remote.uncache, remote.meta.sync, remote.cache: keep local writes that land while they run (#12382)

* remote.uncache: skip a file overwritten since the walk read it

The uncache cleared the chunks of the entry its directory walk returned and
wrote it back unconditionally. A file overwritten after the walk read it
was reset to the remote pointer, and its new chunks were dropped, so an
acknowledged write was lost. Write back only while the filer still holds
the entry as read, and report the file as skipped otherwise.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* remote.meta.sync: keep files written locally after the directory listing

meta.sync lists each local directory once and works from that listing.
A changed remote file was written back over the listed entry
unconditionally, and a name missing from the listing was created without
O_EXCL, so a file written locally in between was replaced by the remote
pointer either way. Update only while the filer still holds the listed
entry, create exclusively, and report such files as skipped. The create
now also surfaces errors the filer returns in its response.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* remote.cache: keep files written locally after the lookup

The metadata step looks each file up and then either rewrites it from the
remote unconditionally or creates it without O_EXCL, so a local write
landing between the lookup and the write was replaced by the remote
pointer. Reuse doSaveRemoteEntry, which updates only while the filer still
holds the looked-up entry, create exclusively, and report such files as
skipped.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* remote.meta.sync: do not descend into a name a local file took

When the exclusive create of a remote directory finds the name taken, the
sync still descended into it, and creating the remote children under a
local file would turn that file into a directory. Descend only when the
name now holds a directory.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* remote.meta.sync: delete only the file version it listed

The type-change and -deleteStale paths removed a remote-backed file
unconditionally, so a local write landing after the directory listing was
deleted with it. Condition the delete on the listed mtime, as fs.verify
and volume.fsck do; the filer then keeps a file written since.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* remote.meta.sync: condition directory and mtime-less deletes too

The listed-mtime cutoff was only sent for files, so a remote-backed
directory replaced locally by a file between the emptiness check and the
delete was removed unconditionally, and so was a file listed without an
mtime. Send the cutoff for directories as well, and for an entry listed
without an mtime keep it once a write has set one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* filer: test that DeleteEntry applies the request's mtime cutoff

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* remote.meta.sync: keep the listed nanoseconds as the cutoff of an epoch mtime

An entry listed at the epoch with a sub-second mtime was sent a 1 ns
cutoff, so the filer kept it unchanged although the old code deleted it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* remote.meta.sync: report an entry the filer kept instead of deleting it

The filer answers a delete it skipped under the mtime cutoff with
success, so the sync printed (delete) for an entry a local write kept.
deleteLocalEntry now looks the name up after the delete and prints the
outcome, and a replaced file that was kept is not recreated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/shell/command_remote_cache.go

@@ -2,6 +2,7 @@ package shell
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -260,7 +261,7 @@ func (c *commandRemoteCache) doComprehensiveSync(commandEnv *CommandEnv, writer
 			isDirectory := remoteEntry.RemoteSize == 0 && remoteEntry.RemoteMtime == 0
 			if lookupErr == filer_pb.ErrNotFound {
 				// Create new entry
-				_, createErr := client.CreateEntry(ctx, &filer_pb.CreateEntryRequest{
+				createErr := filer_pb.CreateEntry(ctx, client, &filer_pb.CreateEntryRequest{
 					Directory: string(localDir),
 					Entry: &filer_pb.Entry{
 						Name:        name,
@@ -273,7 +274,12 @@ func (c *commandRemoteCache) doComprehensiveSync(commandEnv *CommandEnv, writer
 						Extended:    filer.MergeRemoteContentEncoding(remoteEntry, nil),
 						RemoteEntry: remoteEntry,
 					},
+					OExcl: true,
 				})
+				if errors.Is(createErr, filer_pb.ErrEntryAlreadyExists) {
+					fmt.Fprintf(writer, "skipped (created since it was looked up)\n")
+					continue
+				}
 				if createErr != nil {
 					fmt.Fprintf(writer, "failed to create: %v\n", createErr)
 					continue
@@ -287,18 +293,11 @@ func (c *commandRemoteCache) doComprehensiveSync(commandEnv *CommandEnv, writer
 					continue
 				}
 
