func (f *rwFolder) pullerRoutine(in <-chan pullBlockState, out chan<- *sharedPullerState) {
	for state := range in {
		if state.failed() != nil {
			out <- state.sharedPullerState
			continue
		}

		// Get an fd to the temporary file. Technically we don't need it until
		// after fetching the block, but if we run into an error here there is
		// no point in issuing the request to the network.
		fd, err := state.tempFile()
		if err != nil {
			out <- state.sharedPullerState
			continue
		}

		if f.allowSparse && state.reused == 0 && state.block.IsEmpty() {
			// There is no need to request a block of all zeroes. Pretend we
			// requested it and handled it correctly.
			state.pullDone(state.block)
			out <- state.sharedPullerState
			continue
		}

		var lastError error
		candidates := f.model.Availability(f.folderID, state.file.Name, state.file.Version, state.block)
		for {
			// Select the least busy device to pull the block from. If we found no
			// feasible device at all, fail the block (and in the long run, the
			// file).
			selected, found := activity.leastBusy(candidates)
			if !found {
				if lastError != nil {
					state.fail("pull", lastError)
				} else {
					state.fail("pull", errNoDevice)
				}
				break
			}

			candidates = removeAvailability(candidates, selected)

			// Fetch the block, while marking the selected device as in use so that
			// leastBusy can select another device when someone else asks.
			activity.using(selected)
			buf, lastError := f.model.requestGlobal(selected.ID, f.folderID, state.file.Name, state.block.Offset, int(state.block.Size), state.block.Hash, selected.FromTemporary)
			activity.done(selected)
			if lastError != nil {
				l.Debugln("request:", f.folderID, state.file.Name, state.block.Offset, state.block.Size, "returned error:", lastError)
				continue
			}

			// Verify that the received block matches the desired hash, if not
			// try pulling it from another device.
			_, lastError = scanner.VerifyBuffer(buf, state.block)
			if lastError != nil {
				l.Debugln("request:", f.folderID, state.file.Name, state.block.Offset, state.block.Size, "hash mismatch")
				continue
			}

			// Save the block data we got from the cluster
			_, err = fd.WriteAt(buf, state.block.Offset)
			if err != nil {
				state.fail("save", err)
			} else {
				state.pullDone(state.block)
			}
			break
		}
		out <- state.sharedPullerState
	}
}

func (p *rwFolder) pullerRoutine(in <-chan pullBlockState, out chan<- *sharedPullerState) {
	for state := range in {
		if state.failed() != nil {
			out <- state.sharedPullerState
			continue
		}

		// Get an fd to the temporary file. Technically we don't need it until
		// after fetching the block, but if we run into an error here there is
		// no point in issuing the request to the network.
		fd, err := state.tempFile()
		if err != nil {
			out <- state.sharedPullerState
			continue
		}

		var lastError error
		potentialDevices := p.model.Availability(p.folder, state.file.Name)
		for {
			// Select the least busy device to pull the block from. If we found no
			// feasible device at all, fail the block (and in the long run, the
			// file).
			selected := activity.leastBusy(potentialDevices)
			if selected == (protocol.DeviceID{}) {
				if lastError != nil {
					state.fail("pull", lastError)
				} else {
					state.fail("pull", errNoDevice)
				}
				break
			}

			potentialDevices = removeDevice(potentialDevices, selected)

			// Fetch the block, while marking the selected device as in use so that
			// leastBusy can select another device when someone else asks.
			activity.using(selected)
			buf, lastError := p.model.requestGlobal(selected, p.folder, state.file.Name, state.block.Offset, int(state.block.Size), state.block.Hash, 0, nil)
			activity.done(selected)
			if lastError != nil {
				if debug {
					l.Debugln("request:", p.folder, state.file.Name, state.block.Offset, state.block.Size, "returned error:", lastError)
				}
				continue
			}

			// Verify that the received block matches the desired hash, if not
			// try pulling it from another device.
			_, lastError = scanner.VerifyBuffer(buf, state.block)
			if lastError != nil {
				if debug {
					l.Debugln("request:", p.folder, state.file.Name, state.block.Offset, state.block.Size, "hash mismatch")
				}
				continue
			}

			// Save the block data we got from the cluster
			_, err = fd.WriteAt(buf, state.block.Offset)
			if err != nil {
				state.fail("save", err)
			} else {
				state.pullDone()
			}
			break
		}
		out <- state.sharedPullerState
	}
}

