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[Xen-devel] [PATCH 3/3] xen-blkback: refactor vbd remove/disconnect.

To: Daniel Stodden <daniel.stodden@xxxxxxxxxx>, Jens Axboe <jaxboe@xxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Annie Li <annie.li@xxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Kurt C Hackel <KURT.HACKEL@xxxxxxxxxx>
Subject: [Xen-devel] [PATCH 3/3] xen-blkback: refactor vbd remove/disconnect.
From: Joe Jin <joe.jin@xxxxxxxxxx>
Date: Wed, 03 Aug 2011 10:14:29 +0800
Cc: Greg Marsden <greg.marsden@xxxxxxxxxx>, Joe Jin <joe.jin@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>
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This patch refactor vbd remove/disconnect.
1. Add blkback shutdown watch for the remove/disconnect.
2. Don't disconnect backend when frontend state is XenbusStateClosing
   until frontend state changed to XenbusStateClosed.

Signed-off-by: Joe Jin <joe.jin@xxxxxxxxxx>
Cc: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Cc: Jens Axboe <jaxboe@xxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Annie Li <annie.li@xxxxxxxxxx>
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
---
 drivers/block/xen-blkback/xenbus.c |  202 
++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 181 insertions(+), 21 deletions(-)

diff --git a/drivers/block/xen-blkback/xenbus.c 
b/drivers/block/xen-blkback/xenbus.c
index 3f129b4..2bb9727 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -25,16 +25,25 @@ struct backend_info {
        struct xenbus_device    *dev;
        struct xen_blkif        *blkif;
        struct xenbus_watch     backend_watch;
+       struct xenbus_watch     shutdown_watch;
        unsigned                major;
        unsigned                minor;
        char                    *mode;
+       int                     group_added;
+       char                    *nodename;
+       atomic_t                refcnt;
+       pid_t                   kthread_pid;
+       int                     shutdown_signalled;
 };
 
+DEFINE_SEMAPHORE(blkback_dev_sem);
+
 static struct kmem_cache *xen_blkif_cachep;
 static void connect(struct backend_info *);
 static int connect_ring(struct backend_info *);
 static void backend_changed(struct xenbus_watch *, const char **,
                            unsigned int);
+static void xen_vbd_free(struct xen_vbd *vbd);
 
 struct xenbus_device *xen_blkbk_xenbus(struct backend_info *be)
 {
@@ -99,6 +108,16 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
                blkif->xenblkd = NULL;
                xenbus_dev_error(blkif->be->dev, err, "start xenblkd");
        }
+       
+       blkif->be->kthread_pid = blkif->xenblkd->pid;
+       atomic_inc(&blkif->be->refcnt);
+
+       err = xenbus_printf(XBT_NIL, blkif->be->dev->nodename, "kthread-pid",
+                           "%d", blkif->xenblkd->pid);
+       if (err) {
+               xenbus_dev_error(blkif->be->dev, err, "write kthread-pid");
+               return;
+       }
 }
 
 static struct xen_blkif *xen_blkif_alloc(domid_t domid)
@@ -213,11 +232,6 @@ static int xen_blkif_map(struct xen_blkif *blkif, unsigned 
long shared_page,
 
 static void xen_blkif_disconnect(struct xen_blkif *blkif)
 {
-       if (blkif->xenblkd) {
-               kthread_stop(blkif->xenblkd);
-               blkif->xenblkd = NULL;
-       }
-
        atomic_dec(&blkif->refcnt);
        wait_event(blkif->waiting_to_free, atomic_read(&blkif->refcnt) == 0);
        atomic_inc(&blkif->refcnt);
@@ -296,6 +310,7 @@ VBD_SHOW(mode, "%s\n", be->mode);
 int xenvbd_sysfs_addif(struct xenbus_device *dev)
 {
        int error;
+       struct backend_info *be = dev_get_drvdata(&dev->dev);
 
        error = device_create_file(&dev->dev, &dev_attr_physical_device);
        if (error)
@@ -309,6 +324,8 @@ int xenvbd_sysfs_addif(struct xenbus_device *dev)
        if (error)
                goto fail3;
 
