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ubuntu-linux-kernel/drivers/block/xen-blkback/blkback.c

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2024-04-01 15:06:58 +00:00
/******************************************************************************
*
* 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:
* drivers/block/xen-blkfront.c
*
* Copyright (c) 2003-2004, Keir Fraser & Steve Hand
* Copyright (c) 2005, Christopher Clark
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation; or, when distributed
* separately from the Linux kernel or incorporated into other
* software packages, subject to the following license:
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this source file (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy, modify,
* merge, publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#define pr_fmt(fmt) "xen-blkback: " fmt
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/delay.h>
#include <linux/freezer.h>
#include <linux/bitmap.h>
#include <xen/events.h>
#include <xen/page.h>
#include <xen/xen.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>
#include <xen/balloon.h>
#include <xen/grant_table.h>
#include "common.h"
/*
* Maximum number of unused free pages to keep in the internal buffer.
* Setting this to a value too low will reduce memory used in each backend,
* but can have a performance penalty.
*
* A sane value is xen_blkif_reqs * BLKIF_MAX_SEGMENTS_PER_REQUEST, but can
* be set to a lower value that might degrade performance on some intensive
* IO workloads.
*/
static int xen_blkif_max_buffer_pages = 1024;
module_param_named(max_buffer_pages, xen_blkif_max_buffer_pages, int, 0644);
MODULE_PARM_DESC(max_buffer_pages,
"Maximum number of free pages to keep in each block backend buffer");
/*
* Maximum number of grants to map persistently in blkback. For maximum
* performance this should be the total numbers of grants that can be used
* to fill the ring, but since this might become too high, specially with
* the use of indirect descriptors, we set it to a value that provides good
* performance without using too much memory.
*
* When the list of persistent grants is full we clean it up using a LRU
* algorithm.
*/
static int xen_blkif_max_pgrants = 1056;
module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644);
MODULE_PARM_DESC(max_persistent_grants,
"Maximum number of grants to map persistently");
/*
* Maximum number of rings/queues blkback supports, allow as many queues as there
* are CPUs if user has not specified a value.
*/
unsigned int xenblk_max_queues;
module_param_named(max_queues, xenblk_max_queues, uint, 0644);
MODULE_PARM_DESC(max_queues,
"Maximum number of hardware queues per virtual disk." \
"By default it is the number of online CPUs.");
/*
* Maximum order of pages to be used for the shared ring between front and
* backend, 4KB page granularity is used.
*/
unsigned int xen_blkif_max_ring_order = XENBUS_MAX_RING_GRANT_ORDER;
module_param_named(max_ring_page_order, xen_blkif_max_ring_order, int, S_IRUGO);
MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring");
/*
* The LRU mechanism to clean the lists of persistent grants needs to
* be executed periodically. The time interval between consecutive executions
* of the purge mechanism is set in ms.
*/
#define LRU_INTERVAL 100
/*
* When the persistent grants list is full we will remove unused grants
* from the list. The percent number of grants to be removed at each LRU
* execution.
*/
#define LRU_PERCENT_CLEAN 5
/* Run-time switchable: /sys/module/blkback/parameters/ */
static unsigned int log_stats;
module_param(log_stats, int, 0644);
#define BLKBACK_INVALID_HANDLE (~0)
/* Number of free pages to remove on each call to gnttab_free_pages */
#define NUM_BATCH_FREE_PAGES 10
static inline int get_free_page(struct xen_blkif_ring *ring, struct page **page)
{
unsigned long flags;
spin_lock_irqsave(&ring->free_pages_lock, flags);
if (list_empty(&ring->free_pages)) {
BUG_ON(ring->free_pages_num != 0);
spin_unlock_irqrestore(&ring->free_pages_lock, flags);
return gnttab_alloc_pages(1, page);
}
BUG_ON(ring->free_pages_num == 0);
page[0] = list_first_entry(&ring->free_pages, struct page, lru);
list_del(&page[0]->lru);
ring->free_pages_num--;
spin_unlock_irqrestore(&ring->free_pages_lock, flags);
return 0;
}
static inline void put_free_pages(struct xen_blkif_ring *ring, struct page **page,
int num)
{
unsigned long flags;
int i;
spin_lock_irqsave(&ring->free_pages_lock, flags);
for (i = 0; i < num; i++)
list_add(&page[i]->lru, &ring->free_pages);
ring->free_pages_num += num;
spin_unlock_irqrestore(&ring->free_pages_lock, flags);
}
static inline void shrink_free_pagepool(struct xen_blkif_ring *ring, int num)
{
/* Remove requested pages in batches of NUM_BATCH_FREE_PAGES */
struct page *page[NUM_BATCH_FREE_PAGES];
unsigned int num_pages = 0;
unsigned long flags;
spin_lock_irqsave(&ring->free_pages_lock, flags);
while (ring->free_pages_num > num) {
BUG_ON(list_empty(&ring->free_pages));
page[num_pages] = list_first_entry(&ring->free_pages,
struct page, lru);
list_del(&page[num_pages]->lru);
ring->free_pages_num--;
if (++num_pages == NUM_BATCH_FREE_PAGES) {
spin_unlock_irqrestore(&ring->free_pages_lock, flags);
gnttab_free_pages(num_pages, page);
spin_lock_irqsave(&ring->free_pages_lock, flags);
num_pages = 0;
}
}
spin_unlock_irqrestore(&ring->free_pages_lock, flags);
if (num_pages != 0)
gnttab_free_pages(num_pages, page);
}
#define vaddr(page) ((unsigned long)pfn_to_kaddr(page_to_pfn(page)))
static int do_block_io_op(struct xen_blkif_ring *ring);
static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
struct blkif_request *req,
struct pending_req *pending_req);
static void make_response(struct xen_blkif_ring *ring, u64 id,
unsigned short op, int st);
#define foreach_grant_safe(pos, n, rbtree, node) \
for ((pos) = container_of(rb_first((rbtree)), typeof(*(pos)), node), \
(n) = (&(pos)->node != NULL) ? rb_next(&(pos)->node) : NULL; \
&(pos)->node != NULL; \
(pos) = container_of(n, typeof(*(pos)), node), \
(n) = (&(pos)->node != NULL) ? rb_next(&(pos)->node) : NULL)
/*
* We don't need locking around the persistent grant helpers
* because blkback uses a single-thread for each backend, so we
* can be sure that this functions will never be called recursively.
