Hi List, As you all know, I'm working on a userspace-controlled CoW implementation using device-mapper. The idea is to offer a pseudo device through device-mapper that has CoW behavior, but where the block allocation decisions are made from userspace. My thoughts are that it might be best to abandon the concept of the "dm-cow" target and instead work on a "dm-userspace" target. The userspace cow application I'm working on would remain mostly the same. Similarly, dm-userspace would look almost identical to my dm-cow does right now, but more generic. The target would simply present the details of the data passed to the map() function to userspace, which would respond with a target device and sector of where to send the request. A generic dm-userspace target would allow for testing of new algorithms (RAID, CoW, etc) from a userspace application, as well as some more interesting things involving distributed applications. Just like FUSE allows for some neat (although not necessarily high-performance) tricks, dm-userspace could allow the same thing for block devices. Would the device-mapper maintainers be interested in accepting something like dm-userspace upstream? -- Dan Smith IBM Linux Technology Center Open Hypervisor Team email: danms@xxxxxxxxxx
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