Add --read-data-subset flag to check command

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>

changelog/0.8.3/issue-1497

@@ -0,0 +1,7 @@
+Enhancement: Add --read-data-subset flag to check command
+
+This change introduces ability to check integrity of a subset of repository 
+data packs. This can be used to spread integrity check of larger repositories
+over period of time.
+
+https://github.com/restic/restic/issues/1497

cmd/restic/cmd_check.go

@@ -3,6 +3,8 @@ package main
 import (
 	"fmt"
 	"os"
+	"strconv"
+	"strings"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -26,11 +28,15 @@ repository and not use a local cache.
 	RunE: func(cmd *cobra.Command, args []string) error {
 		return runCheck(checkOptions, globalOptions, args)
 	},
+	PreRunE: func(cmd *cobra.Command, args []string) error {
+		return checkFlags(checkOptions)
+	},
 }
 
 // CheckOptions bundles all options for the 'check' command.
 type CheckOptions struct {
 	ReadData       bool
+	ReadDataSubset string
 	CheckUnused    bool
 	WithCache      bool
 }
@@ -42,10 +48,45 @@ func init() {
 
 	f := cmdCheck.Flags()
 	f.BoolVar(&checkOptions.ReadData, "read-data", false, "read all data blobs")
+	f.StringVar(&checkOptions.ReadDataSubset, "read-data-subset", "", "read subset of data packs")
 	f.BoolVar(&checkOptions.CheckUnused, "check-unused", false, "find unused blobs")
 	f.BoolVar(&checkOptions.WithCache, "with-cache", false, "use the cache")
 }
 
+func checkFlags(opts CheckOptions) error {
+	if opts.ReadData && opts.ReadDataSubset != "" {
+		return errors.Fatalf("check flags --read-data and --read-data-subset cannot be used together")
+	}
+	if opts.ReadDataSubset != "" {
+		dataSubset, err := stringToIntSlice(opts.ReadDataSubset)
+		if err != nil || len(dataSubset) != 2 {
+			return errors.Fatalf("check flag --read-data-subset must have two positive integer values, e.g. --read-data-subset=1/2")
+		}
+		if dataSubset[0] == 0 || dataSubset[1] == 0 || dataSubset[0] > dataSubset[1] {
+			return errors.Fatalf("check flag --read-data-subset=n/t values must be positive integers, and n <= t, e.g. --read-data-subset=1/2")
+		}
+	}
+
+	return nil
+}
+
+// stringToIntSlice converts string to []uint, using '/' as element separator
+func stringToIntSlice(param string) (split []uint, err error) {
+	if param == "" {
+		return nil, nil
+	}
+	parts := strings.Split(param, "/")
+	result := make([]uint, len(parts))
+	for idx, part := range parts {
+		uintval, err := strconv.ParseUint(part, 10, 0)
+		if err != nil {
+			return nil, err
+		}
+		result[idx] = uint(uintval)
+	}
+	return result, nil
+}
+
 func newReadProgress(gopts GlobalOptions, todo restic.Stat) *restic.Progress {
 	if gopts.Quiet {
 		return nil
@@ -158,13 +199,25 @@ func runCheck(opts CheckOptions, gopts GlobalOptions, args []string) error {
 		}
 	}
 
-	if opts.ReadData {
-		Verbosef("read all data\n")
+	doReadData := func(bucket, totalBuckets uint) {
+		packs := restic.IDSet{}
+		for pack := range chkr.GetPacks() {
+			if (uint(pack[0]) % totalBuckets) == (bucket - 1) {
+				packs.Insert(pack)
+			}
+		}
+		packCount := uint64(len(packs))
 
-		p := newReadProgress(gopts, restic.Stat{Blobs: chkr.CountPacks()})
+		if packCount < chkr.CountPacks() {
+			Verbosef(fmt.Sprintf("read group #%d of %d data packs (out of total %d packs in %d groups)\n", bucket, packCount, chkr.CountPacks(), totalBuckets))
+		} else {
+			Verbosef("read all data\n")
+		}
+
+		p := newReadProgress(gopts, restic.Stat{Blobs: packCount})
 		errChan := make(chan error)
 