*
* The only exception to that is put_persistent_grant, that can be called
* from interrupt context (by xen_blkbk_unmap), so we have to use atomic
* bit operations to modify the flags of a persistent grant and to count
* the number of used grants.
*/
static int add_persistent_gnt(struct xen_blkif_ring *ring,
struct persistent_gnt *persistent_gnt)
{
struct rb_node **new = NULL, *parent = NULL;
struct persistent_gnt *this;
struct xen_blkif *blkif = ring->blkif;
if (ring->persistent_gnt_c >= xen_blkif_max_pgrants) {
if (!blkif->vbd.overflow_max_grants)
blkif->vbd.overflow_max_grants = 1;
return -EBUSY;
}
/* Figure out where to put new node */
new = &ring->persistent_gnts.rb_node;
while (*new) {
this = container_of(*new, struct persistent_gnt, node);
parent = *new;
if (persistent_gnt->gnt < this->gnt)
new = &((*new)->rb_left);
else if (persistent_gnt->gnt > this->gnt)
new = &((*new)->rb_right);
else {
pr_alert_ratelimited("trying to add a gref that's already in the tree\n");
return -EINVAL;
}
}
bitmap_zero(persistent_gnt->flags, PERSISTENT_GNT_FLAGS_SIZE);
set_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags);
/* Add new node and rebalance tree. */
rb_link_node(&(persistent_gnt->node), parent, new);
rb_insert_color(&(persistent_gnt->node), &ring->persistent_gnts);
ring->persistent_gnt_c++;
atomic_inc(&ring->persistent_gnt_in_use);
return 0;
}
static struct persistent_gnt *get_persistent_gnt(struct xen_blkif_ring *ring,
grant_ref_t gref)
{
struct persistent_gnt *data;
struct rb_node *node = NULL;
node = ring->persistent_gnts.rb_node;
while (node) {
data = container_of(node, struct persistent_gnt, node);
if (gref < data->gnt)
node = node->rb_left;
else if (gref > data->gnt)
node = node->rb_right;
else {
if(test_bit(PERSISTENT_GNT_ACTIVE, data->flags)) {
pr_alert_ratelimited("requesting a grant already in use\n");
return NULL;
}
set_bit(PERSISTENT_GNT_ACTIVE, data->flags);
atomic_inc(&ring->persistent_gnt_in_use);
return data;
}
}
return NULL;
}
static void put_persistent_gnt(struct xen_blkif_ring *ring,
struct persistent_gnt *persistent_gnt)
{
if(!test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags))
pr_alert_ratelimited("freeing a grant already unused\n");
set_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
clear_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags);
atomic_dec(&ring->persistent_gnt_in_use);
}
static void free_persistent_gnts(struct xen_blkif_ring *ring, struct rb_root *root,
unsigned int num)
{
struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct persistent_gnt *persistent_gnt;
struct rb_node *n;
int segs_to_unmap = 0;
struct gntab_unmap_queue_data unmap_data;
unmap_data.pages = pages;
unmap_data.unmap_ops = unmap;
unmap_data.kunmap_ops = NULL;
foreach_grant_safe(persistent_gnt, n, root, node) {
BUG_ON(persistent_gnt->handle ==
BLKBACK_INVALID_HANDLE);
gnttab_set_unmap_op(&unmap[segs_to_unmap],
(unsigned long) pfn_to_kaddr(page_to_pfn(
persistent_gnt->page)),
GNTMAP_host_map,
persistent_gnt->handle);
pages[segs_to_unmap] = persistent_gnt->page;
if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST ||
!rb_next(&persistent_gnt->node)) {
unmap_data.count = segs_to_unmap;
BUG_ON(gnttab_unmap_refs_sync(&unmap_data));
put_free_pages(ring, pages, segs_to_unmap);
segs_to_unmap = 0;
}
rb_erase(&persistent_gnt->node, root);
kfree(persistent_gnt);
num--;
}
BUG_ON(num != 0);
}
void xen_blkbk_unmap_purged_grants(struct work_struct *work)
{
struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct persistent_gnt *persistent_gnt;
int segs_to_unmap = 0;
struct xen_blkif_ring *ring = container_of(work, typeof(*ring), persistent_purge_work);
struct gntab_unmap_queue_data unmap_data;
unmap_data.pages = pages;
unmap_data.unmap_ops = unmap;
unmap_data.kunmap_ops = NULL;
while(!list_empty(&ring->persistent_purge_list)) {
persistent_gnt = list_first_entry(&ring->persistent_purge_list,
struct persistent_gnt,
remove_node);
list_del(&persistent_gnt->remove_node);
gnttab_set_unmap_op(&unmap[segs_to_unmap],
vaddr(persistent_gnt->page),
GNTMAP_host_map,
persistent_gnt->handle);
pages[segs_to_unmap] = persistent_gnt->page;
if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
unmap_data.count = segs_to_unmap;
BUG_ON(gnttab_unmap_refs_sync(&unmap_data));
put_free_pages(ring, pages, segs_to_unmap);
segs_to_unmap = 0;
}
kfree(persistent_gnt);
}
if (segs_to_unmap > 0) {
unmap_data.count = segs_to_unmap;
BUG_ON(gnttab_unmap_refs_sync(&unmap_data));
put_free_pages(ring, pages, segs_to_unmap);
}
}
static void purge_persistent_gnt(struct xen_blkif_ring *ring)
{
struct persistent_gnt *persistent_gnt;
struct rb_node *n;
unsigned int num_clean, total;
bool scan_used = false, clean_used = false;
struct rb_root *root;
if (ring->persistent_gnt_c < xen_blkif_max_pgrants ||
(ring->persistent_gnt_c == xen_blkif_max_pgrants &&
!ring->blkif->vbd.overflow_max_grants)) {
goto out;
}
if (work_busy(&ring->persistent_purge_work)) {
pr_alert_ratelimited("Scheduled work from previous purge is still busy, cannot purge list\n");
goto out;
}
num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN;
num_clean = ring->persistent_gnt_c - xen_blkif_max_pgrants + num_clean;
num_clean = min(ring->persistent_gnt_c, num_clean);
if ((num_clean == 0) ||
(num_clean > (ring->persistent_gnt_c - atomic_read(&ring->persistent_gnt_in_use))))
goto out;
/*
* At this point, we can assure that there will be no calls
* to get_persistent_grant (because we are executing this code from
* xen_blkif_schedule), there can only be calls to put_persistent_gnt,
* which means that the number of currently used grants will go down,
* but never up, so we will always be able to remove the requested
* number of grants.
