On 10.11.2019 22:08, Denis Plotnikov wrote:
>
> On 10.11.2019 22:03, Denis Plotnikov wrote:
>> This allows to change (replace) the file on a block device and is useful
>> to workaround exclusive file access restrictions, e.g. to implement VM
>> migration with a shared disk stored on some storage with the exclusive
>> file opening model: a destination VM is started waiting for incomming
>> migration with a fake image drive, and later, on the last migration
>> phase, the fake image file is replaced with the real one.
>>
>> Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com>
>> ---
>> hw/core/qdev-properties-system.c | 89 +++++++++++++++++++++++++++-----
>> 1 file changed, 77 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/core/qdev-properties-system.c
>> b/hw/core/qdev-properties-system.c
>> index c534590dcd..aaab1370a4 100644
>> --- a/hw/core/qdev-properties-system.c
>> +++ b/hw/core/qdev-properties-system.c
>> @@ -79,8 +79,55 @@ static void set_pointer(Object *obj, Visitor *v,
>> Property *prop,
>> /* --- drive --- */
>> -static void do_parse_drive(DeviceState *dev, const char *str, void
>> **ptr,
>> - const char *propname, bool iothread,
>> Error **errp)
>> +static void do_parse_drive_realized(DeviceState *dev, const char *str,
>> + void **ptr, const char *propname,
>> + bool iothread, Error **errp)
>> +{
>> + BlockBackend *blk = *ptr;
>> + BlockDriverState *bs = bdrv_lookup_bs(NULL, str, NULL);
>> + int ret;
>> + bool blk_created = false;
>> +
>> + if (!bs) {
>> + error_setg(errp, "Can't find blockdev '%s'", str);
>> + return;
>> + }
>> +
>> + if (!blk) {
>> + AioContext *ctx = iothread ? bdrv_get_aio_context(bs) :
>> + qemu_get_aio_context();
>> + blk = blk_new(ctx, BLK_PERM_ALL, BLK_PERM_ALL);
>> + blk_created = true;
>
> Actually, I have concerns about situation where blk=null.
>
> Is there any case when scsi-hd (or others) doesn't have a blk assigned
> and it's legal?
>
>> + } else {
>> + if (blk_bs(blk)) {
>> + blk_remove_bs(blk);
>> + }
>> + }
>> +
>> + ret = blk_insert_bs(blk, bs, errp);
>> +
>> + if (!ret && blk_created) {
>> + if (blk_attach_dev(blk, dev) < 0) {
>> + /*
>> + * Shouldn't be any errors here since we just created
>> + * the new blk because the device doesn't have any.
>> + * Leave the message here in case blk_attach_dev is changed
>> + */
>> + error_setg(errp, "Can't attach drive '%s' to device '%s'",
>> + str, object_get_typename(OBJECT(dev)));
>> + } else {
>> + *ptr = blk;
>> + }
>> + }
Another problem here, is that the "size" of the device dev may not match
after setting a drive.
So, we should update it after the drive setting.
It was found, that it could be done by calling
BlockDevOps.bdrv_parent_cb_resize.
But I have some concerns about doing it so. In the case of virtio scsi
disk we have the following callstack
bdrv_parent_cb_resize calls() ->
scsi_device_report_change(dev, SENSE_CODE(CAPACITY_CHANGED)) ->
virtio_scsi_change ->
virtio_scsi_push_event(s, dev, VIRTIO_SCSI_T_PARAM_CHANGE,
sense.asc |
(sense.ascq << 8));
virtio_scsi_change pushes the event to the guest to make the guest ask
for size refreshing.
If I'm not mistaken, here we can get a race condition when some another
request is processed with an unchanged
size and then the size changing request is processed.
I didn't find a better way to update device size so any comments are
welcome.
Thanks!
Denis
>> +
>> + if (blk_created) {
>> + blk_unref(blk);
>> + }
>> +}
>> +
>> +static void do_parse_drive_unrealized(DeviceState *dev, const char
>> *str,
>> + void **ptr, const char *propname,
>> + bool iothread, Error **errp)
>> {
>> BlockBackend *blk;
>> bool blk_created = false;
>> @@ -137,18 +184,34 @@ fail:
>> }
>> }
>> -static void parse_drive(DeviceState *dev, const char *str, void
>> **ptr,
>> - const char *propname, Error **errp)
>> -{
>> - do_parse_drive(dev, str, ptr, propname, false, errp);
>> -}
>> -
>> -static void parse_drive_iothread(DeviceState *dev, const char *str,
>> void **ptr,
>> +static void parse_drive_realized(DeviceState *dev, const char *str,
>> void **ptr,
>> const char *propname, Error **errp)
>> {
>> - do_parse_drive(dev, str, ptr, propname, true, errp);
>> + do_parse_drive_realized(dev, str, ptr, propname, false, errp);
>> }
>> +static void parse_drive_realized_iothread(DeviceState *dev, const
>> char *str,
>> + void **ptr, const char
>> *propname,
>> + Error **errp)
>> +{
>> + do_parse_drive_realized(dev, str, ptr, propname, true, errp);
>> +}
>> +
>> +static void parse_drive_unrealized(DeviceState *dev, const char *str,
>> + void **ptr, const char *propname,
>> + Error **errp)
>> +{
>> + do_parse_drive_unrealized(dev, str, ptr, propname, false, errp);
>> +}
>> +
>> +static void parse_drive_unrealized_iothread(DeviceState *dev, const
>> char *str,
>> + void **ptr, const char
>> *propname,
>> + Error **errp)
>> +{
>> + do_parse_drive_unrealized(dev, str, ptr, propname, true, errp);
>> +}
>> +
>> +
>> static void release_drive(Object *obj, const char *name, void *opaque)
>> {
>> DeviceState *dev = DEVICE(obj);
>> @@ -188,13 +251,15 @@ static void get_drive(Object *obj, Visitor *v,
>> const char *name, void *opaque,
>> static void set_drive(Object *obj, Visitor *v, const char *name,
>> void *opaque,
>> Error **errp)
>> {
>> - set_pointer(obj, v, opaque, NULL, parse_drive, name, errp);
>> + set_pointer(obj, v, opaque, parse_drive_realized,
>> parse_drive_unrealized,
>> + name, errp);
>> }
>> static void set_drive_iothread(Object *obj, Visitor *v, const
>> char *name,
>> void *opaque, Error **errp)
>> {
>> - set_pointer(obj, v, opaque, NULL, parse_drive_iothread, name,
>> errp);
>> + set_pointer(obj, v, opaque, parse_drive_realized_iothread,
>> + parse_drive_unrealized_iothread, name, errp);
>> }
>> const PropertyInfo qdev_prop_drive = {
