Approval request of some additions to src/sys/kern/vfs_subr.c and src/sys/sys/vnode.h

[Daichi GOTO]

Kostik Belousov wrote:
> On Fri, Apr 25, 2008 at 07:21:20PM +0900, Daichi GOTO wrote:
>> Hi Konstantin :)
>>
>> To fix a unionfs issue of http://www.freebsd.org/cgi/query-pr.cgi?pr=109377,
>> we need to add new functions
>>
>>    void vkernrele(struct vnode *vp);
>>    void vkernref(struct vnode *vp);
>>
>> and one value
>>
>>    int	v_kernusecount; /* i ref count of kernel */
>>
>> to src/sys/sys/vnode.h and rc/sys/kern/vfs_subr.c.
>>
>> Unionfs will be panic when lower fs layer is forced umounted by
>> "umount -f".  So to avoid this issue, we've added
>> "v_kernusecount" value that means "a vnode count that kernel are
>> using".  vkernrele() and vkernref() are functions that manage
>> "v_kernusecount" value.
>>
>> Please check those and give us an approve or some comments!
> 
> There is already the vnode reference count. From your description, I cannot
> understand how the kernusecount would prevent the panic when forced unmount
> is performed. Could you, please, show the actual code ? PR mentioned
> does not contain any patch.

Oops, sorry. patch is follow:
   http://people.freebsd.org/~daichi/unionfs/experiments/unionfs-p20-3.diff

> The problem you described is common for the kernel code, and right way
> to handle it, for now, is to keep refcount _and_ check for the forced
> reclaim.

-- 
   Daichi GOTO, http://people.freebsd.org/~daichi