr) {

		ret = -ENOMEM;

		goto err;

	}



	ret = xenbus_grant_ring(dev, *vaddr, nr_pages, grefs);

	if (ret)

		goto err;



	return 0;



 err:

	if (*vaddr)

		free_pages_exact(*vaddr, ring_size);

	for (i = 0; i < nr_pages; i++)

		grefs[i] = INVALID_GRANT_REF;

	*vaddr = NULL;



	return ret;

}

EXPORT_SYMBOL_GPL(xenbus_setup_ring);



/*

 * xenbus_teardown_ring

 * @vaddr: starting virtual address of the ring

 * @nr_pages: number of pages

 * @grefs: grant reference array

 *

 * Remove grants for the shared ring buffer and free the associated memory.

 * On return the grant reference array is filled with INVALID_GRANT_REF.

 */

void xenbus_teardown_ring(void **vaddr, unsigned int nr_pages,

			  grant_ref_t *grefs)

{

	unsigned int i;



	for (i = 0; i < nr_pages; i++) {

		if (grefs[i] != INVALID_GRANT_REF) {

			gnttab_end_foreign_access(grefs[i], 0);

			grefs[i] = INVALID_GRANT_REF;

		}

	}



	if (*vaddr)

		free_pages_exact(*vaddr, nr_pages * XEN_PAGE_SIZE);

	*vaddr = NULL;

}

EXPORT_SYMBOL_GPL(xenbus_teardown_ring);



/**

 * Allocate an event channel for the given xenbus_device, assigning the newly

include/xen/xenbus.h

+4 −0
Original line number Diff line number Diff line
@@ -226,6 +226,10 @@ int xenbus_watch_pathfmt(struct xenbus_device *dev, struct xenbus_watch *watch, 
int xenbus_switch_state(struct xenbus_device *dev, enum xenbus_state new_state);

int xenbus_grant_ring(struct xenbus_device *dev, void *vaddr,

		      unsigned int nr_pages, grant_ref_t *grefs);

int xenbus_setup_ring(struct xenbus_device *dev, gfp_t gfp, void **vaddr,

		      unsigned int nr_pages, grant_ref_t *grefs);

void xenbus_teardown_ring(void **vaddr, unsigned int nr_pages,

			  grant_ref_t *grefs);

int xenbus_map_ring_valloc(struct xenbus_device *dev, grant_ref_t *gnt_refs,

			   unsigned int nr_grefs, void **vaddr);