-				existingEntry.RemoteEntry = remoteEntry
-				existingEntry.Attributes.FileSize = uint64(remoteEntry.RemoteSize)
-				existingEntry.Attributes.Mtime = remoteEntry.RemoteMtime
-				existingEntry.Attributes.Md5 = nil
-				existingEntry.Extended = filer.MergeRemoteContentEncoding(remoteEntry, existingEntry.Extended)
-				existingEntry.Chunks = nil
-				existingEntry.Content = nil
-
-				_, updateErr := client.UpdateEntry(ctx, &filer_pb.UpdateEntryRequest{
-					Directory: string(localDir),
-					Entry:     existingEntry,
-				})
+				stale, updateErr := doSaveRemoteEntry(client, string(localDir), existingEntry, remoteEntry)
+				if stale {
+					fmt.Fprintf(writer, "skipped (changed since it was looked up)\n")
+					continue
+				}
 				if updateErr != nil {
 					fmt.Fprintf(writer, "failed to update: %v\n", updateErr)
 					continue

weed/shell/command_remote_meta_sync.go

@@ -2,6 +2,7 @@ package shell
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -214,10 +215,13 @@ func pullMetadataDirectory(ctx context.Context, client filer_pb.SeaweedFilerClie
 					continue
 				}
 			} else {
-				fmt.Fprintf(writer, "%s (delete)\n", localPath)
-				if err := deleteLocalEntry(ctx, client, localDir, name); err != nil {
+				kept, err := deleteLocalEntry(ctx, client, writer, localDir, existingEntry)
+				if err != nil {
 					return err
 				}
+				if kept {
+					continue
+				}
 			}
 			existingEntry = nil
 		}
@@ -240,9 +244,20 @@ func pullMetadataDirectory(ctx context.Context, client filer_pb.SeaweedFilerClie
 		}
 
 		if existingEntry == nil {
-			if err := createRemoteEntry(ctx, client, writer, localDir, name, child, remoteLoc.Name); err != nil {
+			taken, err := createRemoteEntry(ctx, client, writer, localDir, name, child, remoteLoc.Name)
+			if err != nil {
 				return err
 			}
+			if taken && child.isDirectory {
+				// descending into a name a local file took would turn it into a directory
+				resp, err := filer_pb.LookupEntry(ctx, client, &filer_pb.LookupDirectoryEntryRequest{Directory: string(localDir), Name: name})
+				if err != nil && !errors.Is(err, filer_pb.ErrNotFound) {
+					return err
+				}
+				if resp == nil || !resp.Entry.IsDirectory {
+					continue
+				}
+			}
 		} else if !child.isDirectory {
 			if existingEntry.RemoteEntry == nil {
 				// a local change that should not be overwritten
@@ -255,9 +270,13 @@ func pullMetadataDirectory(ctx context.Context, client filer_pb.SeaweedFilerClie
 				// persist the stat-derived encoding so the next run skips the stat
 				(statFiles && existingEntry.RemoteEntry.RemoteContentEncoding == nil &&
 					child.remoteEntry.RemoteContentEncoding != nil) {
-				fmt.Fprintf(writer, "%s (update)\n", localPath)
-				if err := doSaveRemoteEntry(client, string(localDir), existingEntry, child.remoteEntry); err != nil {
+				stale, err := doSaveRemoteEntry(client, string(localDir), existingEntry, child.remoteEntry)
+				if stale {
+					fmt.Fprintf(writer, "%s (skip, changed since listed)\n", localPath)
+				} else if err != nil {
 					return err
+				} else {
+					fmt.Fprintf(writer, "%s (update)\n", localPath)
 				}
 			} else {
 				fmt.Fprintf(writer, "%s (skip)\n", localPath)
@@ -297,8 +316,8 @@ func deleteRemoteBackedEntry(ctx context.Context, client filer_pb.SeaweedFilerCl
 		if existingEntry.RemoteEntry == nil {
 			return nil
 		}
-		fmt.Fprintf(writer, "%s (delete)\n", localPath)
-		return deleteLocalEntry(ctx, client, localDir, name)
+		_, err := deleteLocalEntry(ctx, client, writer, localDir, existingEntry)
+		return err
 	}
 
 	children, err := listLocalDirectory(ctx, client, localPath)
@@ -319,14 +338,35 @@ func deleteRemoteBackedEntry(ctx context.Context, client filer_pb.SeaweedFilerCl
 		return err
 	}
 	if empty {
-		fmt.Fprintf(writer, "%s (delete)\n", localPath)
-		return deleteLocalEntry(ctx, client, localDir, name)
+		_, err = deleteLocalEntry(ctx, client, writer, localDir, existingEntry)
 	}
-	return nil
+	return err
 }
 
