Re: devvp->v_specmountpoint

[David Holland <dholland-tech%netbsd.org@localhost>]

On Mon, Oct 27, 2008 at 05:02:02PM +0100, Reinoud Zandijk wrote:
 > i'm puzzled by the apparent requirement to set the v_specmountpoint of the 
 > device a FS is mounted on to the mountpoint on mount. All fs's seem to 
 > follow it but its function is not clear.

It seems to be mostly used for accounting and for putting fs-specific
hacks in places they shouldn't be. However, it's used in some other
places in ways I wouldn't be quick to dismiss, like fscow_run() and
reassignbuf().

That, and, of course, making sure each block device is used only
once.

 > Isn't the vp->v_specmountpoint provided so that if a vnode is describing a 
 > VBLK, the mounted FS can be looked up and/or fsynced too? (Wont this fsync 
 > the mounted root vnode only ?)

That logic also seems to exist. It looks as if it does the right
thing.

 > Since NilFS can have multiple mounts on the same device the 
 > v_specmountpoint is at best ambiguous if not inadequate.

Erm, what does that mean, and how does it interact with mount and
fstab? E.g. what's supposed to happen if I mount half a dozen of these
from /dev/wd0h and then do "umount /dev/wd0h"?

It seems like a can of worms much larger than just the mount point
reference.

 > Should I just keep v_specmountpoint NULL for this FS and will that break 
 > anything?

I can't say I'd recommend it.

-- 
David A. Holland
dholland%netbsd.org@localhost