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authorFabricio Voznika <fvoznika@google.com>2021-04-20 11:47:28 -0700
committergVisor bot <gvisor-bot@google.com>2021-04-20 11:48:48 -0700
commitbf1e14cf8a24100fd12292a87e4fc3a439399669 (patch)
tree27fb92b2f070da4efd4ae0b455cf2091ccee8b07 /pkg/sentry/fsimpl/gofer
parent3fff4c4a0fbb1b132348d4b82f61cc38a4cc6cb2 (diff)
Speed up O_APPEND with remote revalidating
Remote revalidating requires to update file size on every write on a file opened with O_APPEND. If host FD exists, it can be used to update the size and skip round trip to the gofer. With this change, O_APPEND writes with remote revalidating is almost as fast as exclusive mode: BM_Append VFS1 60.7us VFS2 56.8us VFS2 exclusive 14.2us This change 15.8us Updates #1792 PiperOrigin-RevId: 369486801
Diffstat (limited to 'pkg/sentry/fsimpl/gofer')
-rw-r--r--pkg/sentry/fsimpl/gofer/gofer.go57
-rw-r--r--pkg/sentry/fsimpl/gofer/regular_file.go9
2 files changed, 47 insertions, 19 deletions
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 966f01698..f491aa641 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -987,36 +987,63 @@ func (d *dentry) updateFromP9AttrsLocked(mask p9.AttrMask, attr *p9.Attr) {
}
// Preconditions: !d.isSynthetic().
+// Preconditions: d.metadataMu is locked.
+func (d *dentry) refreshSizeLocked(ctx context.Context) error {
+ d.handleMu.RLock()
+
+ if d.writeFD < 0 {
+ d.handleMu.RUnlock()
+ // Ask the gofer if we don't have a host FD.
+ return d.updateFromGetattrLocked(ctx)
+ }
+
+ var stat unix.Statx_t
+ err := unix.Statx(int(d.writeFD), "", unix.AT_EMPTY_PATH, unix.STATX_SIZE, &stat)
+ d.handleMu.RUnlock() // must be released before updateSizeLocked()
+ if err != nil {
+ return err
+ }
+ d.updateSizeLocked(stat.Size)
+ return nil
+}
+
+// Preconditions: !d.isSynthetic().
func (d *dentry) updateFromGetattr(ctx context.Context) error {
- // Use d.readFile or d.writeFile, which represent 9P fids that have been
+ // d.metadataMu must be locked *before* we getAttr so that we do not end up
+ // updating stale attributes in d.updateFromP9AttrsLocked().
+ d.metadataMu.Lock()
+ defer d.metadataMu.Unlock()
+ return d.updateFromGetattrLocked(ctx)
+}
+
+// Preconditions:
+// * !d.isSynthetic().
+// * d.metadataMu is locked.
+func (d *dentry) updateFromGetattrLocked(ctx context.Context) error {
+ // Use d.readFile or d.writeFile, which represent 9P FIDs that have been
// opened, in preference to d.file, which represents a 9P fid that has not.
// This may be significantly more efficient in some implementations. Prefer
// d.writeFile over d.readFile since some filesystem implementations may
// update a writable handle's metadata after writes to that handle, without
// making metadata updates immediately visible to read-only handles
// representing the same file.
- var (
- file p9file
- handleMuRLocked bool
- )
- // d.metadataMu must be locked *before* we getAttr so that we do not end up
- // updating stale attributes in d.updateFromP9AttrsLocked().
- d.metadataMu.Lock()
- defer d.metadataMu.Unlock()
d.handleMu.RLock()
- if !d.writeFile.isNil() {
+ handleMuRLocked := true
+ var file p9file
+ switch {
+ case !d.writeFile.isNil():
file = d.writeFile
- handleMuRLocked = true
- } else if !d.readFile.isNil() {
+ case !d.readFile.isNil():
file = d.readFile
- handleMuRLocked = true
- } else {
+ default:
file = d.file
d.handleMu.RUnlock()
+ handleMuRLocked = false
}
+
_, attrMask, attr, err := file.getAttr(ctx, dentryAttrMask())
if handleMuRLocked {
- d.handleMu.RUnlock()
+ d.handleMu.RUnlock() // must be released before updateFromP9AttrsLocked()
}
if err != nil {
return err
diff --git a/pkg/sentry/fsimpl/gofer/regular_file.go b/pkg/sentry/fsimpl/gofer/regular_file.go
index 713f0a480..f0e7bbaf7 100644
--- a/pkg/sentry/fsimpl/gofer/regular_file.go
+++ b/pkg/sentry/fsimpl/gofer/regular_file.go
@@ -204,18 +204,19 @@ func (fd *regularFileFD) pwrite(ctx context.Context, src usermem.IOSequence, off
}
d := fd.dentry()
+
+ d.metadataMu.Lock()
+ defer d.metadataMu.Unlock()
+
// If the fd was opened with O_APPEND, make sure the file size is updated.
// There is a possible race here if size is modified externally after
// metadata cache is updated.
if fd.vfsfd.StatusFlags()&linux.O_APPEND != 0 && !d.cachedMetadataAuthoritative() {
- if err := d.updateFromGetattr(ctx); err != nil {
+ if err := d.refreshSizeLocked(ctx); err != nil {
return 0, offset, err
}
}
- d.metadataMu.Lock()
- defer d.metadataMu.Unlock()
-
// Set offset to file size if the fd was opened with O_APPEND.
if fd.vfsfd.StatusFlags()&linux.O_APPEND != 0 {
// Holding d.metadataMu is sufficient for reading d.size.