Add MultiGetAttr message to 9P

While using remote-validation, the vast majority of time spent during
FS operations is re-walking the path to check for modifications and
then closing the file given that in most cases it has not been
modified externally.

This change introduces a new 9P message called MultiGetAttr which bulks
query attributes of several files in one shot. The returned attributes are
then used to update cached dentries before they are walked. File attributes
are updated for files that still exist. Dentries that have been deleted are
removed from the cache. And negative cache entries are removed if a new
file/directory was created externally. Similarly, synthetic dentries are
replaced if a file/directory is created externally.

The bulk update needs to be carefull not to follow symlinks, cross mount
points, because the gofer doesn't know how to resolve symlinks and where
mounts points are located. It also doesn't walk to the parent ("..") to
avoid deadlocks.

Here are the results:

Workload        VFS1       VFS2     Change
bazel action     115s       70s	     28.8s
Stat/100      11,043us   7,623us      974us

Updates #1638

PiperOrigin-RevId: 369325957

1 files changed, 41 insertions, 41 deletions

diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 00f1847d8..8b392232a 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -208,11 +208,11 @@ func (vfs *VirtualFilesystem) AccessAt(ctx context.Context, creds *auth.Credenti
 	for {
 		err := rp.mount.fs.impl.AccessAt(ctx, rp, creds, ats)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -230,11 +230,11 @@ func (vfs *VirtualFilesystem) GetDentryAt(ctx context.Context, creds *auth.Crede
 				dentry: d,
 			}
 			rp.mount.IncRef()
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return vd, nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return VirtualDentry{}, err
 		}
 	}
@@ -252,7 +252,7 @@ func (vfs *VirtualFilesystem) getParentDirAndName(ctx context.Context, creds *au
 			}
 			rp.mount.IncRef()
 			name := rp.Component()
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return parentVD, name, nil
 		}
 		if checkInvariants {
@@ -261,7 +261,7 @@ func (vfs *VirtualFilesystem) getParentDirAndName(ctx context.Context, creds *au
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return VirtualDentry{}, "", err
 		}
 	}
@@ -292,7 +292,7 @@ func (vfs *VirtualFilesystem) LinkAt(ctx context.Context, creds *auth.Credential
 	for {
 		err := rp.mount.fs.impl.LinkAt(ctx, rp, oldVD)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			oldVD.DecRef(ctx)
 			return nil
 		}
@@ -302,7 +302,7 @@ func (vfs *VirtualFilesystem) LinkAt(ctx context.Context, creds *auth.Credential
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			oldVD.DecRef(ctx)
 			return err
 		}
@@ -331,7 +331,7 @@ func (vfs *VirtualFilesystem) MkdirAt(ctx context.Context, creds *auth.Credentia
 	for {
 		err := rp.mount.fs.impl.MkdirAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if checkInvariants {
@@ -340,7 +340,7 @@ func (vfs *VirtualFilesystem) MkdirAt(ctx context.Context, creds *auth.Credentia
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -366,7 +366,7 @@ func (vfs *VirtualFilesystem) MknodAt(ctx context.Context, creds *auth.Credentia
 	for {
 		err := rp.mount.fs.impl.MknodAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if checkInvariants {
@@ -375,7 +375,7 @@ func (vfs *VirtualFilesystem) MknodAt(ctx context.Context, creds *auth.Credentia
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -444,7 +444,7 @@ func (vfs *VirtualFilesystem) OpenAt(ctx context.Context, creds *auth.Credential
 	for {
 		fd, err := rp.mount.fs.impl.OpenAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 
 			if opts.FileExec {
 				if fd.Mount().Flags.NoExec {
@@ -468,7 +468,7 @@ func (vfs *VirtualFilesystem) OpenAt(ctx context.Context, creds *auth.Credential
 			return fd, nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil, err
 		}
 	}
@@ -480,11 +480,11 @@ func (vfs *VirtualFilesystem) ReadlinkAt(ctx context.Context, creds *auth.Creden
 	for {
 		target, err := rp.mount.fs.impl.ReadlinkAt(ctx, rp)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return target, nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return "", err
 		}
 	}
@@ -533,7 +533,7 @@ func (vfs *VirtualFilesystem) RenameAt(ctx context.Context, creds *auth.Credenti
