[Xen-devel] [PATCH v3] xen-block: handle resize callback

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

Some frontend drivers will handle dynamic resizing of PV disks, so set up
the BlockDevOps resize_cb() method during xen_block_realize() to allow
this to be done.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
Cc: Kevin Wolf <kwolf@xxxxxxxxxx>
Cc: Max Reitz <mreitz@xxxxxxxxxx>

v3:
 - really re-write the backend state by directly calling
   xen_device_backend_printf() directly
 - tested against a Debian Jessie guest as well as Windows 10

v2:
 - re-write backend state after updating sectors
---
 hw/block/dataplane/xen-block.c |  4 +---
 hw/block/trace-events          |  1 +
 hw/block/xen-block.c           | 40 ++++++++++++++++++++++++++++++----
 3 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c
index d0d8905a33..c6a15da024 100644
--- a/hw/block/dataplane/xen-block.c
+++ b/hw/block/dataplane/xen-block.c
@@ -50,7 +50,6 @@ struct XenBlockDataPlane {
     unsigned int nr_ring_ref;
     void *sring;
     int64_t file_blk;
-    int64_t file_size;
     int protocol;
     blkif_back_rings_t rings;
     int more_work;
@@ -189,7 +188,7 @@ static int xen_block_parse_request(XenBlockRequest *request)
                request->req.seg[i].first_sect + 1) * dataplane->file_blk;
         request->size += len;
     }
-    if (request->start + request->size > dataplane->file_size) {
+    if (request->start + request->size > blk_getlength(dataplane->blk)) {
         error_report("error: access beyond end of file");
         goto err;
     }
@@ -638,7 +637,6 @@ XenBlockDataPlane *xen_block_dataplane_create(XenDevice 
*xendev,
     dataplane->xendev = xendev;
     dataplane->file_blk = conf->logical_block_size;
     dataplane->blk = conf->blk;
-    dataplane->file_size = blk_getlength(dataplane->blk);
 
     QLIST_INIT(&dataplane->inflight);
     QLIST_INIT(&dataplane->freelist);
diff --git a/hw/block/trace-events b/hw/block/trace-events
index d0851953c5..8020f9226a 100644
--- a/hw/block/trace-events
+++ b/hw/block/trace-events
@@ -126,6 +126,7 @@ xen_block_realize(const char *type, uint32_t disk, uint32_t 
partition) "%s d%up%
 xen_block_connect(const char *type, uint32_t disk, uint32_t partition) "%s 
d%up%u"
 xen_block_disconnect(const char *type, uint32_t disk, uint32_t partition) "%s 
d%up%u"
 xen_block_unrealize(const char *type, uint32_t disk, uint32_t partition) "%s 
d%up%u"
+xen_block_size(const char *type, uint32_t disk, uint32_t partition, int64_t 
sectors) "%s d%up%u %"PRIi64
 xen_disk_realize(void) ""
 xen_disk_unrealize(void) ""
 xen_cdrom_realize(void) ""
diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index a636487b3e..5012af9cb6 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -144,6 +144,38 @@ static void xen_block_unrealize(XenDevice *xendev, Error 
**errp)
     }
 }
 
+static void xen_block_set_size(XenBlockDevice *blockdev)
+{
+    const char *type = object_get_typename(OBJECT(blockdev));
+    XenBlockVdev *vdev = &blockdev->props.vdev;
+    BlockConf *conf = &blockdev->props.conf;
+    int64_t sectors = blk_getlength(conf->blk) / conf->logical_block_size;
+    XenDevice *xendev = XEN_DEVICE(blockdev);
+
+    trace_xen_block_size(type, vdev->disk, vdev->partition, sectors);
+
+    xen_device_backend_printf(xendev, "sectors", "%"PRIi64, sectors);
+}
+
+static void xen_block_resize_cb(void *opaque)
+{
+    XenBlockDevice *blockdev = opaque;
+    XenDevice *xendev = XEN_DEVICE(blockdev);
+    enum xenbus_state state = xen_device_backend_get_state(xendev);
+
+    xen_block_set_size(blockdev);
+
+    /*
+     * Mimic the behaviour of Linux xen-blkback and re-write the state
+     * to trigger the frontend watch.
+     */
+    xen_device_backend_printf(xendev, "state", "%u", state);
+}
+
+static const BlockDevOps xen_block_dev_ops = {
+    .resize_cb = xen_block_resize_cb,
+};
+
 static void xen_block_realize(XenDevice *xendev, Error **errp)
 {
     XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev);
@@ -180,7 +212,7 @@ static void xen_block_realize(XenDevice *xendev, Error 
**errp)
     }
 
     if (!blkconf_apply_backend_options(conf, blockdev->info & VDISK_READONLY,
-                                       false, errp)) {
+                                       true, errp)) {
         return;
     }
 
@@ -197,6 +229,7 @@ static void xen_block_realize(XenDevice *xendev, Error 
**errp)
         return;
     }
 
+    blk_set_dev_ops(conf->blk, &xen_block_dev_ops, blockdev);
     blk_set_guest_block_size(conf->blk, conf->logical_block_size);
 
     if (conf->discard_granularity > 0) {
@@ -215,9 +248,8 @@ static void xen_block_realize(XenDevice *xendev, Error 
**errp)
 
     xen_device_backend_printf(xendev, "sector-size", "%u",
                               conf->logical_block_size);
-    xen_device_backend_printf(xendev, "sectors", "%"PRIi64,
-                              blk_getlength(conf->blk) /
-                              conf->logical_block_size);
+
+    xen_block_set_size(blockdev);
 
     blockdev->dataplane =
         xen_block_dataplane_create(xendev, conf, blockdev->props.iothread);
-- 
2.20.1.2.gb21ebb6


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