Don't require free disk space when we might only update metadata

Instead, make sure we do the check as part of CheckFolderHealth before
pulling, and individually per file to try to not run out of space at
that stage.

(The latter is far from fool proof as we may pull lots of stuff in
parallell, but it's worth a try.)

lib/model/rwfolder.go

@@ -212,6 +212,12 @@ func (p *rwFolder) Serve() {
 				continue
 			}
 
+			if err := p.model.CheckFolderHealth(p.folder); err != nil {
+				l.Infoln("Skipping folder", p.folder, "pull due to folder error:", err)
+				p.pullTimer.Reset(nextPullIntv)
+				continue
+			}
+
 			p.model.fmut.RLock()
 			curIgnores := p.model.folderIgnores[p.folder]
 			p.model.fmut.RUnlock()
@@ -451,7 +457,6 @@ func (p *rwFolder) pullerIteration(ignores *ignore.Matcher) int {
 	// !!!
 
 	changed := 0
-	pullFileSize := int64(0)
 
 	fileDeletions := map[string]protocol.FileInfo{}
 	dirDeletions := []protocol.FileInfo{}
@@ -500,7 +505,6 @@ func (p *rwFolder) pullerIteration(ignores *ignore.Matcher) int {
 		default:
 			// A new or changed file or symlink. This is the only case where we
 			// do stuff concurrently in the background
-			pullFileSize += file.Size()
 			p.queue.Push(file.Name, file.Size(), file.Modified)
 		}
 
@@ -508,16 +512,6 @@ func (p *rwFolder) pullerIteration(ignores *ignore.Matcher) int {
 		return true
 	})
 
-	// Check if we are able to store all files on disk. Only perform this
-	// check if there is a minimum free space threshold set on the folder.
-	folderCfg := p.model.cfg.Folders()[p.folder]
-	if folderCfg.MinDiskFreePct > 0 && pullFileSize > 0 {
-		if free, err := osutil.DiskFreeBytes(folderCfg.Path()); err == nil && free < pullFileSize {
-			l.Warnf(`Folder "%s": insufficient disk space available to pull %d files (%.2f MiB)`, p.folder, changed, float64(pullFileSize)/1024/1024)
-			return 0
-		}
-	}
-
 	// Reorder the file queue according to configuration
 
 	switch p.order {
@@ -970,6 +964,12 @@ func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocks
 		return
 	}
 
+	if free, err := osutil.DiskFreeBytes(p.dir); err == nil && free < file.Size() {
+		l.Warnf(`Folder "%s": insufficient disk space in %s for %s: have %.2f MiB, need %.2f MiB`, p.dir, file.Name, float64(free)/1024/1024, float64(file.Size())/1024/1024)
+		p.newError(file.Name, errors.New("insufficient space"))
+		return
+	}
+
 	events.Default.Log(events.ItemStarted, map[string]string{
 		"folder": p.folder,
 		"item":   file.Name,