[Virtio-fs] [RFC] Using hard links instead of lo_inode->fd

[Vivek Goyal <vgoyal@redhat.com>]

Hi All,

Max has been trying to solve the problem of not having to keep an O_PATH
fd open for every file (until inode goes away). Lot of inodes can get
cached in guest inode cache and soon we can hit number of max fd limit.

Today Christophe de Dinechin mentioned that can we maintain hardlinks
for these files and open these hardlinks instead whenever we need
lo_inode->fd.

So say there is a notion of "workdir" which is passed to virtiofs where
virtiofsd can create hardlinks. Once inode comes into existence, we
create this link in workdir/<file-link>. Once last reference to inode
is dropped, workdir/<file-link> is removed.

Now any operation which needs the lo_inode->fd, can do operation on
workdir/<file-link>.

How does this proposal sound. What are the issues where. Some of the
which came to surface during discussion with david gilbert are.

1. links can't be created for directories. So this will only help with
  regular files. 

2. There might be a performance penalty. We don't know yet.

3. More overhead of managing workdir by the user/tools.


Anything else? Is this a viable idea even if we can implement only
for regular files.

Thanks
Vivek