Factor out the code to create / release a struct vboxsf_handle into
2 new helper functions.

This is a preparation patch for adding atomic_open support.

Fixes: 0fd16957 ("fs: Add VirtualBox guest shared folder (vboxsf) support")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

vboxsf_init_inode() is used both for initial setup of inode and for metadata
updates.  Tell it whether we are updating a live inode or setting up a new
instance and have it refuse to change type in the former case.

[fixed the braino caught by Hans de Goede <hdegoede@redhat.com>]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Extend some inode methods with an additional user namespace argument. A
filesystem that is aware of idmapped mounts will receive the user
namespace the mount has been marked with. This can be used for
additional permission checking and also to enable filesystems to
translate between uids and gids if they need to. We have implemented all
relevant helpers in earlier patches.

As requested we simply extend the exisiting inode method instead of
introducing new ones. This is a little more code churn but it's mostly
mechanical and doesnt't leave us with additional inode methods.

Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com


Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

VirtualBox hosts can share folders with guests, this commit adds a
VFS driver implementing the Linux-guest side of this, allowing folders
exported by the host to be mounted under Linux.

This driver depends on the guest <-> host IPC functions exported by
the vboxguest driver.

Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>