+       be->group_added = 1;
+
        return 0;
 
 fail3: sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
@@ -319,11 +336,73 @@ fail1:    device_remove_file(&dev->dev, 
&dev_attr_physical_device);
 
 void xenvbd_sysfs_delif(struct xenbus_device *dev)
 {
+       struct backend_info *be = dev_get_drvdata(&dev->dev);
+       if (be->group_added == 0)
+               return;
        sysfs_remove_group(&dev->dev.kobj, &xen_vbdstat_group);
        device_remove_file(&dev->dev, &dev_attr_mode);
        device_remove_file(&dev->dev, &dev_attr_physical_device);
+       be->group_added = 0;
+}
+
+static int xenvbd_kthread_remove(struct backend_info *be)
+{
+       struct xen_blkif *blkif = be->blkif;
+
+       if (!blkif || !blkif->xenblkd)
+               return 0;
+
+       blkif->remove_requested = 1;
+       wake_up_process(blkif->xenblkd);
+
+       return -EBUSY;
+}
+
+static void xenvbd_signal_shutdown(struct backend_info *be)
+{
+       int err;
+
+       down(&blkback_dev_sem);
+
+       if (be->shutdown_signalled)
+               goto out;
+
+       err = xenbus_write(XBT_NIL, be->nodename, "shutdown-done", "");
+       if (err)
+               WPRINTK("Error writing shutdown-done for %s: %d\n", 
+                       be->nodename, err);
+
+       if (be->dev)
+               xenbus_switch_state(be->dev, XenbusStateClosed);
+
+       be->shutdown_signalled = 1;
+
+ out:
+       up(&blkback_dev_sem);
 }
 
+static void backend_release(struct backend_info *be)
+{
+       struct xen_blkif *blkif = be->blkif;
+
+       if (current->pid == be->kthread_pid)
+               xenvbd_signal_shutdown(be);
+
+       if (!atomic_dec_and_test(&be->refcnt))
+               return;
+
+       xenvbd_signal_shutdown(be);
+
+       if (blkif) {
+               xen_blkif_disconnect(blkif);
+               xen_vbd_free(&blkif->vbd);
+               xen_blkif_free(blkif);
+               be->blkif = NULL;
+       }
+
+       kfree(be->nodename);
+       kfree(be);
+ }
 
 static void xen_vbd_free(struct xen_vbd *vbd)
 {
@@ -332,6 +411,12 @@ static void xen_vbd_free(struct xen_vbd *vbd)
        vbd->bdev = NULL;
 }
 
+void xen_vbd_sync(struct xen_vbd *vbd)
+{
+       if (vbd->bdev)
+               fsync_bdev(vbd->bdev);
+}
+
 static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
                          unsigned major, unsigned minor, int readonly,
                          int cdrom)
@@ -384,8 +469,9 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
 
        DPRINTK("");
 
-       if (be->major || be->minor)
-               xenvbd_sysfs_delif(dev);
+       down(&blkback_dev_sem);
+       be->dev = NULL;
+       up(&blkback_dev_sem);
 
        if (be->backend_watch.node) {
                unregister_xenbus_watch(&be->backend_watch);
@@ -393,18 +479,73 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
                be->backend_watch.node = NULL;
        }
 
-       if (be->blkif) {
-               xen_blkif_disconnect(be->blkif);
-               xen_vbd_free(&be->blkif->vbd);
-               xen_blkif_free(be->blkif);
-               be->blkif = NULL;
+       if (be->shutdown_watch.node) {
+               unregister_xenbus_watch(&be->shutdown_watch);
+               kfree(be->shutdown_watch.node);
+               be->shutdown_watch.node = NULL;
        }
 
-       kfree(be);
+       if (xenvbd_kthread_remove(be))
+               WPRINTK("BAD REMOVE REQUEST for %s\n", be->nodename);
+
+       xenvbd_sysfs_delif(dev);
+       backend_release(be);
+
        dev_set_drvdata(&dev->dev, NULL);
+
        return 0;
 }
 
