VIRTIO_IOC_EXPORT_FD_REQ behavior when exporting the same FD multiple times

[valpackett]

libkrun/src/devices/src/virtio/fs/linux/passthrough.rs

Line 2225 in 44312fd

exports.insert((self.cfg.export_fsid, handle), fd);

I just noticed that the VIRTIO_IOC_EXPORT_FD_REQ handler always writes new FDs to the export table without checking whether an entry already existed. So the previous entry is dropped there and replaced with a new one if the same handle is exported twice. This is probably fine?? but it probably would be better to reuse the fd?

[slp]

It may be worth trying to reuse it to avoid the dup() syscall, which is pretty expensive.