config + job: forbid non-verlapping receiver root_fs

refs #136
refs #140

daemon/job/build_jobs.go

@@ -2,6 +2,9 @@ package job
 
 import (
 	"fmt"
+	"sort"
+	"strings"
+
 	"github.com/pkg/errors"
 	"github.com/zrepl/zrepl/config"
 )
@@ -18,6 +21,22 @@ func JobsFromConfig(c *config.Config) ([]Job, error) {
 		}
 		js[i] = j
 	}
+
+	// receiving-side root filesystems must not overlap
+	{
+		rfss := make([]string, len(js))
+		for i, j := range js {
+			jrfs, ok := j.OwnedDatasetSubtreeRoot()
+			if !ok {
+				continue
+			}
+			rfss[i] = jrfs.ToString()
+		}
+		if err := validateReceivingSidesDoNotOverlap(rfss); err != nil {
+			return nil, err
+		}
+	}
+
 	return js, nil
 }
 
@@ -74,3 +93,27 @@ func buildJob(c *config.Global, in config.JobEnum) (j Job, err error) {
 	return j, nil
 
 }
+
+func validateReceivingSidesDoNotOverlap(receivingRootFSs []string) error {
+	if len(receivingRootFSs) == 0 {
+		return nil
+	}
+	rfss := make([]string, len(receivingRootFSs))
+	copy(rfss, receivingRootFSs)
+	sort.Slice(rfss, func(i, j int) bool {
+		return strings.Compare(rfss[i], rfss[j]) == -1
+	})
+	// idea:
+	//   no path in rfss must be prefix of another
+	//
+	// rfss is now lexicographically sorted, which means that
+	// if i is prefix of j, i < j (in lexicographical order)
+	// thus,
+	// if any i is prefix of i+n (n >= 1), there is overlap
+	for i := 0; i < len(rfss)-1; i++ {
+		if strings.HasPrefix(rfss[i+1], rfss[i]) {
+			return fmt.Errorf("receiving jobs with overlapping root filesystems are forbidden")
+		}
+	}
+	return nil
+}