Hard links Support Phase 1: Gofer Client dentry/inode refactor

[copybara-service]

Hard links Support Phase 1: Gofer Client dentry/inode refactor

• Decoupled dentry and inode: Cleanly separated dentry fields from the
  file's actual metadata (permissions, size, etc.), now residing in the inode.
• Dentry now holds inode pointer: The dentry struct embeds a pointer to
  the shared inode, reflecting the many-to-one relationship of hard links.
• impl logic moved to inode: The backend-specific logic (LISA FS
  vs. Direct FS) is no longer part of the dentry struct. Instead, the
  inode struct
  is extended to handle these implementations.
• Refactored Gofer client fs: Updated the Gofer client filesystem logic
  to work with the new dentry -> inode pointer structure.
• Renamed files: dentry_impl.go becomes inode_impl.go, and
  {directfs/lisafs}_dentry.go are now {directfs/lisafs}_inode.go to match the
  new design.
• Disabled Save/Restore in link::IsSameFile: Disabled save/restore in
  this specific check due to complexities in maintaining inode consistency
  across save/restore cycles. See comment in link.cc:45 for details.
• New Link Tests:
  • HardLinkChangeMode: Verifies hard link behavior, including mode changes
    across save/restore.

[Copilot]

Pull Request Overview

This PR implements Phase 1 of hard links support by refactoring the Gofer client’s dentry/inode code. Key changes include decoupling dentry fields from the file metadata by embedding an inode pointer into the dentry structure, updating various filesystem operations to use the new inode pointer, and modifying tests and build files accordingly.

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/util/test_util.cc	Renamed and reorganized functions to separate permissions from link count retrieval.
pkg/sentry/fsimpl/gofer/time.go	Updated time-related operations to use the new d.inode.fs references.
pkg/sentry/fsimpl/gofer/lisafs_dentry.go	Updated inode creation and error handling for Lisafs dentries.
pkg/sentry/fsimpl/gofer/filesystem.go	Refactored file operations to use d.inode references for notifications and locking.
pkg/sentry/fsimpl/gofer/directfs_dentry.go	Adjusted direct filesystem dentry operations to work with the embedded inode.

Comments suppressed due to low confidence (1)

test/util/test_util.cc:186

• The new function 'Permissions' returns the file's mode while 'Links' returns the link count. Consider adding inline documentation or renaming one of the functions to clearly differentiate their purposes.

PosixErrorOr<uint64_t> Permissions(const std::string& path) {

[Copilot]

Ensure that the shift from using 'd.fs' to 'd.inode.fs' in time functions is clearly documented to help future maintainers understand the new data flow.

[Copilot]

Add inline comments or enhance error handling to explain the scenario when createOrFindInodeStatx returns nil, ensuring that failure cases are clearly understood.

[Copilot]

Review all notification calls to confirm they consistently use 'd.inode.watches' throughout file operations for clarity and maintainability.

Suggested change

	parent.inode.watches.Notify(ctx, name, uint32(ev), 0, vfs.InodeEvent, false /* unlinked */)
	d.inode.watches.Notify(ctx, name, uint32(ev), 0, vfs.InodeEvent, false /* unlinked */)

[Copilot]

When createOrFindInodeStat returns nil, ensure that proper error handling is in place to prevent potential nil pointer dereferences.

Suggested change

	log.Warningf("could not create or find inode")
	if err == nil {
	err = fmt.Errorf("createOrFindInodeStat returned nil inode without error for inoKey: %v", inoKey)
	}
	log.Warningf("could not create or find inode: %v", err)

[avagin]

@tranji-cloud you can ignore all copilot comments. I added it just to check how useful it is.