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;
> + }
> + }
> +
> + 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 = {