*/
total = num_clean;
pr_debug("Going to purge %u persistent grants\n", num_clean);
BUG_ON(!list_empty(&ring->persistent_purge_list));
root = &ring->persistent_gnts;
purge_list:
foreach_grant_safe(persistent_gnt, n, root, node) {
BUG_ON(persistent_gnt->handle ==
BLKBACK_INVALID_HANDLE);
if (clean_used) {
clear_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
continue;
}
if (test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags))
continue;
if (!scan_used &&
(test_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags)))
continue;
rb_erase(&persistent_gnt->node, root);
list_add(&persistent_gnt->remove_node,
&ring->persistent_purge_list);
if (--num_clean == 0)
goto finished;
}
/*
* If we get here it means we also need to start cleaning
* grants that were used since last purge in order to cope
* with the requested num
*/
if (!scan_used && !clean_used) {
pr_debug("Still missing %u purged frames\n", num_clean);
scan_used = true;
goto purge_list;
}
finished:
if (!clean_used) {
pr_debug("Finished scanning for grants to clean, removing used flag\n");
clean_used = true;
goto purge_list;
}
ring->persistent_gnt_c -= (total - num_clean);
ring->blkif->vbd.overflow_max_grants = 0;
/* We can defer this work */
schedule_work(&ring->persistent_purge_work);
pr_debug("Purged %u/%u\n", (total - num_clean), total);
out:
return;
}
/*
* Retrieve from the 'pending_reqs' a free pending_req structure to be used.
*/
static struct pending_req *alloc_req(struct xen_blkif_ring *ring)
{
struct pending_req *req = NULL;
unsigned long flags;
spin_lock_irqsave(&ring->pending_free_lock, flags);
if (!list_empty(&ring->pending_free)) {
req = list_entry(ring->pending_free.next, struct pending_req,
free_list);
list_del(&req->free_list);
}
spin_unlock_irqrestore(&ring->pending_free_lock, flags);
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(struct xen_blkif_ring *ring, struct pending_req *req)
{
unsigned long flags;
int was_empty;
spin_lock_irqsave(&ring->pending_free_lock, flags);
was_empty = list_empty(&ring->pending_free);
list_add(&req->free_list, &ring->pending_free);
spin_unlock_irqrestore(&ring->pending_free_lock, flags);
if (was_empty)
wake_up(&ring->pending_free_wq);
}
/*
* Routines for managing virtual block devices (vbds).
*/
static int xen_vbd_translate(struct phys_req *req, struct xen_blkif *blkif,
int operation)
{
struct xen_vbd *vbd = &blkif->vbd;
int rc = -EACCES;
if ((operation != REQ_OP_READ) && vbd->readonly)
goto out;
if (likely(req->nr_sects)) {
blkif_sector_t end = req->sector_number + req->nr_sects;
if (unlikely(end < req->sector_number))
goto out;
if (unlikely(end > vbd_sz(vbd)))
goto out;
}
req->dev = vbd->pdevice;
req->bdev = vbd->bdev;
rc = 0;
out:
return rc;
}
static void xen_vbd_resize(struct xen_blkif *blkif)
{
struct xen_vbd *vbd = &blkif->vbd;
struct xenbus_transaction xbt;
int err;
struct xenbus_device *dev = xen_blkbk_xenbus(blkif->be);
unsigned long long new_size = vbd_sz(vbd);
pr_info("VBD Resize: Domid: %d, Device: (%d, %d)\n",
blkif->domid, MAJOR(vbd->pdevice), MINOR(vbd->pdevice));
pr_info("VBD Resize: new size %llu\n", new_size);
vbd->size = new_size;
again:
err = xenbus_transaction_start(&xbt);
if (err) {
pr_warn("Error starting transaction\n");
return;
}
err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
(unsigned long long)vbd_sz(vbd));
if (err) {
pr_warn("Error writing new size\n");
goto abort;
}
/*
* Write the current state; we will use this to synchronize
* the front-end. If the current state is "connected" the
* front-end will get the new size information online.
*/
err = xenbus_printf(xbt, dev->nodename, "state", "%d", dev->state);
if (err) {
pr_warn("Error writing the state\n");
goto abort;
}
err = xenbus_transaction_end(xbt, 0);
if (err == -EAGAIN)
goto again;
if (err)
pr_warn("Error ending transaction\n");
return;
abort:
xenbus_transaction_end(xbt, 1);
}
/*
* Notification from the guest OS.
