The 10/22/2020 08:58, Hannes Reinecke wrote: > On 10/21/20 4:10 PM, Sergei Shtepa wrote: > > The 10/21/2020 16:31, Hannes Reinecke wrote: > >> I do understand where you are coming from, but then we already have a > >> dm-snap which does exactly what you want to achieve. > >> Of course, that would require a reconfiguration of the storage stack on > >> the machine, which is not always possible (or desired). > > > > Yes, reconfiguring the storage stack on a machine is almost impossible. > > > >> > >> What I _could_ imagine would be a 'dm-intercept' thingie, which > >> redirects the current submit_bio() function for any block device, and > >> re-routes that to a linear device-mapper device pointing back to the > >> original block device. > >> > >> That way you could attach it to basically any block device, _and_ can > >> use the existing device-mapper functionality to do fancy stuff once the > >> submit_io() callback has been re-routed. > >> > >> And it also would help in other scenarios, too; with such a > >> functionality we could seamlessly clone devices without having to move > >> the whole setup to device-mapper first. > > > > Hm... > > Did I understand correctly that the filter itself can be left approximately > > as it is, but the blk-snap module can be replaced with 'dm-intercept', > > which would use the re-route mechanism from the dm? > > I think I may be able to implement it, if you describe your idea in more > > detail. > > > > > Actually, once we have an dm-intercept, why do you need the block-layer > filter at all? > From you initial description the block-layer filter was implemented > such that blk-snap could work; but if we have dm-intercept (and with it > the ability to use device-mapper functionality even for normal block > devices) there wouldn't be any need for the block-layer filter, no? Maybe, but the problem is that I can't imagine how to implement dm-intercept yet. How to use dm to implement interception without changing the stack of block devices. We'll have to make a hook somewhere, isn`t it? > > Cheers, > > Hannes > -- > Dr. Hannes Reinecke Kernel Storage Architect > hare@xxxxxxx +49 911 74053 688 > SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg > HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer -- Sergei Shtepa Veeam Software developer.