-		go chkr.ReadData(gopts.ctx, p, errChan)
+		go chkr.ReadPacks(gopts.ctx, packs, p, errChan)
 
 		for err := range errChan {
 			errorsFound = true
@@ -172,6 +225,14 @@ func runCheck(opts CheckOptions, gopts GlobalOptions, args []string) error {
 		}
 	}
 
+	switch {
+	case opts.ReadData:
+		doReadData(1, 1)
+	case opts.ReadDataSubset != "":
+		dataSubset, _ := stringToIntSlice(opts.ReadDataSubset)
+		doReadData(dataSubset[0], dataSubset[1])
+	}
+
 	if errorsFound {
 		return errors.Fatal("repository contains errors")
 	}

doc/045_working_with_repos.rst

@@ -87,3 +87,29 @@ yield the same error:
     Load indexes
     ciphertext verification failed
 
+By default, ``check`` command does not check that repository data files 
+are unmodified. Use ``--read-data`` parameter to check all repository
+data files:
+
+.. code-block:: console
+
+    $ restic -r /tmp/backup check --read-data
+    load indexes
+    check all packs
+    check snapshots, trees and blobs
+    read all data
+
+Use ``--read-data-subset=n/t`` parameter to check subset of repository data
+files. The parameter takes two values, ``n`` and ``t``. All repository data 
+files are logically devided in ``t`` roughly equal groups and only files that
+belong to the group number ``n`` are checked. For example, the following 
+commands check all repository data files over 5 separate invocations:
+
+.. code-block:: console
+
+    $ restic -r /tmp/backup check --read-data-subset=1/5
+    $ restic -r /tmp/backup check --read-data-subset=2/5
+    $ restic -r /tmp/backup check --read-data-subset=3/5
+    $ restic -r /tmp/backup check --read-data-subset=4/5
+    $ restic -r /tmp/backup check --read-data-subset=5/5
+

internal/checker/checker.go

@@ -622,6 +622,11 @@ func (c *Checker) CountPacks() uint64 {
 	return uint64(len(c.packs))
 }
 
+// GetPacks returns IDSet of packs in the repository
+func (c *Checker) GetPacks() restic.IDSet {
+	return c.packs
+}
+
 // checkPack reads a pack and checks the integrity of all blobs.
 func checkPack(ctx context.Context, r restic.Repository, id restic.ID) error {
 	debug.Log("checking pack %v", id)
@@ -697,6 +702,11 @@ func checkPack(ctx context.Context, r restic.Repository, id restic.ID) error {
 
 // ReadData loads all data from the repository and checks the integrity.
 func (c *Checker) ReadData(ctx context.Context, p *restic.Progress, errChan chan<- error) {
+	c.ReadPacks(ctx, c.packs, p, errChan)
+}
+
+// ReadPacks loads data from specified packs and checks the integrity.
+func (c *Checker) ReadPacks(ctx context.Context, packs restic.IDSet, p *restic.Progress, errChan chan<- error) {
 	defer close(errChan)
 
 	p.Start()
@@ -705,18 +715,6 @@ func (c *Checker) ReadData(ctx context.Context, p *restic.Progress, errChan chan
 	g, ctx := errgroup.WithContext(ctx)
 	ch := make(chan restic.ID)
 
-	// start producer for channel ch
-	g.Go(func() error {
-		defer close(ch)
-		return c.repo.List(ctx, restic.DataFile, func(id restic.ID, size int64) error {
-			select {
-			case <-ctx.Done():
-			case ch <- id:
-			}
-			return nil
-		})
-	})
-
 	// run workers
 	for i := 0; i < defaultParallelism; i++ {
 		g.Go(func() error {
@@ -748,6 +746,15 @@ func (c *Checker) ReadData(ctx context.Context, p *restic.Progress, errChan chan
 		})
 	}
 
+	// push packs to ch
+	for pack := range packs {
+		select {
+		case ch <- pack:
+		case <-ctx.Done():
+		}
+	}
+	close(ch)
+
 	err := g.Wait()
 	if err != nil {
 		select {