5 files changed, 72 insertions, 1 deletions
diff --git a/pkg/sentry/fs/fsutil/BUILD b/pkg/sentry/fs/fsutil/BUILD
index 01098675d..44f43b965 100644
--- a/pkg/sentry/fs/fsutil/BUILD
+++ b/pkg/sentry/fs/fsutil/BUILD
@@ -113,5 +113,6 @@ go_test(
         "//pkg/sentry/memmap",
         "//pkg/sentry/safemem",
         "//pkg/sentry/usermem",
+        "//pkg/syserror",
     ],
 )
diff --git a/pkg/sentry/fs/fsutil/host_mappable.go b/pkg/sentry/fs/fsutil/host_mappable.go
index 28686f3b3..ad0518b8f 100644
--- a/pkg/sentry/fs/fsutil/host_mappable.go
+++ b/pkg/sentry/fs/fsutil/host_mappable.go
@@ -149,7 +149,7 @@ func (h *HostMappable) Truncate(ctx context.Context, newSize int64) error {
 	}
 
 	// Invalidate COW mappings that may exist beyond the new size in case the file
-	// is being shrunk. Other mappinsg don't need to be invalidated because
+	// is being shrunk. Other mappings don't need to be invalidated because
 	// translate will just return identical mappings after invalidation anyway,
 	// and SIGBUS will be raised and handled when the mappings are touched.
 	//
@@ -167,6 +167,14 @@ func (h *HostMappable) Truncate(ctx context.Context, newSize int64) error {
 	return nil
 }
 
+// Allocate reserves space in the backing file.
+func (h *HostMappable) Allocate(ctx context.Context, offset int64, length int64) error {
+	h.truncateMu.RLock()
+	err := h.backingFile.Allocate(ctx, offset, length)
+	h.truncateMu.RUnlock()
+	return err
+}
+
 // Write writes to the file backing this mappable.
 func (h *HostMappable) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
 	h.truncateMu.RLock()
diff --git a/pkg/sentry/fs/fsutil/inode.go b/pkg/sentry/fs/fsutil/inode.go
index b6366d906..151be1d0d 100644
--- a/pkg/sentry/fs/fsutil/inode.go
+++ b/pkg/sentry/fs/fsutil/inode.go
@@ -34,6 +34,7 @@ type SimpleFileInode struct {
 	InodeNoExtendedAttributes `state:"nosave"`
 	InodeNoopRelease          `state:"nosave"`
 	InodeNoopWriteOut         `state:"nosave"`
+	InodeNotAllocatable       `state:"nosave"`
 	InodeNotDirectory         `state:"nosave"`
 	InodeNotMappable          `state:"nosave"`
 	InodeNotOpenable          `state:"nosave"`
@@ -61,6 +62,7 @@ type NoReadWriteFileInode struct {
 	InodeNoExtendedAttributes `state:"nosave"`
 	InodeNoopRelease          `state:"nosave"`
 	InodeNoopWriteOut         `state:"nosave"`
+	InodeNotAllocatable       `state:"nosave"`
 	InodeNotDirectory         `state:"nosave"`
 	InodeNotMappable          `state:"nosave"`
 	InodeNotSocket            `state:"nosave"`
@@ -465,3 +467,26 @@ func (InodeDenyWriteChecker) Check(ctx context.Context, inode *fs.Inode, p fs.Pe
 	}
 	return fs.ContextCanAccessFile(ctx, inode, p)
 }
+
+//InodeNotAllocatable can be used by Inodes that do not support Allocate().
+type InodeNotAllocatable struct{}
+
+func (InodeNotAllocatable) Allocate(_ context.Context, _ *fs.Inode, _, _ int64) error {
+	return syserror.EOPNOTSUPP
+}
+
+// InodeNoopAllocate implements fs.InodeOperations.Allocate as a noop.
+type InodeNoopAllocate struct{}
+
+// Allocate implements fs.InodeOperations.Allocate.
+func (InodeNoopAllocate) Allocate(_ context.Context, _ *fs.Inode, _, _ int64) error {
+	return nil
+}
+
+// InodeIsDirAllocate implements fs.InodeOperations.Allocate for directories.
+type InodeIsDirAllocate struct{}
+
+// Allocate implements fs.InodeOperations.Allocate.
+func (InodeIsDirAllocate) Allocate(_ context.Context, _ *fs.Inode, _, _ int64) error {
+	return syserror.EISDIR
+}
diff --git a/pkg/sentry/fs/fsutil/inode_cached.go b/pkg/sentry/fs/fsutil/inode_cached.go
index 76644e69d..03cad37f3 100644
--- a/pkg/sentry/fs/fsutil/inode_cached.go
+++ b/pkg/sentry/fs/fsutil/inode_cached.go
@@ -135,6 +135,10 @@ type CachedFileObject interface {
 	// the file was opened.
 	SetMaskedAttributes(ctx context.Context, mask fs.AttrMask, attr fs.UnstableAttr) error
 
+	// Allocate allows the caller to reserve disk space for the inode.
+	// It's equivalent to fallocate(2) with 'mode=0'.
+	Allocate(ctx context.Context, offset int64, length int64) error
+
 	// Sync instructs the remote filesystem to sync the file to stable storage.
 	Sync(ctx context.Context) error
 
@@ -336,6 +340,30 @@ func (c *CachingInodeOperations) Truncate(ctx context.Context, inode *fs.Inode,
 	return nil
 }
 
+// Allocate implements fs.InodeOperations.Allocate.
+func (c *CachingInodeOperations) Allocate(ctx context.Context, offset, length int64) error {
+	newSize := offset + length
+
+	// c.attr.Size is protected by both c.attrMu and c.dataMu.
+	c.attrMu.Lock()
+	defer c.attrMu.Unlock()
+	c.dataMu.Lock()
+	defer c.dataMu.Unlock()
+
+	if newSize <= c.attr.Size {
+		return nil
+	}
+
+	now := ktime.NowFromContext(ctx)
+	if err := c.backingFile.Allocate(ctx, offset, length); err != nil {
+		return err
+	}
+
+	c.attr.Size = newSize
+	c.touchModificationTimeLocked(now)
+	return nil
+}
+
 // WriteOut implements fs.InodeOperations.WriteOut.
 func (c *CachingInodeOperations) WriteOut(ctx context.Context, inode *fs.Inode) error {
 	c.attrMu.Lock()
diff --git a/pkg/sentry/fs/fsutil/inode_cached_test.go b/pkg/sentry/fs/fsutil/inode_cached_test.go
index 3f10efc12..be3d4b6fc 100644
--- a/pkg/sentry/fs/fsutil/inode_cached_test.go
+++ b/pkg/sentry/fs/fsutil/inode_cached_test.go
@@ -26,6 +26,7 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/sentry/memmap"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
 )
 
 type noopBackingFile struct{}
@@ -50,6 +51,10 @@ func (noopBackingFile) FD() int {
 	return -1
 }
 
+func (noopBackingFile) Allocate(ctx context.Context, offset int64, length int64) error {
+	return nil
+}
+
 func TestSetPermissions(t *testing.T) {
 	ctx := contexttest.Context(t)
 
@@ -237,6 +242,10 @@ func (*sliceBackingFile) FD() int {
 	return -1
 }
 
+func (f *sliceBackingFile) Allocate(ctx context.Context, offset int64, length int64) error {
+	return syserror.EOPNOTSUPP
+}
+
 type noopMappingSpace struct{}
 
 // Invalidate implements memmap.MappingSpace.Invalidate.