*/
static void blkif_notify_work(struct xen_blkif_ring *ring)
{
ring->waiting_reqs = 1;
wake_up(&ring->wq);
}
irqreturn_t xen_blkif_be_int(int irq, void *dev_id)
{
blkif_notify_work(dev_id);
return IRQ_HANDLED;
}
/*
* SCHEDULER FUNCTIONS
*/
static void print_stats(struct xen_blkif_ring *ring)
{
pr_info("(%s): oo %3llu | rd %4llu | wr %4llu | f %4llu"
" | ds %4llu | pg: %4u/%4d\n",
current->comm, ring->st_oo_req,
ring->st_rd_req, ring->st_wr_req,
ring->st_f_req, ring->st_ds_req,
ring->persistent_gnt_c,
xen_blkif_max_pgrants);
ring->st_print = jiffies + msecs_to_jiffies(10 * 1000);
ring->st_rd_req = 0;
ring->st_wr_req = 0;
ring->st_oo_req = 0;
ring->st_ds_req = 0;
}
int xen_blkif_schedule(void *arg)
{
struct xen_blkif_ring *ring = arg;
struct xen_blkif *blkif = ring->blkif;
struct xen_vbd *vbd = &blkif->vbd;
unsigned long timeout;
int ret;
set_freezable();
while (!kthread_should_stop()) {
if (try_to_freeze())
continue;
if (unlikely(vbd->size != vbd_sz(vbd)))
xen_vbd_resize(blkif);
timeout = msecs_to_jiffies(LRU_INTERVAL);
timeout = wait_event_interruptible_timeout(
ring->wq,
ring->waiting_reqs || kthread_should_stop(),
timeout);
if (timeout == 0)
goto purge_gnt_list;
timeout = wait_event_interruptible_timeout(
ring->pending_free_wq,
!list_empty(&ring->pending_free) ||
kthread_should_stop(),
timeout);
if (timeout == 0)
goto purge_gnt_list;
ring->waiting_reqs = 0;
smp_mb(); /* clear flag *before* checking for work */
ret = do_block_io_op(ring);
if (ret > 0)
ring->waiting_reqs = 1;
if (ret == -EACCES)
wait_event_interruptible(ring->shutdown_wq,
kthread_should_stop());
purge_gnt_list:
if (blkif->vbd.feature_gnt_persistent &&
time_after(jiffies, ring->next_lru)) {
purge_persistent_gnt(ring);
ring->next_lru = jiffies + msecs_to_jiffies(LRU_INTERVAL);
}
/* Shrink if we have more than xen_blkif_max_buffer_pages */
shrink_free_pagepool(ring, xen_blkif_max_buffer_pages);
if (log_stats && time_after(jiffies, ring->st_print))
print_stats(ring);
}
/* Drain pending purge work */
flush_work(&ring->persistent_purge_work);
if (log_stats)
print_stats(ring);
ring->xenblkd = NULL;
return 0;
}
/*
* Remove persistent grants and empty the pool of free pages
*/
void xen_blkbk_free_caches(struct xen_blkif_ring *ring)
{
/* Free all persistent grant pages */
if (!RB_EMPTY_ROOT(&ring->persistent_gnts))
free_persistent_gnts(ring, &ring->persistent_gnts,
ring->persistent_gnt_c);
BUG_ON(!RB_EMPTY_ROOT(&ring->persistent_gnts));
ring->persistent_gnt_c = 0;
/* Since we are shutting down remove all pages from the buffer */
shrink_free_pagepool(ring, 0 /* All */);
}
static unsigned int xen_blkbk_unmap_prepare(
struct xen_blkif_ring *ring,
struct grant_page **pages,
unsigned int num,
struct gnttab_unmap_grant_ref *unmap_ops,
struct page **unmap_pages)
{
unsigned int i, invcount = 0;
for (i = 0; i < num; i++) {
if (pages[i]->persistent_gnt != NULL) {
put_persistent_gnt(ring, pages[i]->persistent_gnt);
continue;
}
if (pages[i]->handle == BLKBACK_INVALID_HANDLE)
continue;
unmap_pages[invcount] = pages[i]->page;
gnttab_set_unmap_op(&unmap_ops[invcount], vaddr(pages[i]->page),
GNTMAP_host_map, pages[i]->handle);
pages[i]->handle = BLKBACK_INVALID_HANDLE;
invcount++;
}
return invcount;
}
static void xen_blkbk_unmap_and_respond_callback(int result, struct gntab_unmap_queue_data *data)
{
struct pending_req *pending_req = (struct pending_req *)(data->data);
struct xen_blkif_ring *ring = pending_req->ring;
struct xen_blkif *blkif = ring->blkif;
/* BUG_ON used to reproduce existing behaviour,
but is this the best way to deal with this? */
BUG_ON(result);
put_free_pages(ring, data->pages, data->count);
make_response(ring, pending_req->id,
pending_req->operation, pending_req->status);
free_req(ring, pending_req);
/*
* Make sure the request is freed before releasing blkif,
* or there could be a race between free_req and the
* cleanup done in xen_blkif_free during shutdown.
*
* NB: The fact that we might try to wake up pending_free_wq
* before drain_complete (in case there's a drain going on)
* it's not a problem with our current implementation
* because we can assure there's no thread waiting on
* pending_free_wq if there's a drain going on, but it has
* to be taken into account if the current model is changed.
