This is a joint topic proposal with Vivek Goyal.
Discuss remaining issues related to exporting a filesystem from host to
guest (see virtio-fs prototype posting[1] for more background):
* How to provide strong coherency guarantees?
- Fsnotify synchronous post op notification
- Extend lease (delegation) API to userspace
- Multi-component path revalidation
* Issues related to c/m/atime handling:
- Clock synchronization between host and guest (not an fs issue, but fs
has to deal with lack of it)
- Could we have O_NOCMTIME open flag?
* Shared access to file data:
- Use DAX in guest to access host page cache (mmap/munmap sections of
file in guest address space; happens dynamically on a need basis); is
this design reasonable?
- Avoids memory copies and cache duplication, but host page table setup
may have high cost. Can that be improved? (E.g. fault-ahead)
- Too many VMA’s on host per qemu instance?
* File locking:
- Host API for POSIX lock sharing?
* Ideas for the future:
- Buffering directory operations (e.g. "tar xfz ..." with as few
synchronous ops as possible)
[1] https://lore.kernel.org/lkml/20181210171318.16998-1-vgoyal@xxxxxxxxxx/
