Kevin Wolf <[email protected]> writes: > The error handling policy was traditionally set with -drive, but with > -blockdev it is no longer possible to set frontend options. scsi-disk > (and other block devices) have long supported qdev properties to > configure the error handling policy, so let's add these options to > usb-storage as well and just forward them to the internal scsi-disk > instance. > > Signed-off-by: Kevin Wolf <[email protected]>
Let's see whether I remember / figure out how this stuff works. Not all devices support error handling policy, but scsi-disk does. The preferred way to configure error handling policy is with qdev properties rerror, werror. blkconf_apply_backend_options() propagates them to the associated BlockBackend. The outmoded way is with -drive parameters rerror, werror. blockdev_init() propagates them to the BlockBackend. If you use both ways, qdev properties win. usb-storage is a hack: it tries to look like a block device, but it's really a SCSI controller that can serve only a single scsi-disk device, which it creates automatically. We want to deprecate -drive. We also want to deprecate usb-storage, but I guess we're still not ready for that (it's a complicated story). To deprecate -drive without also deprecating usb-storage, we need to preserve features. The outmoded way works with usb-storage: the automatically created scsi-disk is associated with the BlockBackend that got its error handling policy from -drive. The preferred way doesn't, because usb-storage lacks the qdev properties. This patch adds them. Kind of sad, but it's either that or deprecating usb-storage. Patch looks good to me, thus Reviewed-by: Markus Armbruster <[email protected]> Feel free to work whatever parts of my ramblings you find useful into your commit message.