*/
if (atomic_dec_and_test(&ring->inflight) && atomic_read(&blkif->drain)) {
complete(&blkif->drain_complete);
}
xen_blkif_put(blkif);
}
static void xen_blkbk_unmap_and_respond(struct pending_req *req)
{
struct gntab_unmap_queue_data* work = &req->gnttab_unmap_data;
struct xen_blkif_ring *ring = req->ring;
struct grant_page **pages = req->segments;
unsigned int invcount;
invcount = xen_blkbk_unmap_prepare(ring, pages, req->nr_segs,
req->unmap, req->unmap_pages);
work->data = req;
work->done = xen_blkbk_unmap_and_respond_callback;
work->unmap_ops = req->unmap;
work->kunmap_ops = NULL;
work->pages = req->unmap_pages;
work->count = invcount;
gnttab_unmap_refs_async(&req->gnttab_unmap_data);
}
/*
* Unmap the grant references.
*
* This could accumulate ops up to the batch size to reduce the number
* of hypercalls, but since this is only used in error paths there's
* no real need.
*/
static void xen_blkbk_unmap(struct xen_blkif_ring *ring,
struct grant_page *pages[],
int num)
{
struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct page *unmap_pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
unsigned int invcount = 0;
int ret;
while (num) {
unsigned int batch = min(num, BLKIF_MAX_SEGMENTS_PER_REQUEST);
invcount = xen_blkbk_unmap_prepare(ring, pages, batch,
unmap, unmap_pages);
if (invcount) {
ret = gnttab_unmap_refs(unmap, NULL, unmap_pages, invcount);
BUG_ON(ret);
put_free_pages(ring, unmap_pages, invcount);
}
pages += batch;
num -= batch;
}
}
static int xen_blkbk_map(struct xen_blkif_ring *ring,
struct grant_page *pages[],
int num, bool ro)
{
struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct page *pages_to_gnt[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct persistent_gnt *persistent_gnt = NULL;
phys_addr_t addr = 0;
int i, seg_idx, new_map_idx;
int segs_to_map = 0;
int ret = 0;
int last_map = 0, map_until = 0;
int use_persistent_gnts;
struct xen_blkif *blkif = ring->blkif;
use_persistent_gnts = (blkif->vbd.feature_gnt_persistent);
/*
* 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.
*/
again:
for (i = map_until; i < num; i++) {
uint32_t flags;
if (use_persistent_gnts) {
persistent_gnt = get_persistent_gnt(
ring,
pages[i]->gref);
}
if (persistent_gnt) {
/*
* We are using persistent grants and
* the grant is already mapped
*/
pages[i]->page = persistent_gnt->page;
pages[i]->persistent_gnt = persistent_gnt;
} else {
if (get_free_page(ring, &pages[i]->page))
goto out_of_memory;
addr = vaddr(pages[i]->page);
pages_to_gnt[segs_to_map] = pages[i]->page;
pages[i]->persistent_gnt = NULL;
flags = GNTMAP_host_map;
if (!use_persistent_gnts && ro)
flags |= GNTMAP_readonly;
gnttab_set_map_op(&map[segs_to_map++], addr,
flags, pages[i]->gref,
blkif->domid);
}
map_until = i + 1;
if (segs_to_map == BLKIF_MAX_SEGMENTS_PER_REQUEST)
break;
}
if (segs_to_map) {
ret = gnttab_map_refs(map, NULL, pages_to_gnt, segs_to_map);
BUG_ON(ret);
}
/*
* Now swizzle 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 (seg_idx = last_map, new_map_idx = 0; seg_idx < map_until; seg_idx++) {
if (!pages[seg_idx]->persistent_gnt) {
/* This is a newly mapped grant */
BUG_ON(new_map_idx >= segs_to_map);
if (unlikely(map[new_map_idx].status != 0)) {
pr_debug("invalid buffer -- could not remap it\n");
put_free_pages(ring, &pages[seg_idx]->page, 1);
pages[seg_idx]->handle = BLKBACK_INVALID_HANDLE;
ret |= 1;
goto next;
}
pages[seg_idx]->handle = map[new_map_idx].handle;
} else {
continue;
}
if (use_persistent_gnts &&
ring->persistent_gnt_c < xen_blkif_max_pgrants) {
/*
* We are using persistent grants, the grant is
* not mapped but we might have room for it.
*/
persistent_gnt = kmalloc(sizeof(struct persistent_gnt),
GFP_KERNEL);
if (!persistent_gnt) {
/*
* If we don't have enough memory to
* allocate the persistent_gnt struct
* map this grant non-persistenly
*/
goto next;
}
persistent_gnt->gnt = map[new_map_idx].ref;
persistent_gnt->handle = map[new_map_idx].handle;
persistent_gnt->page = pages[seg_idx]->page;
if (add_persistent_gnt(ring,
persistent_gnt)) {
kfree(persistent_gnt);
persistent_gnt = NULL;
goto next;
}
pages[seg_idx]->persistent_gnt = persistent_gnt;
pr_debug("grant %u added to the tree of persistent grants, using %u/%u\n",
persistent_gnt->gnt, ring->persistent_gnt_c,
xen_blkif_max_pgrants);
goto next;
}
if (use_persistent_gnts && !blkif->vbd.overflow_max_grants) {
blkif->vbd.overflow_max_grants = 1;
pr_debug("domain %u, device %#x is using maximum number of persistent grants\n",
blkif->domid, blkif->vbd.handle);
}
/*
* We could not map this grant persistently, so use it as
* a non-persistent grant.