// copierRoutine reads copierStates until the in channel closes and performs
// the relevant copies when possible, or passes it to the puller routine.
func (f *rwFolder) copierRoutine(in <-chan copyBlocksState, pullChan chan<- pullBlockState, out chan<- *sharedPullerState) {
	buf := make([]byte, protocol.BlockSize)

	for state := range in {
		dstFd, err := state.tempFile()
		if err != nil {
			// Nothing more to do for this failed file, since we couldn't create a temporary for it.
			out <- state.sharedPullerState
			continue
		}

		if f.model.progressEmitter != nil {
			f.model.progressEmitter.Register(state.sharedPullerState)
		}

		folderRoots := make(map[string]string)
		var folders []string
		f.model.fmut.RLock()
		for folder, cfg := range f.model.folderCfgs {
			folderRoots[folder] = cfg.Path()
			folders = append(folders, folder)
		}
		f.model.fmut.RUnlock()

		for _, block := range state.blocks {
			if f.allowSparse && state.reused == 0 && block.IsEmpty() {
				// The block is a block of all zeroes, and we are not reusing
				// a temp file, so there is no need to do anything with it.
				// If we were reusing a temp file and had this block to copy,
				// it would be because the block in the temp file was *not* a
				// block of all zeroes, so then we should not skip it.

				// Pretend we copied it.
				state.copiedFromOrigin()
				continue
			}

			buf = buf[:int(block.Size)]
			found := f.model.finder.Iterate(folders, block.Hash, func(folder, file string, index int32) bool {
				inFile, err := rootedJoinedPath(folderRoots[folder], file)
				if err != nil {
					return false
				}
				fd, err := os.Open(inFile)
				if err != nil {
					return false
				}

				_, err = fd.ReadAt(buf, protocol.BlockSize*int64(index))
				fd.Close()
				if err != nil {
					return false
				}

				hash, err := scanner.VerifyBuffer(buf, block)
				if err != nil {
					if hash != nil {
						l.Debugf("Finder block mismatch in %s:%s:%d expected %q got %q", folder, file, index, block.Hash, hash)
						err = f.model.finder.Fix(folder, file, index, block.Hash, hash)
						if err != nil {
							l.Warnln("finder fix:", err)
						}
					} else {
						l.Debugln("Finder failed to verify buffer", err)
					}
					return false
				}

				_, err = dstFd.WriteAt(buf, block.Offset)
				if err != nil {
					state.fail("dst write", err)
				}
				if file == state.file.Name {
					state.copiedFromOrigin()
				}
				return true
			})

			if state.failed() != nil {
				break
			}

			if !found {
				state.pullStarted()
				ps := pullBlockState{
					sharedPullerState: state.sharedPullerState,
					block:             block,
				}
				pullChan <- ps
			} else {
				state.copyDone(block)
			}
		}
		out <- state.sharedPullerState
	}
}

// copierRoutine reads copierStates until the in channel closes and performs
// the relevant copies when possible, or passes it to the puller routine.
func (p *rwFolder) copierRoutine(in <-chan copyBlocksState, pullChan chan<- pullBlockState, out chan<- *sharedPullerState) {
	buf := make([]byte, protocol.BlockSize)

	for state := range in {
		dstFd, err := state.tempFile()
		if err != nil {
			// Nothing more to do for this failed file, since we couldn't create a temporary for it.
			out <- state.sharedPullerState
			continue
		}

		if p.progressEmitter != nil {
			p.progressEmitter.Register(state.sharedPullerState)
		}

		folderRoots := make(map[string]string)
		p.model.fmut.RLock()
		for folder, cfg := range p.model.folderCfgs {
			folderRoots[folder] = cfg.Path()
		}
		p.model.fmut.RUnlock()

		for _, block := range state.blocks {
			buf = buf[:int(block.Size)]
			found := p.model.finder.Iterate(block.Hash, func(folder, file string, index int32) bool {
				fd, err := os.Open(filepath.Join(folderRoots[folder], file))
				if err != nil {
					return false
				}

				_, err = fd.ReadAt(buf, protocol.BlockSize*int64(index))
				fd.Close()
				if err != nil {
					return false
				}

				hash, err := scanner.VerifyBuffer(buf, block)
				if err != nil {
					if hash != nil {
						if debug {
							l.Debugf("Finder block mismatch in %s:%s:%d expected %q got %q", folder, file, index, block.Hash, hash)
						}
						err = p.model.finder.Fix(folder, file, index, block.Hash, hash)
						if err != nil {
							l.Warnln("finder fix:", err)
						}
					} else if debug {
						l.Debugln("Finder failed to verify buffer", err)
					}
					return false
				}

				_, err = dstFd.WriteAt(buf, block.Offset)
				if err != nil {
					state.fail("dst write", err)
				}
				if file == state.file.Name {
					state.copiedFromOrigin()
				}
				return true
			})

			if state.failed() != nil {
				break
			}

			if !found {
				state.pullStarted()
				ps := pullBlockState{
					sharedPullerState: state.sharedPullerState,
					block:             block,
				}
				pullChan <- ps
			} else {
				state.copyDone()
			}
		}
		out <- state.sharedPullerState
	}
}