-func deleteLocalEntry(ctx context.Context, client filer_pb.SeaweedFilerClient, localDir util.FullPath, name string) error {
-	return filer_pb.DoRemove(ctx, client, string(localDir), name, true, false, false, false, nil)
+// deleteLocalEntry removes the entry as it was listed; the filer keeps an entry
+// whose mtime a local write has moved past the listed one, reported as kept.
+// An entry listed without an mtime is kept once a write sets one.
+func deleteLocalEntry(ctx context.Context, client filer_pb.SeaweedFilerClient, writer io.Writer, localDir util.FullPath, entry *filer_pb.Entry) (kept bool, err error) {
+	req := &filer_pb.DeleteEntryRequest{Directory: string(localDir), Name: entry.Name, IsDeleteData: true}
+	var ok bool
+	req.IfNotModifiedAfter, req.IfNotModifiedAfterNs, ok = deleteEntryCutoff(entry.Attributes.GetMtime(), entry.Attributes.GetMtimeNs())
+	if !ok {
+		req.IfNotModifiedAfterNs = max(1, int64(entry.Attributes.GetMtimeNs()))
+	}
+	if _, err = filer_pb.DoRemoveRequest(ctx, client, req); err != nil {
+		return false, err
+	}
+	localPath := localDir.Child(entry.Name)
+	_, err = filer_pb.LookupEntry(ctx, client, &filer_pb.LookupDirectoryEntryRequest{Directory: string(localDir), Name: entry.Name})
+	if err == nil {
+		fmt.Fprintf(writer, "%s (skip, changed since listed)\n", localPath)
+		return true, nil
+	}
+	if !errors.Is(err, filer_pb.ErrNotFound) {
+		return false, err
+	}
+	fmt.Fprintf(writer, "%s (delete)\n", localPath)
+	return false, nil
 }
 
 func isLocalDirectoryEmpty(ctx context.Context, client filer_pb.SeaweedFilerClient, dir util.FullPath) (bool, error) {
@@ -338,7 +378,9 @@ func isLocalDirectoryEmpty(ctx context.Context, client filer_pb.SeaweedFilerClie
 	return empty, err
 }
 
-func createRemoteEntry(ctx context.Context, client filer_pb.SeaweedFilerClient, writer io.Writer, localDir util.FullPath, name string, child *remoteChild, storageName string) error {
+// createRemoteEntry creates the entry only if the name is still free; taken
+// reports that something was created there after the directory was listed.
+func createRemoteEntry(ctx context.Context, client filer_pb.SeaweedFilerClient, writer io.Writer, localDir util.FullPath, name string, child *remoteChild, storageName string) (taken bool, err error) {
 	attributes := &filer_pb.FuseAttributes{
 		FileMode: remoteEntryFileMode(child.isDirectory),
 		TtlSec:   0, // Remote entries should not have TTL
@@ -356,7 +398,7 @@ func createRemoteEntry(ctx context.Context, client filer_pb.SeaweedFilerClient,
 		attributes.FileSize = uint64(child.remoteEntry.RemoteSize)
 		attributes.Mtime = child.remoteEntry.RemoteMtime
 	}
-	_, err := client.CreateEntry(ctx, &filer_pb.CreateEntryRequest{
+	err = filer_pb.CreateEntry(ctx, client, &filer_pb.CreateEntryRequest{
 		Directory: string(localDir),
 		Entry: &filer_pb.Entry{
 			Name:        name,
@@ -365,9 +407,17 @@ func createRemoteEntry(ctx context.Context, client filer_pb.SeaweedFilerClient,
 			Extended:    filer.MergeRemoteContentEncoding(remoteEntry, nil),
 			RemoteEntry: remoteEntry,
 		},
+		OExcl: true,
 	})
+	if errors.Is(err, filer_pb.ErrEntryAlreadyExists) {
+		fmt.Fprintf(writer, "%s (skip, created since listed)\n", localDir.Child(name))
+		return true, nil
+	}
+	if err != nil {
+		return false, err
+	}
 	fmt.Fprintf(writer, "%s (create)\n", localDir.Child(name))
-	return err
+	return false, nil
 }
 