 	for {
 		err := rp.mount.fs.impl.RenameAt(ctx, rp, oldParentVD, oldName, renameOpts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			oldParentVD.DecRef(ctx)
 			return nil
 		}
@@ -543,7 +543,7 @@ func (vfs *VirtualFilesystem) RenameAt(ctx context.Context, creds *auth.Credenti
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			oldParentVD.DecRef(ctx)
 			return err
 		}
@@ -569,7 +569,7 @@ func (vfs *VirtualFilesystem) RmdirAt(ctx context.Context, creds *auth.Credentia
 	for {
 		err := rp.mount.fs.impl.RmdirAt(ctx, rp)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if checkInvariants {
@@ -578,7 +578,7 @@ func (vfs *VirtualFilesystem) RmdirAt(ctx context.Context, creds *auth.Credentia
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -590,11 +590,11 @@ func (vfs *VirtualFilesystem) SetStatAt(ctx context.Context, creds *auth.Credent
 	for {
 		err := rp.mount.fs.impl.SetStatAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -606,11 +606,11 @@ func (vfs *VirtualFilesystem) StatAt(ctx context.Context, creds *auth.Credential
 	for {
 		stat, err := rp.mount.fs.impl.StatAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return stat, nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return linux.Statx{}, err
 		}
 	}
@@ -623,11 +623,11 @@ func (vfs *VirtualFilesystem) StatFSAt(ctx context.Context, creds *auth.Credenti
 	for {
 		statfs, err := rp.mount.fs.impl.StatFSAt(ctx, rp)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return statfs, nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return linux.Statfs{}, err
 		}
 	}
@@ -652,7 +652,7 @@ func (vfs *VirtualFilesystem) SymlinkAt(ctx context.Context, creds *auth.Credent
 	for {
 		err := rp.mount.fs.impl.SymlinkAt(ctx, rp, target)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if checkInvariants {
@@ -661,7 +661,7 @@ func (vfs *VirtualFilesystem) SymlinkAt(ctx context.Context, creds *auth.Credent
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -686,7 +686,7 @@ func (vfs *VirtualFilesystem) UnlinkAt(ctx context.Context, creds *auth.Credenti
 	for {
 		err := rp.mount.fs.impl.UnlinkAt(ctx, rp)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if checkInvariants {
@@ -695,7 +695,7 @@ func (vfs *VirtualFilesystem) UnlinkAt(ctx context.Context, creds *auth.Credenti
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -707,7 +707,7 @@ func (vfs *VirtualFilesystem) BoundEndpointAt(ctx context.Context, creds *auth.C
 	for {
 		bep, err := rp.mount.fs.impl.BoundEndpointAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return bep, nil
 		}
 		if checkInvariants {
@@ -716,7 +716,7 @@ func (vfs *VirtualFilesystem) BoundEndpointAt(ctx context.Context, creds *auth.C
 			}
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil, err
 		}
 	}
@@ -729,7 +729,7 @@ func (vfs *VirtualFilesystem) ListXattrAt(ctx context.Context, creds *auth.Crede
 	for {
 		names, err := rp.mount.fs.impl.ListXattrAt(ctx, rp, size)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return names, nil
 		}
 		if err == syserror.ENOTSUP {
@@ -737,11 +737,11 @@ func (vfs *VirtualFilesystem) ListXattrAt(ctx context.Context, creds *auth.Crede
 			// fs/xattr.c:vfs_listxattr() falls back to allowing the security
 			// subsystem to return security extended attributes, which by
 			// default don't exist.
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil, nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil, err
 		}
 	}
@@ -754,11 +754,11 @@ func (vfs *VirtualFilesystem) GetXattrAt(ctx context.Context, creds *auth.Creden
 	for {
 		val, err := rp.mount.fs.impl.GetXattrAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return val, nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return "", err
 		}
 	}
@@ -771,11 +771,11 @@ func (vfs *VirtualFilesystem) SetXattrAt(ctx context.Context, creds *auth.Creden
 	for {
 		err := rp.mount.fs.impl.SetXattrAt(ctx, rp, *opts)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}
@@ -787,11 +787,11 @@ func (vfs *VirtualFilesystem) RemoveXattrAt(ctx context.Context, creds *auth.Cre
 	for {
 		err := rp.mount.fs.impl.RemoveXattrAt(ctx, rp, name)
 		if err == nil {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return nil
 		}
 		if !rp.handleError(ctx, err) {
-			vfs.putResolvingPath(ctx, rp)
+			rp.Release(ctx)
 			return err
 		}
 	}