*/
next:
new_map_idx++;
}
segs_to_map = 0;
last_map = map_until;
if (map_until != num)
goto again;
return ret;
out_of_memory:
pr_alert("%s: out of memory\n", __func__);
put_free_pages(ring, pages_to_gnt, segs_to_map);
return -ENOMEM;
}
static int xen_blkbk_map_seg(struct pending_req *pending_req)
{
int rc;
rc = xen_blkbk_map(pending_req->ring, pending_req->segments,
pending_req->nr_segs,
(pending_req->operation != BLKIF_OP_READ));
return rc;
}
static int xen_blkbk_parse_indirect(struct blkif_request *req,
struct pending_req *pending_req,
struct seg_buf seg[],
struct phys_req *preq)
{
struct grant_page **pages = pending_req->indirect_pages;
struct xen_blkif_ring *ring = pending_req->ring;
int indirect_grefs, rc, n, nseg, i;
struct blkif_request_segment *segments = NULL;
nseg = pending_req->nr_segs;
indirect_grefs = INDIRECT_PAGES(nseg);
BUG_ON(indirect_grefs > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST);
for (i = 0; i < indirect_grefs; i++)
pages[i]->gref = req->u.indirect.indirect_grefs[i];
rc = xen_blkbk_map(ring, pages, indirect_grefs, true);
if (rc)
goto unmap;
for (n = 0, i = 0; n < nseg; n++) {
uint8_t first_sect, last_sect;
if ((n % SEGS_PER_INDIRECT_FRAME) == 0) {
/* Map indirect segments */
if (segments)
kunmap_atomic(segments);
segments = kmap_atomic(pages[n/SEGS_PER_INDIRECT_FRAME]->page);
}
i = n % SEGS_PER_INDIRECT_FRAME;
pending_req->segments[n]->gref = segments[i].gref;
first_sect = READ_ONCE(segments[i].first_sect);
last_sect = READ_ONCE(segments[i].last_sect);
if (last_sect >= (XEN_PAGE_SIZE >> 9) || last_sect < first_sect) {
rc = -EINVAL;
goto unmap;
}
seg[n].nsec = last_sect - first_sect + 1;
seg[n].offset = first_sect << 9;
preq->nr_sects += seg[n].nsec;
}
unmap:
if (segments)
kunmap_atomic(segments);
xen_blkbk_unmap(ring, pages, indirect_grefs);
return rc;
}
static int dispatch_discard_io(struct xen_blkif_ring *ring,
struct blkif_request *req)
{
int err = 0;
int status = BLKIF_RSP_OKAY;
struct xen_blkif *blkif = ring->blkif;
struct block_device *bdev = blkif->vbd.bdev;
unsigned long secure;
struct phys_req preq;
xen_blkif_get(blkif);
preq.sector_number = req->u.discard.sector_number;
preq.nr_sects = req->u.discard.nr_sectors;
err = xen_vbd_translate(&preq, blkif, REQ_OP_WRITE);
if (err) {
pr_warn("access denied: DISCARD [%llu->%llu] on dev=%04x\n",
preq.sector_number,
preq.sector_number + preq.nr_sects, blkif->vbd.pdevice);
goto fail_response;
}
ring->st_ds_req++;
secure = (blkif->vbd.discard_secure &&
(req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
BLKDEV_DISCARD_SECURE : 0;
err = blkdev_issue_discard(bdev, req->u.discard.sector_number,
req->u.discard.nr_sectors,
GFP_KERNEL, secure);
fail_response:
if (err == -EOPNOTSUPP) {
pr_debug("discard op failed, not supported\n");
status = BLKIF_RSP_EOPNOTSUPP;
} else if (err)
status = BLKIF_RSP_ERROR;
make_response(ring, req->u.discard.id, req->operation, status);
xen_blkif_put(blkif);
return err;
}
static int dispatch_other_io(struct xen_blkif_ring *ring,
struct blkif_request *req,
struct pending_req *pending_req)
{
free_req(ring, pending_req);
make_response(ring, req->u.other.id, req->operation,
BLKIF_RSP_EOPNOTSUPP);
return -EIO;
}
static void xen_blk_drain_io(struct xen_blkif_ring *ring)
{
struct xen_blkif *blkif = ring->blkif;
atomic_set(&blkif->drain, 1);
do {
if (atomic_read(&ring->inflight) == 0)
break;
wait_for_completion_interruptible_timeout(
&blkif->drain_complete, HZ);
if (!atomic_read(&blkif->drain))
break;
} while (!kthread_should_stop());
atomic_set(&blkif->drain, 0);
}
static void __end_block_io_op(struct pending_req *pending_req,
blk_status_t error)
{
/* An error fails the entire request. */
if (pending_req->operation == BLKIF_OP_FLUSH_DISKCACHE &&
error == BLK_STS_NOTSUPP) {
pr_debug("flush diskcache op failed, not supported\n");
xen_blkbk_flush_diskcache(XBT_NIL, pending_req->ring->blkif->be, 0);
pending_req->status = BLKIF_RSP_EOPNOTSUPP;
} else if (pending_req->operation == BLKIF_OP_WRITE_BARRIER &&
error == BLK_STS_NOTSUPP) {
pr_debug("write barrier op failed, not supported\n");
xen_blkbk_barrier(XBT_NIL, pending_req->ring->blkif->be, 0);
pending_req->status = BLKIF_RSP_EOPNOTSUPP;
} else if (error) {
pr_debug("Buffer not up-to-date at end of operation,"
" error=%d\n", 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))
xen_blkbk_unmap_and_respond(pending_req);
}
/*
* bio callback.