 func childRemoteLocation(remoteLoc *remote_pb.RemoteStorageLocation, name string) *remote_pb.RemoteStorageLocation {

weed/shell/command_remote_meta_sync_test.go

@@ -0,0 +1,245 @@
+package shell
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+	"github.com/seaweedfs/seaweedfs/weed/pb/remote_pb"
+	"github.com/seaweedfs/seaweedfs/weed/remote_storage"
+	"github.com/seaweedfs/seaweedfs/weed/util"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/proto"
+)
+
+type exclusiveCreateFiler struct {
+	filer_pb.SeaweedFilerClient
+	resp *filer_pb.CreateEntryResponse
+	req  *filer_pb.CreateEntryRequest
+}
+
+func (s *exclusiveCreateFiler) CreateEntry(_ context.Context, req *filer_pb.CreateEntryRequest, _ ...grpc.CallOption) (*filer_pb.CreateEntryResponse, error) {
+	s.req = req
+	return s.resp, nil
+}
+
+// meta.sync updates entries from a directory listing taken once per
+// directory; a file written locally after that listing must not be reset to
+// the remote pointer.
+func TestDoSaveRemoteEntryIsConditionedOnTheListedEntry(t *testing.T) {
+	listed := &filer_pb.Entry{
+		Name:        "f",
+		Attributes:  &filer_pb.FuseAttributes{FileSize: 3, Mtime: 10},
+		Chunks:      []*filer_pb.FileChunk{{Fid: &filer_pb.FileId{VolumeId: 3, FileKey: 1, Cookie: 7}}},
+		RemoteEntry: &filer_pb.RemoteEntry{StorageName: "r", RemoteETag: "old", RemoteSize: 3, RemoteMtime: 10},
+	}
+	remote := &filer_pb.RemoteEntry{StorageName: "r", RemoteETag: "new", RemoteSize: 5, RemoteMtime: 20}
+
+	for _, tc := range []struct {
+		name  string
+		err   error
+		stale bool
+	}{
+		{"unchanged", nil, false},
+		{"written since listed", status.Error(codes.FailedPrecondition, "precondition failed"), true},
+		{"deleted since listed", status.Error(codes.NotFound, "not found"), true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			fake := &conditionalUpdateFiler{err: tc.err}
+			stale, err := doSaveRemoteEntry(fake, "/buckets/b", proto.Clone(listed).(*filer_pb.Entry), remote)
+			if stale != tc.stale || (err != nil) != (tc.err != nil) {
+				t.Fatalf("stale=%v err=%v, want stale=%v err=%v", stale, err, tc.stale, tc.err)
+			}
+			clauses := fake.req.GetCondition().GetClauses()
+			if len(clauses) != 1 || clauses[0].Kind != filer_pb.WriteCondition_IF_ENTRY_EQUAL || !proto.Equal(clauses[0].ExpectedEntry, listed) {
+				t.Fatalf("condition %v must expect the listed entry", fake.req.GetCondition())
+			}
+			written := fake.req.Entry
+			if len(written.Chunks) != 0 || !proto.Equal(written.RemoteEntry, remote) || written.Attributes.FileSize != 5 {
+				t.Fatalf("written entry %v must point at the new remote copy", written)
+			}
+		})
+	}
+}
+
+// A name missing from the listing may be created locally before meta.sync
+// gets to it; the remote-only entry must not replace it.
+func TestCreateRemoteEntryKeepsAnEntryCreatedSinceListed(t *testing.T) {
+	child := &remoteChild{remoteEntry: &filer_pb.RemoteEntry{StorageName: "r", RemoteSize: 5, RemoteMtime: 20}}
+
+	for _, tc := range []struct {
+		name   string
+		resp   *filer_pb.CreateEntryResponse
+		output string
+		err    bool
+	}{
+		{"absent", &filer_pb.CreateEntryResponse{}, "/buckets/b/f (create)", false},
+		{"created since listed", &filer_pb.CreateEntryResponse{Error: "exists", ErrorCode: filer_pb.FilerError_ENTRY_ALREADY_EXISTS}, "/buckets/b/f (skip, created since listed)", false},
+		{"refused", &filer_pb.CreateEntryResponse{Error: "read only", ErrorCode: filer_pb.FilerError_READ_ONLY}, "", true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			fake := &exclusiveCreateFiler{resp: tc.resp}
+			var out strings.Builder
+			taken, err := createRemoteEntry(context.Background(), fake, &out, util.FullPath("/buckets/b"), "f", child, "r")
+			if (err != nil) != tc.err || taken != (tc.resp.ErrorCode == filer_pb.FilerError_ENTRY_ALREADY_EXISTS) {
