On 10.09.19 11:22, Vladimir Sementsov-Ogievskiy wrote: [...]
> Ok, than > > 4. Postpone improvements for a follow-up (anyway, finally, block-copy should > use block_status to copy by larger chunks, like mirror does), and improve the > comment like this: > > """ > Used for job sync=top mode, which currently works as follows (the size of the > comment definitely shows unclean design, but this is a TODO to improve it): > If job started in sync=top mode, which means that we want to copy only parts > allocated in top layer, job should behave like this: > > 1. Create block-copy state with skip_unallocated = true. > 2. Then, block_copy() will automatically check for allocation in top layer, > and do not copy areas which are not allocated in top layer. So, for example, > copy-before-write operations in backup works correctly even before [3.] > 3. Sequentially call block_copy_reset_unallocated() to cover the whole source > node, copy_bitmap will be updated correspondingly. > 4. Unset skip_unallocated variable in block-copy state, to avoid extra (as > everything is covered by [3.]) block-status queries in block_copy() calls > 5. Do sequential copying by loop of block_copy() calls, all needed allocation > information is already in copy_bitmap. > > From block_copy() side, it behaves like this: > If skip_unallocated is set, block_copy() will reset in copy_bitmap areas > unallocated in top image (so they will not be copied). Whenever any such > area is cleared, progress_reset_callback will be invoked. Note, that > progress_reset_callback is called from block_copy_reset_unallocated() too. > """ Can this not be simplified? """ Used by sync=top jobs, which first scan the source node for unallocated areas and clear them in the copy_bitmap. During this process, the bitmap is thus not fully initialized: It may still have bits set for areas that are unallocated and should actually not be copied. This is indicated by skip_unallocated. In this case, block_copy() will query the source’s allocation status, skip unallocated regions, clear them in the copy_bitmap, and invoke block_copy_reset_unallocated() every time it does. Otherwise, block_copy() copies everything that’s dirty in the copy_bitmap. """ Max
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