[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[PING]Re: [PATCH v0 2/2] block: allow to set 'drive' property on a reali
From: |
Denis Plotnikov |
Subject: |
[PING]Re: [PATCH v0 2/2] block: allow to set 'drive' property on a realized block device |
Date: |
Fri, 13 Dec 2019 07:30:38 +0000 |
On 18.11.2019 13:50, Denis Plotnikov wrote:
>
>
> 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 <address@hidden>
>>> ---
>>> 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 = {
>
[Prev in Thread] |
Current Thread |
[Next in Thread] |
- [PING]Re: [PATCH v0 2/2] block: allow to set 'drive' property on a realized block device,
Denis Plotnikov <=