+				t.Fatalf("taken=%v err=%v, want error %v", taken, err, tc.err)
+			}
+			if !fake.req.OExcl {
+				t.Fatalf("create of %s must be exclusive", fake.req.Entry.Name)
+			}
+			if got := strings.TrimSpace(out.String()); got != tc.output {
+				t.Fatalf("output %q, want %q", got, tc.output)
+			}
+		})
+	}
+}
+
+type takenNameFiler struct {
+	stubFilerSvc
+	creates []string
+}
+
+func (s *takenNameFiler) CreateEntry(_ context.Context, req *filer_pb.CreateEntryRequest, _ ...grpc.CallOption) (*filer_pb.CreateEntryResponse, error) {
+	s.creates = append(s.creates, string(util.FullPath(req.Directory).Child(req.Entry.Name)))
+	return &filer_pb.CreateEntryResponse{Error: "exists", ErrorCode: filer_pb.FilerError_ENTRY_ALREADY_EXISTS}, nil
+}
+
+type listingRemote struct {
+	remote_storage.RemoteStorageClient
+	dirs map[string]map[string]bool
+}
+
+func (r *listingRemote) ListDirectory(_ context.Context, loc *remote_pb.RemoteStorageLocation, visitFn remote_storage.VisitFunc) error {
+	for name, isDirectory := range r.dirs[loc.Path] {
+		if err := visitFn(loc.Path, name, isDirectory, &filer_pb.RemoteEntry{StorageName: "r", RemoteSize: 1, RemoteMtime: 1}); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// A remote directory whose name is taken locally after the listing is only
+// descended into when the name now holds a directory: creating remote
+// children under a local file would turn that file into a directory.
+func TestPullMetadataDirectoryDescendsOnlyIntoATakenDirectory(t *testing.T) {
+	remote := &listingRemote{dirs: map[string]map[string]bool{
+		"/":     {"docs": true},
+		"/docs": {"a.txt": false},
+	}}
+	for _, tc := range []struct {
+		name    string
+		isDir   bool
+		creates []string
+	}{
+		{"taken by a file", false, []string{"/buckets/b/docs"}},
+		{"taken by a directory", true, []string{"/buckets/b/docs", "/buckets/b/docs/a.txt"}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			fake := &takenNameFiler{stubFilerSvc: stubFilerSvc{lookupResp: &filer_pb.LookupDirectoryEntryResponse{
+				Entry: &filer_pb.Entry{Name: "docs", IsDirectory: tc.isDir},
+			}}}
+			var out strings.Builder
+			loc := &remote_pb.RemoteStorageLocation{Name: "r", Bucket: "rb", Path: "/"}
+			if err := pullMetadataDirectory(context.Background(), fake, &out, remote, util.FullPath("/buckets/b"), loc, false, false); err != nil {
+				t.Fatalf("sync: %v", err)
+			}
+			if strings.Join(fake.creates, ",") != strings.Join(tc.creates, ",") {
+				t.Fatalf("creates %v, want %v", fake.creates, tc.creates)
+			}
+		})
+	}
+}
+
+type deleteRecordingFiler struct {
+	takenNameFiler
+	deletes []*filer_pb.DeleteEntryRequest
+	listing map[string][]*filer_pb.Entry
+}
+
+func (s *deleteRecordingFiler) ListEntries(_ context.Context, req *filer_pb.ListEntriesRequest, _ ...grpc.CallOption) (filer_pb.SeaweedFiler_ListEntriesClient, error) {
+	return &stubListStream{entries: s.listing[req.Directory]}, nil
+}
+
+func (s *deleteRecordingFiler) DeleteEntry(_ context.Context, req *filer_pb.DeleteEntryRequest, _ ...grpc.CallOption) (*filer_pb.DeleteEntryResponse, error) {
+	s.deletes = append(s.deletes, req)
+	return &filer_pb.DeleteEntryResponse{}, nil
+}
+
+// A remote-backed entry that meta.sync drops may be replaced locally after the
+// directory listing; the delete must only remove the listed version.
+func TestPullMetadataDirectoryDeletesOnlyTheListedFile(t *testing.T) {
+	remoteFile := &filer_pb.RemoteEntry{StorageName: "r", RemoteSize: 1, RemoteMtime: 10}
+	for _, tc := range []struct {
+		name        string
+		listed      *filer_pb.Entry
+		remote      map[string]bool
+		deleteStale bool
+		sec, ns     int64
+	}{
+		{"remote turned it into a directory", &filer_pb.Entry{Name: "f", Attributes: &filer_pb.FuseAttributes{Mtime: 10, MtimeNs: 5}, RemoteEntry: remoteFile}, map[string]bool{"f": true}, false, 10, 10e9 + 5},
