disk_backend: add new layered disk #404
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Add a new disk type `LayeredDisk` that is composed of multiple layers, each of which can contribute an arbitrary subset of the sectors of the composed disk. This is useful for modeling differencing VHDs, the RAM diff disk, and the upcoming sqlite-backed disk. It can be used to providing disk snapshots and read and write caches. In this PR, only the RAM disk and the full disk layers are defined.
| buffers: &'a RequestBuffers<'_>, | ||
| sector: u64, | ||
| bitmap: SectorMarker<'a>, | ||
| ) -> Pin<Box<dyn 'a + Future<Output = Result<(), DiskError>> + Send>> { |
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shouldn't these be using StackFuture?
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Ehh. We need to reevaluate StackFuture anyway, since a lot has changed since we started using it in OpenHCL.
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| bits_set += range.set_count(); | ||
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| // TODO: populate read cache(s). Note that we need to detect |
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I have no qualms with this TODO, since I don't actually need read cache functionality for some of the test infra stuff I want to hack on. migrating certain test infra over to blob_disk would be great, but it continues to be non-critical
| /// | ||
| /// FUTURE: allocate shared memory here so that the disk can be migrated between | ||
| /// processes. | ||
| #[derive(MeshPayload)] | ||
| pub struct RamDiskHandle { |
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We could consider keeping this around as a special case.
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I'm ok with a bit of aliasing in cases of common disk configurations that just-so-happen to use LayeredDisk under-the-hood. i.e: I would probably have SqlDisk also have its own handle
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I dunno. That seems like a lot of redundancy if you're going to do it for SqlDisk, too.
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in that case, I'd avoid special-casing anything
| lower: disk_open(inner, true)?, | ||
| Resource::new(disk_backend_resources::LayeredDiskHandle { | ||
| layers: vec
| use disk_backend::layered::LayeredDisk; | ||
| use disk_backend::layered::SectorMarker; | ||
| use disk_backend::layered::UnmapBehavior; | ||
| use disk_backend::layered::WriteNoOverwrite; | ||
| use disk_backend::zerodisk::InvalidGeometry; |
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this might be a good PR to fix this weird zerodisk dependency in ramdisk. not major, but a weird dep to see
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I removed zerodisk since we don't use it for anything anymore.
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I mean, it serves as a simple "null disk" example implementation, but sure, we can just add it back in the future if we ever need it...
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A few lingering comments about organization aside, this LGTM. Looking forward to rebasing #380 on top of this! |
Add a new disk type
LayeredDiskthat is composed of multiple layers, each of which can contribute an arbitrary subset of the sectors of the composed disk.This is useful for modeling differencing VHDs, the RAM diff disk, and the upcoming sqlite-backed disk. It can be used to providing disk snapshots and read and write caches.
In this PR, only the RAM disk and the full disk layers are defined.