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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: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2022-04-28 09:01:03 +02:00
parent 6fac592cca
commit 7050096d07
2 changed files with 73 additions and 0 deletions
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69
drivers/xen/xenbus/xenbus_client.c
View File

@ -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

4
include/xen/xenbus.h
View File

@ -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);