/******************************************************************************
- * arch/xen/drivers/blkif/backend/main.c
*
* Back-end of the driver for virtual block devices. This portion of the
* driver exports a 'unified' block-device interface that can be accessed
* by any operating system that implements a compatible front end. A
* reference front-end implementation can be found in:
- * arch/xen/drivers/blkif/frontend
+ * drivers/block/xen-blkfront.c
*
* Copyright (c) 2003-2004, Keir Fraser & Steve Hand
* Copyright (c) 2005, Christopher Clark
#define BLKBACK_INVALID_HANDLE (~0)
struct xen_blkbk {
- pending_req_t *pending_reqs;
+ pending_req_t *pending_reqs;
+ /* List of all 'pending_req' available */
struct list_head pending_free;
+ /* And its spinlock. */
spinlock_t pending_free_lock;
wait_queue_head_t pending_free_wq;
+ /* The list of all pages that are available. */
struct page **pending_pages;
+ /* And the grant handles that are available. */
grant_handle_t *pending_grant_handles;
};
static struct xen_blkbk *blkbk;
+/*
+ * Little helpful macro to figure out the index and virtual address of the
+ * pending_pages[..]. For each 'pending_req' we have have up to
+ * BLKIF_MAX_SEGMENTS_PER_REQUEST (11) pages. The seg would be from 0 through
+ * 10 and would index in the pending_pages[..]. */
static inline int vaddr_pagenr(pending_req_t *req, int seg)
{
return (req - blkbk->pending_reqs) * BLKIF_MAX_SEGMENTS_PER_REQUEST + seg;
static void make_response(blkif_t *blkif, u64 id,
unsigned short op, int st);
-/******************************************************************
- * misc small helpers
+/*
+ * Retrieve from the 'pending_reqs' a free pending_req structure to be used.
*/
static pending_req_t* alloc_req(void)
{
return req;
}
+/*
+ * Return the 'pending_req' structure back to the freepool. We also
+ * wake up the thread if it was waiting for a free page.
+ */
static void free_req(pending_req_t *req)
{
unsigned long flags;
wake_up(&blkbk->pending_free_wq);
}
+/*
+ * Give back a reference count on the underlaying storage.
+ * It is OK to make multiple calls in this function as it
+ * resets the plug to NULL when it is done on the first call.
+ */
static void unplug_queue(blkif_t *blkif)
{
if (blkif->plug == NULL)
blkif->plug = NULL;
}
+/*
+ * Take a reference count on the underlaying storage.
+ * It is OK to call this multiple times as we check to make sure
+ * not to double reference. We also give back a reference count
+ * if it corresponds to another queue.
+ */
static void plug_queue(blkif_t *blkif, struct block_device *bdev)
{
struct request_queue *q = bdev_get_queue(bdev);
blkif->plug = q;
}
+/*
+ * Unmap the grant references, and also remove the M2P over-rides
+ * used in the 'pending_req'.
+*/
static void fast_flush_area(pending_req_t *req)
{
struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
return 0;
}
-/******************************************************************
- * COMPLETION CALLBACK -- Called as bh->b_end_io()
+/*
+ * Completion callback on the bio's. Called as bh->b_end_io()
*/
static void __end_block_io_op(pending_req_t *pending_req, int error)
pending_req->status = BLKIF_RSP_ERROR;
}
+ /* If all of the bio's have completed it is time to unmap
+ * the grant references associated with 'request' and provide
+ * the proper response on the ring. */
if (atomic_dec_and_test(&pending_req->pendcnt)) {
fast_flush_area(pending_req);
make_response(pending_req->blkif, pending_req->id,
}
}
+/*
+ * bio callback.
+ */
static void end_block_io_op(struct bio *bio, int error)
{
__end_block_io_op(bio->bi_private, error);
}
-/******************************************************************************
- * NOTIFICATION FROM GUEST OS.
+/*
+ * Notification from the guest OS.
*/
static void blkif_notify_work(blkif_t *blkif)
-/******************************************************************
- * DOWNWARD CALLS -- These interface with the block-device layer proper.
+/*
+ * Function to copy the from the ring buffer the 'struct blkif_request'
+ * (which has the sectors we want, number of them, grant references, etc),
+ * and transmute it to the block API to hand it over to the proper block disk.
*/
-
static int do_block_io_op(blkif_t *blkif)
{
union blkif_back_rings *blk_rings = &blkif->blk_rings;
return more_to_do;
}
+/*
+ * Transumation of the 'struct blkif_request' to a proper 'struct bio'
+ * and call the 'submit_bio' to pass it to the underlaying storage.
+ */
static void dispatch_rw_block_io(blkif_t *blkif,
struct blkif_request *req,
pending_req_t *pending_req)
BUG();
}
- /* Check that number of segments is sane. */
+ /* Check that the number of segments is sane. */
nseg = req->nr_segments;
if (unlikely(nseg == 0 && operation != WRITE_BARRIER) ||
unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
pending_req->status = BLKIF_RSP_OKAY;
pending_req->nr_pages = nseg;
+ /* Fill out preq.nr_sects with proper amount of sectors, and setup
+ * assign map[..] with the PFN of the page in our domain with the
+ * corresponding grant reference for each page.*/
for (i = 0; i < nseg; i++) {
uint32_t flags;
seg[i].nsec = req->u.rw.seg[i].last_sect -
req->u.rw.seg[i].first_sect + 1;
-
if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
(req->u.rw.seg[i].last_sect < req->u.rw.seg[i].first_sect))
goto fail_response;
ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, nseg);
BUG_ON(ret);
+ /* Now swizzel the MFN in our domain with the MFN from the other domain
+ * so that when we access vaddr(pending_req,i) it has the contents of the
+ * page from the other domain. */
for (i = 0; i < nseg; i++) {
if (unlikely(map[i].status != 0)) {
DPRINTK("invalid buffer -- could not remap it\n");
if (ret) {
printk(KERN_ALERT "Failed to install M2P override for"\
" %lx (ret: %d)\n", (unsigned long)map[i].dev_bus_addr, ret);
+ /* We could switch over to GNTTABOP_copy */
continue;
}
(req->u.rw.seg[i].first_sect << 9);
}
+ /* If we have failed at this point, we need to undo the M2P override, set
+ * gnttab_set_unmap_op on all of the grant references and perform the
+ * hypercall to unmap the grants - that is all done in fast_flush_area. */
if (ret)
goto fail_flush;
goto fail_flush;
}
+ /* Get a reference count for the disk queue and start sending I/O */
plug_queue(blkif, preq.bdev);
+
+ /* We set it one so that the last submit_bio does not have to call
+ * atomic_inc. */
atomic_set(&pending_req->pendcnt, 1);
blkif_get(blkif);
atomic_inc(&pending_req->pendcnt);
submit_bio(operation, bio);
}
-
+
bio = bio_alloc(GFP_KERNEL, nseg-i);
if (unlikely(bio == NULL))
goto fail_put_bio;
preq.sector_number += seg[i].nsec;
}
+ /* This will be hit if the operation was a barrier. */
if (!bio) {
BUG_ON(operation != WRITE_BARRIER);
bio = bio_alloc(GFP_KERNEL, 0);
-/******************************************************************
- * MISCELLANEOUS SETUP / TEARDOWN / DEBUGGING
+/*
+ * Put a response on the ring on how the operation fared.
*/
-
-
static void make_response(blkif_t *blkif, u64 id,
unsigned short op, int st)
{
git.openpandora.org / pandora-kernel.git / commitdiff