*/
static void end_block_io_op(struct bio *bio)
{
__end_block_io_op(bio->bi_private, bio->bi_status);
bio_put(bio);
}
/*
* 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(struct xen_blkif_ring *ring)
{
union blkif_back_rings *blk_rings = &ring->blk_rings;
struct blkif_request req;
struct pending_req *pending_req;
RING_IDX rc, rp;
int more_to_do = 0;
rc = blk_rings->common.req_cons;
rp = blk_rings->common.sring->req_prod;
rmb(); /* Ensure we see queued requests up to 'rp'. */
if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp)) {
rc = blk_rings->common.rsp_prod_pvt;
pr_warn("Frontend provided bogus ring requests (%d - %d = %d). Halting ring processing on dev=%04x\n",
rp, rc, rp - rc, ring->blkif->vbd.pdevice);
return -EACCES;
}
while (rc != rp) {
if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc))
break;
if (kthread_should_stop()) {
more_to_do = 1;
break;
}
pending_req = alloc_req(ring);
if (NULL == pending_req) {
ring->st_oo_req++;
more_to_do = 1;
break;
}
switch (ring->blkif->blk_protocol) {
case BLKIF_PROTOCOL_NATIVE:
memcpy(&req, RING_GET_REQUEST(&blk_rings->native, rc), sizeof(req));
break;
case BLKIF_PROTOCOL_X86_32:
blkif_get_x86_32_req(&req, RING_GET_REQUEST(&blk_rings->x86_32, rc));
break;
case BLKIF_PROTOCOL_X86_64:
blkif_get_x86_64_req(&req, RING_GET_REQUEST(&blk_rings->x86_64, rc));
break;
default:
BUG();
}
blk_rings->common.req_cons = ++rc; /* before make_response() */
/* Apply all sanity checks to /private copy/ of request. */
barrier();
switch (req.operation) {
case BLKIF_OP_READ:
case BLKIF_OP_WRITE:
case BLKIF_OP_WRITE_BARRIER:
case BLKIF_OP_FLUSH_DISKCACHE:
case BLKIF_OP_INDIRECT:
if (dispatch_rw_block_io(ring, &req, pending_req))
goto done;
break;
case BLKIF_OP_DISCARD:
free_req(ring, pending_req);
if (dispatch_discard_io(ring, &req))
goto done;
break;
default:
if (dispatch_other_io(ring, &req, pending_req))
goto done;
break;
}
/* Yield point for this unbounded loop. */
cond_resched();
}
done:
return more_to_do;
}
static int
do_block_io_op(struct xen_blkif_ring *ring)
{
union blkif_back_rings *blk_rings = &ring->blk_rings;
int more_to_do;
do {
more_to_do = __do_block_io_op(ring);
if (more_to_do)
break;
RING_FINAL_CHECK_FOR_REQUESTS(&blk_rings->common, more_to_do);
} while (more_to_do);
return more_to_do;
}
/*
* Transmutation of the 'struct blkif_request' to a proper 'struct bio'
* and call the 'submit_bio' to pass it to the underlying storage.
*/
static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
struct blkif_request *req,
struct pending_req *pending_req)
{
struct phys_req preq;
struct seg_buf *seg = pending_req->seg;
unsigned int nseg;
struct bio *bio = NULL;
struct bio **biolist = pending_req->biolist;
int i, nbio = 0;
int operation;
int operation_flags = 0;
struct blk_plug plug;
bool drain = false;
struct grant_page **pages = pending_req->segments;
unsigned short req_operation;
req_operation = req->operation == BLKIF_OP_INDIRECT ?
req->u.indirect.indirect_op : req->operation;
if ((req->operation == BLKIF_OP_INDIRECT) &&
(req_operation != BLKIF_OP_READ) &&
(req_operation != BLKIF_OP_WRITE)) {
pr_debug("Invalid indirect operation (%u)\n", req_operation);
goto fail_response;
}
switch (req_operation) {
case BLKIF_OP_READ:
ring->st_rd_req++;
operation = REQ_OP_READ;
break;
case BLKIF_OP_WRITE:
ring->st_wr_req++;
operation = REQ_OP_WRITE;
operation_flags = REQ_SYNC | REQ_IDLE;
break;
case BLKIF_OP_WRITE_BARRIER:
drain = true;
/* fall through */
case BLKIF_OP_FLUSH_DISKCACHE:
ring->st_f_req++;
operation = REQ_OP_WRITE;
operation_flags = REQ_PREFLUSH;
break;
default:
operation = 0; /* make gcc happy */
goto fail_response;
break;
}
/* Check that the number of segments is sane. */
nseg = req->operation == BLKIF_OP_INDIRECT ?
req->u.indirect.nr_segments : req->u.rw.nr_segments;
if (unlikely(nseg == 0 && operation_flags != REQ_PREFLUSH) ||
unlikely((req->operation != BLKIF_OP_INDIRECT) &&
(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) ||
unlikely((req->operation == BLKIF_OP_INDIRECT) &&
(nseg > MAX_INDIRECT_SEGMENTS))) {
pr_debug("Bad number of segments in request (%d)\n", nseg);
/* Haven't submitted any bio's yet. */
goto fail_response;
}
preq.nr_sects = 0;
pending_req->ring = ring;
pending_req->id = req->u.rw.id;
pending_req->operation = req_operation;
pending_req->status = BLKIF_RSP_OKAY;
pending_req->nr_segs = nseg;
if (req->operation != BLKIF_OP_INDIRECT) {
preq.dev = req->u.rw.handle;
preq.sector_number = req->u.rw.sector_number;
for (i = 0; i < nseg; i++) {
pages[i]->gref = req->u.rw.seg[i].gref;
seg[i].nsec = req->u.rw.seg[i].last_sect -
req->u.rw.seg[i].first_sect + 1;
seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
if ((req->u.rw.seg[i].last_sect >= (XEN_PAGE_SIZE >> 9)) ||
(req->u.rw.seg[i].last_sect <
req->u.rw.seg[i].first_sect))
goto fail_response;
preq.nr_sects += seg[i].nsec;
}
} else {
preq.dev = req->u.indirect.handle;
preq.sector_number = req->u.indirect.sector_number;
if (xen_blkbk_parse_indirect(req, pending_req, seg, &preq))
goto fail_response;
}
if (xen_vbd_translate(&preq, ring->blkif, operation) != 0) {
pr_debug("access denied: %s of [%llu,%llu] on dev=%04x\n",
operation == REQ_OP_READ ? "read" : "write",
preq.sector_number,
preq.sector_number + preq.nr_sects,
ring->blkif->vbd.pdevice);
goto fail_response;
}
/*
* This check _MUST_ be done after xen_vbd_translate as the preq.bdev
* is set there.
