4 files changed, 59 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/gofer/regular_file.go b/pkg/sentry/fsimpl/gofer/regular_file.go
index 404a452c4..faba73af2 100644
--- a/pkg/sentry/fsimpl/gofer/regular_file.go
+++ b/pkg/sentry/fsimpl/gofer/regular_file.go
@@ -24,6 +24,7 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/p9"
 	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
@@ -67,6 +68,34 @@ func (fd *regularFileFD) OnClose(ctx context.Context) error {
 	return d.handle.file.flush(ctx)
 }
 
+// Allocate implements vfs.FileDescriptionImpl.Allocate.
+func (fd *regularFileFD) Allocate(ctx context.Context, mode, offset, length uint64) error {
+
+	d := fd.dentry()
+	d.metadataMu.Lock()
+	defer d.metadataMu.Unlock()
+
+	size := offset + length
+
+	// Allocating a smaller size is a noop.
+	if size <= d.size {
+		return nil
+	}
+
+	d.handleMu.Lock()
+	defer d.handleMu.Unlock()
+
+	err := d.handle.file.allocate(ctx, p9.ToAllocateMode(mode), offset, length)
+	if err != nil {
+		return err
+	}
+	d.size = size
+	if !d.cachedMetadataAuthoritative() {
+		d.touchCMtimeLocked()
+	}
+	return nil
+}
+
 // PRead implements vfs.FileDescriptionImpl.PRead.
 func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
 	if offset < 0 {
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index d5e73ddae..007b3332e 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -543,6 +543,16 @@ func (f *fileDescription) Release() {
 	// noop
 }
 
+// Allocate implements vfs.FileDescriptionImpl.
+func (f *fileDescription) Allocate(ctx context.Context, mode, offset, length uint64) error {
+	if !f.inode.seekable {
+		return syserror.ESPIPE
+	}
+
+	// TODO(gvisor.dev/issue/2923): Implement Allocate for non-pipe hostfds.
+	return syserror.EOPNOTSUPP
+}
+
 // PRead implements FileDescriptionImpl.
 func (f *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
 	i := f.inode
diff --git a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
index 5f7853a2a..ca8b8c63b 100644
--- a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
@@ -236,6 +236,11 @@ func (fd *GenericDirectoryFD) SetStat(ctx context.Context, opts vfs.SetStatOptio
 	return inode.SetStat(ctx, fd.filesystem(), creds, opts)
 }
 
+// Allocate implements vfs.FileDescriptionImpl.Allocate.
+func (fd *GenericDirectoryFD) Allocate(ctx context.Context, mode, offset, length uint64) error {
+	return fd.DirectoryFileDescriptionDefaultImpl.Allocate(ctx, mode, offset, length)
+}
+
 // LockPOSIX implements vfs.FileDescriptionImpl.LockPOSIX.
 func (fd *GenericDirectoryFD) LockPOSIX(ctx context.Context, uid fslock.UniqueID, t fslock.LockType, start, length uint64, whence int16, block fslock.Blocker) error {
 	return fd.Locks().LockPOSIX(ctx, &fd.vfsfd, uid, t, start, length, whence, block)
diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file.go b/pkg/sentry/fsimpl/tmpfs/regular_file.go
index b805aadd0..6691add96 100644
--- a/pkg/sentry/fsimpl/tmpfs/regular_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file.go
@@ -274,6 +274,21 @@ func (fd *regularFileFD) Release() {
 	// noop
 }
 
+// Allocate implements vfs.FileDescriptionImpl.Allocate.
+func (fd *regularFileFD) Allocate(ctx context.Context, mode, offset, length uint64) error {
+	f := fd.inode().impl.(*regularFile)
+
+	f.inode.mu.Lock()
+	defer f.inode.mu.Unlock()
+	oldSize := f.size
+	size := offset + length
+	if oldSize >= size {
+		return nil
+	}
+	_, err := f.truncateLocked(size)
+	return err
+}
+
 // PRead implements vfs.FileDescriptionImpl.PRead.
 func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
 	if offset < 0 {