Reflink support about btrfs HOT 6 CLOSED

Yep, it's on my list! Probably not the next version, but the one after that.

I don't think there's an existing Windows ioctl I can co-opt though... I'm not sure FSCTL_SIS_COPYFILE does what we need it to. You might have to patch your program to get it to use the right fsctl.

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@maharmstone Windows 10 & Server 2016 has FSCTL_DUPLICATE_EXTENTS_TO_FILE, and FILE_SUPPORTS_BLOCK_REFCOUNTING indicating that filesystem supports it.
This FSCTL is similar to BTRFS_IOC_CLONE_RANGE.
Veeam Backup & Replication software and Hyper-V version 2016 is already using this.

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Thank you, that looks promising.

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This is fully implemented now, and will be available in the next version.

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@maharmstone I'm sorry because I found a critical bug in my reflink code that you referenced. Using FILE_STANDARD_INFO::AllocationSize is not correct when sparse file. When sparse, AllocationSize is size on disk, not round up-ed file size to cluster size.

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Thank you - you're right, I wasn't aware of that. Confusingly, it seems that the AllocationSize in the FCB header isn't necessarily the same as the AllocationSize returned by QueryStandardInfo etc. I've fixed it now: 5347e4b

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