Implement setattr+clunk in 9P

This is to cover the common pattern: open->read/write->close,
where SetAttr needs to be called to update atime/mtime before
the file is closed.

Benchmark results:

BM_OpenReadClose/10240 CPU
setattr+clunk: 63783 ns
VFS2:          68109 ns
VFS1:          72507 ns

Updates #1198

PiperOrigin-RevId: 329628461

2 files changed, 30 insertions, 17 deletions

diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 57bff1789..73d9e772d 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -1300,30 +1300,36 @@ func (d *dentry) destroyLocked(ctx context.Context) {
 	d.handleMu.Unlock()
 
 	if !d.file.isNil() {
+		valid := p9.SetAttrMask{}
+		attr := p9.SetAttr{}
 		if !d.isDeleted() {
 			// Write dirty timestamps back to the remote filesystem.
-			atimeDirty := atomic.LoadUint32(&d.atimeDirty) != 0
-			mtimeDirty := atomic.LoadUint32(&d.mtimeDirty) != 0
-			if atimeDirty || mtimeDirty {
+			if atomic.LoadUint32(&d.atimeDirty) != 0 {
+				valid.ATime = true
+				valid.ATimeNotSystemTime = true
 				atime := atomic.LoadInt64(&d.atime)
+				attr.ATimeSeconds = uint64(atime / 1e9)
+				attr.ATimeNanoSeconds = uint64(atime % 1e9)
+			}
+			if atomic.LoadUint32(&d.mtimeDirty) != 0 {
+				valid.MTime = true
+				valid.MTimeNotSystemTime = true
 				mtime := atomic.LoadInt64(&d.mtime)
-				if err := d.file.setAttr(ctx, p9.SetAttrMask{
-					ATime:              atimeDirty,
-					ATimeNotSystemTime: atimeDirty,
-					MTime:              mtimeDirty,
-					MTimeNotSystemTime: mtimeDirty,
-				}, p9.SetAttr{
-					ATimeSeconds:     uint64(atime / 1e9),
-					ATimeNanoSeconds: uint64(atime % 1e9),
-					MTimeSeconds:     uint64(mtime / 1e9),
-					MTimeNanoSeconds: uint64(mtime % 1e9),
-				}); err != nil {
-					log.Warningf("gofer.dentry.destroyLocked: failed to write dirty timestamps back: %v", err)
-				}
+				attr.MTimeSeconds = uint64(mtime / 1e9)
+				attr.MTimeNanoSeconds = uint64(mtime % 1e9)
+			}
+		}
+
+		// Check if attributes need to be changed before closing the file.
+		if valid.ATime || valid.MTime {
+			if err := d.file.setAttrClose(ctx, valid, attr); err != nil {
+				log.Warningf("gofer.dentry.destroyLocked: failed to close file with write dirty timestamps: %v", err)
 			}
+		} else if err := d.file.close(ctx); err != nil {
+			log.Warningf("gofer.dentry.destroyLocked: failed to close file: %v", err)
 		}
-		d.file.close(ctx)
 		d.file = p9file{}
+
 		// Remove d from the set of syncable dentries.
 		d.fs.syncMu.Lock()
 		delete(d.fs.syncableDentries, d)
diff --git a/pkg/sentry/fsimpl/gofer/p9file.go b/pkg/sentry/fsimpl/gofer/p9file.go
index 87f0b877f..21b4a96fe 100644
--- a/pkg/sentry/fsimpl/gofer/p9file.go
+++ b/pkg/sentry/fsimpl/gofer/p9file.go
@@ -127,6 +127,13 @@ func (f p9file) close(ctx context.Context) error {
 	return err
 }
 
+func (f p9file) setAttrClose(ctx context.Context, valid p9.SetAttrMask, attr p9.SetAttr) error {
+	ctx.UninterruptibleSleepStart(false)
+	err := f.file.SetAttrClose(valid, attr)
+	ctx.UninterruptibleSleepFinish(false)
+	return err
+}
+
 func (f p9file) open(ctx context.Context, flags p9.OpenFlags) (*fd.FD, p9.QID, uint32, error) {
 	ctx.UninterruptibleSleepStart(false)
 	fdobj, qid, iounit, err := f.file.Open(flags)