+		{"gone from the remote", &filer_pb.Entry{Name: "f", Attributes: &filer_pb.FuseAttributes{Mtime: 10, MtimeNs: 5}, RemoteEntry: remoteFile}, map[string]bool{}, true, 10, 10e9 + 5},
+		{"listed without an mtime", &filer_pb.Entry{Name: "f", Attributes: &filer_pb.FuseAttributes{}, RemoteEntry: remoteFile}, map[string]bool{}, true, 0, 1},
+		{"listed at the epoch with nanoseconds", &filer_pb.Entry{Name: "f", Attributes: &filer_pb.FuseAttributes{MtimeNs: 500}, RemoteEntry: remoteFile}, map[string]bool{}, true, 0, 500},
+		{"empty directory gone from the remote", &filer_pb.Entry{Name: "f", IsDirectory: true, Attributes: &filer_pb.FuseAttributes{Mtime: 20}, RemoteEntry: &filer_pb.RemoteEntry{StorageName: "r"}}, map[string]bool{}, true, 20, 20e9},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			fake := &deleteRecordingFiler{
+				takenNameFiler: takenNameFiler{stubFilerSvc: stubFilerSvc{
+					lookupResp: &filer_pb.LookupDirectoryEntryResponse{Entry: &filer_pb.Entry{Name: "f"}},
+				}},
+				listing: map[string][]*filer_pb.Entry{"/buckets/b": {tc.listed}},
+			}
+			remote := &listingRemote{dirs: map[string]map[string]bool{"/": tc.remote}}
+			var out strings.Builder
+			loc := &remote_pb.RemoteStorageLocation{Name: "r", Bucket: "rb", Path: "/"}
+			if err := pullMetadataDirectory(context.Background(), fake, &out, remote, util.FullPath("/buckets/b"), loc, tc.deleteStale, false); err != nil {
+				t.Fatalf("sync: %v", err)
+			}
+			if len(fake.deletes) != 1 || fake.deletes[0].Name != "f" || fake.deletes[0].IfNotModifiedAfter != tc.sec || fake.deletes[0].IfNotModifiedAfterNs != tc.ns {
+				t.Fatalf("deletes %v must be conditioned on the listed mtime", fake.deletes)
+			}
+		})
+	}
+}
+
+// The filer answers a delete it skipped under the cutoff with success, so the
+// sync reports what a lookup after the delete finds.
+func TestPullMetadataDirectoryReportsAKeptEntry(t *testing.T) {
+	listed := &filer_pb.Entry{Name: "f", Attributes: &filer_pb.FuseAttributes{Mtime: 10}, RemoteEntry: &filer_pb.RemoteEntry{StorageName: "r", RemoteSize: 1, RemoteMtime: 10}}
+	for _, tc := range []struct {
+		name        string
+		remote      map[string]bool
+		deleteStale bool
+		kept        bool
+		want        string
+		creates     int
+	}{
+		{"stale file kept", map[string]bool{}, true, true, "/buckets/b/f (skip, changed since listed)\n", 0},
+		{"stale file deleted", map[string]bool{}, true, false, "/buckets/b/f (delete)\n", 0},
+		{"file replaced by a remote directory kept", map[string]bool{"f": true}, false, true, "/buckets/b/f (skip, changed since listed)\n", 0},
+		{"file replaced by a remote directory deleted", map[string]bool{"f": true}, false, false, "/buckets/b/f (delete)\n/buckets/b/f (skip, created since listed)\n", 1},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			stub := stubFilerSvc{lookupErr: filer_pb.ErrNotFound}
+			if tc.kept {
+				stub = stubFilerSvc{lookupResp: &filer_pb.LookupDirectoryEntryResponse{Entry: listed}}
+			}
+			fake := &deleteRecordingFiler{
+				takenNameFiler: takenNameFiler{stubFilerSvc: stub},
+				listing:        map[string][]*filer_pb.Entry{"/buckets/b": {listed}},
+			}
+			remote := &listingRemote{dirs: map[string]map[string]bool{"/": tc.remote}}
+			var out strings.Builder
+			loc := &remote_pb.RemoteStorageLocation{Name: "r", Bucket: "rb", Path: "/"}
+			if err := pullMetadataDirectory(context.Background(), fake, &out, remote, util.FullPath("/buckets/b"), loc, tc.deleteStale, false); err != nil {
+				t.Fatalf("sync: %v", err)
+			}
+			if out.String() != tc.want || len(fake.creates) != tc.creates {
+				t.Fatalf("output %q with %d creates, want %q with %d", out.String(), len(fake.creates), tc.want, tc.creates)
+			}
+		})
+	}
+}

