[vbox-dev] Shared folder automount only mounts volumes as root on Linux

[Sérgio Basto]

On Thu, 2021-01-14 at 11:12 -0600, Larry Finger wrote:
> On 1/13/21 11:59 AM, Brent Paulson wrote:
> > This sounds like a mismatch between the VirtualBox-supplied mount
> > utilities and the Linux-supplied shared folder kernel module.  The
> > VirtualBox mount.vboxsf utility and the VBoxService automount
> > utility
> > both call mount(2) with a 'data' argument containing a
> > 'vbsf_mount_info_new' structure filled in with the mount
> > details.  The
> > VirtualBox shared folders kernel module knows how to parse this
> > structure but if the VirtualBox mount.vboxsf utility is used with a
> > Linux shared folder kernel module on a recent Linux kernel then the
> > fs_context_operations parse_monolithic function will be called
> > which on
> > Linux is currently:
> > 
> > static int vboxsf_parse_monolithic(struct fs_context *fc, void
> > *data)
> > {
> >      unsigned char *options = data;
> > 
> >      if (options && options[0] == VBSF_MOUNT_SIGNATURE_BYTE_0 &&
> >                 options[1] == VBSF_MOUNT_SIGNATURE_BYTE_1 &&
> >                 options[2] == VBSF_MOUNT_SIGNATURE_BYTE_2 &&
> >                 options[3] == VBSF_MOUNT_SIGNATURE_BYTE_3) {
> >          vbg_err("vboxsf: Old binary mount data not supported,
> > remove obsolete mount.vboxsf and/or update your VBoxService.\n");
> >          return -EINVAL;
> >      }
> > 
> >      return generic_parse_monolithic(fc, data);
> > }
> > 
> > The 'vbsf_mount_info_new' structure contains the identifying
> > signature
> > bytes referenced above which explains why the mount options such as
> > uid=123 aren't seen when there is a userland vs. kernel mismatch.
> > 
> > The VirtualBox mount utilities are going to start calling mount(2)
> > with a
> > 'data' argument containing a string of comma-separated mount
> > options in
> > the not-too-distant future so that any mismatch going forward won't
> > cause such surprises.
> 
> Brent,
> 
> Thanks for the update. I look forward to the not-too-distant update.

I tested with kernel 5.10.7-200.fc33.x86_64 in host and in guest , and
no problem . 

> Larry
> 
-- 
Sérgio M. B.