+/*
+ * called by kthread when closing
+ */
+void xen_blkback_close(struct xen_blkif *blkif)
+{
+       xen_blkif_disconnect(blkif);
+       xen_vbd_sync(&blkif->vbd);
+       blkif->remove_requested = 0;
+
+       down(&blkback_dev_sem);
+       if (blkif->be->dev)
+               xenvbd_sysfs_delif(blkif->be->dev);
+       up(&blkback_dev_sem);
+
+       backend_release(blkif->be);
+       blkif->xenblkd = NULL;
+}
+
+static void xenvbd_start_shutdown(struct xenbus_watch *watch,
+                          const char **vec, unsigned int length)
+{
+       int err;
+       char *type;
+       unsigned int len;
+       struct backend_info *be
+               = container_of(watch, struct backend_info, shutdown_watch);
+       struct xenbus_device *dev = be->dev;
+
+       if (be->shutdown_signalled)
+               return;
+
+       type = xenbus_read(XBT_NIL, dev->nodename, "shutdown-request", &len);
+       err  = (IS_ERR(type) ? PTR_ERR(type) : 0);
+
+       if (XENBUS_EXIST_ERR(err))
+               return;
+
+       if (err) {
+               xenbus_dev_fatal(dev, err, "reading shutdown-request");
+               return;
+       }
+
+       xenbus_switch_state(dev, XenbusStateClosing);
+       
+       if (len == sizeof("force") - 1 && !memcmp(type, "force", len))
+               if (!xenvbd_kthread_remove(be))
+                       xenvbd_signal_shutdown(be); /* shutdown immediately */
+
+       kfree(type);
+ }
 int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
                              struct backend_info *be, int state)
 {
@@ -437,6 +578,15 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
        }
        be->dev = dev;
        dev_set_drvdata(&dev->dev, be);
+       atomic_set(&be->refcnt, 1);
+
+       be->nodename = kasprintf(GFP_KERNEL, "%s", dev->nodename);
+       if (!be->nodename) {
+               xenbus_dev_fatal(dev, -ENOMEM,
+                                "allocating backend structure");
+               kfree(be);
+               return -ENOMEM;
+       }
 
        be->blkif = xen_blkif_alloc(dev->otherend_id);
        if (IS_ERR(be->blkif)) {
@@ -454,6 +604,11 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
        if (err)
                goto fail;
 
+       err = xenbus_watch_pathfmt(dev, &be->shutdown_watch, 
xenvbd_start_shutdown,
+                                  "%s/%s", dev->nodename, "shutdown-request");
+       if (err)
+               goto fail;
+
        err = xenbus_switch_state(dev, XenbusStateInitWait);
        if (err)
                goto fail;
@@ -567,13 +722,17 @@ static void frontend_changed(struct xenbus_device *dev,
        struct backend_info *be = dev_get_drvdata(&dev->dev);
        int err;
 
-       DPRINTK("%s", xenbus_strstate(frontend_state));
+       DPRINTK("%s: %s", dev->nodename, xenbus_strstate(frontend_state));
 
        switch (frontend_state) {
        case XenbusStateInitialising:
                if (dev->state == XenbusStateClosed) {
                        pr_info(DRV_PFX "%s: prepare for reconnect\n",
                                dev->nodename);
+
+                       xenbus_rm(XBT_NIL, dev->nodename, "shutdown-done");
+                       be->shutdown_signalled = 0;
+
                        xenbus_switch_state(dev, XenbusStateInitWait);
                }
                break;
@@ -590,7 +749,7 @@ static void frontend_changed(struct xenbus_device *dev,
 
                /*
                 * Enforce precondition before potential leak point.
-                * blkif_disconnect() is idempotent.
+                * xen_blkif_disconnect() is idempotent.
                 */
                xen_blkif_disconnect(be->blkif);
 
@@ -601,17 +760,16 @@ static void frontend_changed(struct xenbus_device *dev,
                break;
 
        case XenbusStateClosing:
-               xen_blkif_disconnect(be->blkif);
                xenbus_switch_state(dev, XenbusStateClosing);
                break;
 
        case XenbusStateClosed:
-               xenbus_switch_state(dev, XenbusStateClosed);
-               if (xenbus_dev_is_online(dev))
-                       break;
-               /* fall through if not online */
+               if (!xenvbd_kthread_remove(be))
+                       xenvbd_signal_shutdown(be);
+               break;
+
        case XenbusStateUnknown:
-               /* implies blkif_disconnect() via blkback_remove() */
+               /* implies xen_blkif_disconnect() via blkback_remove() */
                device_unregister(&dev->dev);
                break;
 
@@ -620,6 +778,8 @@ static void frontend_changed(struct xenbus_device *dev,
                                 frontend_state);
                break;
        }
+
+       DPRINTK("%s: %s", dev->nodename, xenbus_strstate(dev->state));
 }
 
 



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