weed/shell/command_remote_mount.go

@@ -212,7 +212,11 @@ func ensureMountDirectory(commandEnv *CommandEnv, dir string, nonEmpty bool, rem
 // if an entry has synchronized metadata but has new updates
 //
 //	entry.Attributes.Mtime * 1,000,000,000    > entry.RemoteEntry.LastLocalSyncTsNs
-func doSaveRemoteEntry(client filer_pb.SeaweedFilerClient, localDir string, existingEntry *filer_pb.Entry, remoteEntry *filer_pb.RemoteEntry) error {
+//
+// The entry is written only while the filer still holds existingEntry; stale
+// reports that it changed since it was read and nothing was written.
+func doSaveRemoteEntry(client filer_pb.SeaweedFilerClient, localDir string, existingEntry *filer_pb.Entry, remoteEntry *filer_pb.RemoteEntry) (stale bool, err error) {
+	readEntry := proto.Clone(existingEntry).(*filer_pb.Entry)
 	existingEntry.RemoteEntry = remoteEntry
 	existingEntry.Attributes.FileSize = uint64(remoteEntry.RemoteSize)
 	existingEntry.Attributes.Mtime = remoteEntry.RemoteMtime
@@ -221,12 +225,5 @@ func doSaveRemoteEntry(client filer_pb.SeaweedFilerClient, localDir string, exis
 	existingEntry.Extended = filer.MergeRemoteContentEncoding(remoteEntry, existingEntry.Extended)
 	existingEntry.Chunks = nil
 	existingEntry.Content = nil
-	_, updateErr := client.UpdateEntry(context.Background(), &filer_pb.UpdateEntryRequest{
-		Directory: localDir,
-		Entry:     existingEntry,
-	})
-	if updateErr != nil {
-		return updateErr
-	}
-	return nil
+	return updateEntryIfUnchanged(context.Background(), client, localDir, existingEntry, readEntry)
 }

weed/shell/command_remote_uncache.go

@@ -12,6 +12,7 @@ import (
 	"github.com/seaweedfs/seaweedfs/weed/filer"
 	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
 	"github.com/seaweedfs/seaweedfs/weed/util"
+	"google.golang.org/protobuf/proto"
 )
 
 func init() {
@@ -106,18 +107,18 @@ func (c *commandRemoteUncache) uncacheContentData(commandEnv *CommandEnv, writer
 			return true // should not uncache an entry that is not synchronized with remote
 		}
 
