Implement fallocate(2)

Closes #225

PiperOrigin-RevId: 247508791
Change-Id: I04f47cf2770b30043e5a272aba4ba6e11d0476cc

1 files changed, 28 insertions, 0 deletions

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()