*/
for (i = 0; i < nseg; i++) {
if (((int)preq.sector_number|(int)seg[i].nsec) &
((bdev_logical_block_size(preq.bdev) >> 9) - 1)) {
pr_debug("Misaligned I/O request from domain %d\n",
ring->blkif->domid);
goto fail_response;
}
}
/* Wait on all outstanding I/O's and once that has been completed
* issue the flush.
*/
if (drain)
xen_blk_drain_io(pending_req->ring);
/*
* 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
* xen_blkbk_unmap.
*/
if (xen_blkbk_map_seg(pending_req))
goto fail_flush;
/*
* This corresponding xen_blkif_put is done in __end_block_io_op, or
* below (in "!bio") if we are handling a BLKIF_OP_DISCARD.
*/
xen_blkif_get(ring->blkif);
atomic_inc(&ring->inflight);
for (i = 0; i < nseg; i++) {
while ((bio == NULL) ||
(bio_add_page(bio,
pages[i]->page,
seg[i].nsec << 9,
seg[i].offset) == 0)) {
int nr_iovecs = min_t(int, (nseg-i), BIO_MAX_PAGES);
bio = bio_alloc(GFP_KERNEL, nr_iovecs);
if (unlikely(bio == NULL))
goto fail_put_bio;
biolist[nbio++] = bio;
bio_set_dev(bio, preq.bdev);
bio->bi_private = pending_req;
bio->bi_end_io = end_block_io_op;
bio->bi_iter.bi_sector = preq.sector_number;
bio_set_op_attrs(bio, operation, operation_flags);
}
preq.sector_number += seg[i].nsec;
}
/* This will be hit if the operation was a flush or discard. */
if (!bio) {
BUG_ON(operation_flags != REQ_PREFLUSH);
bio = bio_alloc(GFP_KERNEL, 0);
if (unlikely(bio == NULL))
goto fail_put_bio;
biolist[nbio++] = bio;
bio_set_dev(bio, preq.bdev);
bio->bi_private = pending_req;
bio->bi_end_io = end_block_io_op;
bio_set_op_attrs(bio, operation, operation_flags);
}
atomic_set(&pending_req->pendcnt, nbio);
blk_start_plug(&plug);
for (i = 0; i < nbio; i++)
submit_bio(biolist[i]);
/* Let the I/Os go.. */
blk_finish_plug(&plug);
if (operation == REQ_OP_READ)
ring->st_rd_sect += preq.nr_sects;
else if (operation == REQ_OP_WRITE)
ring->st_wr_sect += preq.nr_sects;
return 0;
fail_flush:
xen_blkbk_unmap(ring, pending_req->segments,
pending_req->nr_segs);
fail_response:
/* Haven't submitted any bio's yet. */
make_response(ring, req->u.rw.id, req_operation, BLKIF_RSP_ERROR);
free_req(ring, pending_req);
msleep(1); /* back off a bit */
return -EIO;
fail_put_bio:
for (i = 0; i < nbio; i++)
bio_put(biolist[i]);
atomic_set(&pending_req->pendcnt, 1);
__end_block_io_op(pending_req, BLK_STS_RESOURCE);
msleep(1); /* back off a bit */
return -EIO;
}
/*
* Put a response on the ring on how the operation fared.
*/
static void make_response(struct xen_blkif_ring *ring, u64 id,
unsigned short op, int st)
{
struct blkif_response *resp;
unsigned long flags;
union blkif_back_rings *blk_rings;
int notify;
spin_lock_irqsave(&ring->blk_ring_lock, flags);
blk_rings = &ring->blk_rings;
/* Place on the response ring for the relevant domain. */
switch (ring->blkif->blk_protocol) {
case BLKIF_PROTOCOL_NATIVE:
resp = RING_GET_RESPONSE(&blk_rings->native,
blk_rings->native.rsp_prod_pvt);
break;
case BLKIF_PROTOCOL_X86_32:
resp = RING_GET_RESPONSE(&blk_rings->x86_32,
blk_rings->x86_32.rsp_prod_pvt);
break;
case BLKIF_PROTOCOL_X86_64:
resp = RING_GET_RESPONSE(&blk_rings->x86_64,
blk_rings->x86_64.rsp_prod_pvt);
break;
default:
BUG();
}
resp->id = id;
resp->operation = op;
resp->status = st;
blk_rings->common.rsp_prod_pvt++;
RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
spin_unlock_irqrestore(&ring->blk_ring_lock, flags);
if (notify)
notify_remote_via_irq(ring->irq);
}
static int __init xen_blkif_init(void)
{
int rc = 0;
if (!xen_domain())
return -ENODEV;
if (xen_blkif_max_ring_order > XENBUS_MAX_RING_GRANT_ORDER) {
pr_info("Invalid max_ring_order (%d), will use default max: %d.\n",
xen_blkif_max_ring_order, XENBUS_MAX_RING_GRANT_ORDER);
xen_blkif_max_ring_order = XENBUS_MAX_RING_GRANT_ORDER;
}
if (xenblk_max_queues == 0)
xenblk_max_queues = num_online_cpus();
rc = xen_blkif_interface_init();
if (rc)
goto failed_init;
rc = xen_blkif_xenbus_init();
if (rc)
goto failed_init;
failed_init:
return rc;
}
module_init(xen_blkif_init);
MODULE_LICENSE("Dual BSD/GPL");
MODULE_ALIAS("xen-backend:vbd");