-		entry.RemoteEntry.LastLocalSyncTsNs = 0
-		entry.Chunks = nil
-
 		fmt.Fprintf(writer, "Uncache %+v ... ", dir.Child(entry.Name))
 
+		var stale bool
 		err := commandEnv.WithFilerClient(false, func(client filer_pb.SeaweedFilerClient) error {
-			_, updateErr := client.UpdateEntry(context.Background(), &filer_pb.UpdateEntryRequest{
-				Directory: string(dir),
-				Entry:     entry,
-			})
+			var updateErr error
+			stale, updateErr = uncacheEntry(client, string(dir), entry)
 			return updateErr
 		})
+		if stale {
+			fmt.Fprintf(writer, "skipped, changed since it was read\n")
+			return true
+		}
 		if err != nil {
 			fmt.Fprintf(writer, "uncache %+v: %v\n", dir.Child(entry.Name), err)
 			return false
@@ -128,6 +129,15 @@ func (c *commandRemoteUncache) uncacheContentData(commandEnv *CommandEnv, writer
 	})
 }
 
+// uncacheEntry drops the local copy of entry only while the filer still holds
+// it as read, so a write that landed after the read keeps its data.
+func uncacheEntry(client filer_pb.SeaweedFilerClient, dir string, entry *filer_pb.Entry) (stale bool, err error) {
+	readEntry := proto.Clone(entry).(*filer_pb.Entry)
+	entry.RemoteEntry.LastLocalSyncTsNs = 0
+	entry.Chunks = nil
+	return updateEntryIfUnchanged(context.Background(), client, dir, entry, readEntry)
+}
+
 type FileFilter struct {
 	include     *string
 	exclude     *string

weed/shell/command_remote_uncache_test.go

@@ -5,6 +5,9 @@ import (
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/proto"
 )
 
 func TestFileFilter_matches_minCacheAge(t *testing.T) {
@@ -102,3 +105,39 @@ func TestFileFilter_matches_minCacheAge(t *testing.T) {
 		})
 	}
 }
+
+// The uncache clears the chunks of the entry its walk read. Conditioning the
+// write on that copy keeps a file overwritten since the walk from being reset
+// to the remote pointer with its new chunks dropped.
+func TestUncacheEntryIsConditionedOnTheReadEntry(t *testing.T) {
+	read := &filer_pb.Entry{
+		Name:        "f",
+		Chunks:      []*filer_pb.FileChunk{{Fid: &filer_pb.FileId{VolumeId: 3, FileKey: 1, Cookie: 7}}},
+		RemoteEntry: &filer_pb.RemoteEntry{StorageName: "r", LastLocalSyncTsNs: 5},
+	}
+	for _, tc := range []struct {
+		name  string
+		err   error
+		stale bool
+	}{
+		{"unchanged", nil, false},
+		{"overwritten since the walk", status.Error(codes.FailedPrecondition, "precondition failed"), true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			fake := &conditionalUpdateFiler{err: tc.err}
+			entry := proto.Clone(read).(*filer_pb.Entry)
+			stale, err := uncacheEntry(fake, "/buckets/b", entry)
+			if stale != tc.stale || (err != nil) != (tc.err != nil) {
+				t.Fatalf("stale=%v err=%v, want stale=%v err=%v", stale, err, tc.stale, tc.err)
+			}
+			clauses := fake.req.GetCondition().GetClauses()
+			if len(clauses) != 1 || clauses[0].Kind != filer_pb.WriteCondition_IF_ENTRY_EQUAL || !proto.Equal(clauses[0].ExpectedEntry, read) {
+				t.Fatalf("condition %v must expect the entry as read", fake.req.GetCondition())
+			}
+			written := fake.req.Entry
+			if len(written.Chunks) != 0 || written.RemoteEntry.LastLocalSyncTsNs != 0 {
+				t.Fatalf("written entry %v must drop the local copy", written)
+			}
+		})
+	}
+}