Re: Your CVS fix 1.109 to union_vnops.c

takawata_at_jp.freebsd.org wrote:
> In message <4160ED06.6070603_at_geminix.org>, Uwe Doering wrote:
> 
>>Takanori Watanabe wrote:
>>[...]
>>>Ok, the issue Uwe says is when underlying filesystem and 
>>>wrapping filesystem are diffent and if there are two files
>>>with same identifier exists. 
>>>And the issue I want to fix is when underlying filesystem and
>>>wrapping filesystem are same so getcwd routine failed to distinguish 
>>>the mount point.
>>>
>>>So it can be solved by translating fsid if the fsid of a file is same as
>>>that of mountpoint. True?
>>
>>Correct.  In this case the inode number is guaranteed to be unique. 
>>This might be okay as a local patch, but it is IMHO not a fix suited for 
>>FreeBSD in general.
> 
> Ok. How about this?
> 
> Index: union_vnops.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/fs/unionfs/union_vnops.c,v
> retrieving revision 1.109
> diff -u -r1.109 union_vnops.c
> --- union_vnops.c	2 Oct 2004 17:17:04 -0000	1.109
> +++ union_vnops.c	4 Oct 2004 07:04:38 -0000
> _at__at_ -951,6 +951,8 _at__at_
>  		error = VOP_GETATTR(vp, vap, ap->a_cred, ap->a_td);
>  		if (error)
>  			return (error);
> +		ap->a_vap->va_fsid = ap->a_vp->v_mount->mnt_stat.f_fsid.val[0];
> +
>  		/* XXX isn't this dangerous without a lock? */
>  		union_newsize(ap->a_vp, vap->va_size, VNOVAL);
>  	}
> _at__at_ -972,7 +974,6 _at__at_
>  		union_newsize(ap->a_vp, VNOVAL, vap->va_size);
>  	}
>  
> -	ap->a_vap->va_fsid = ap->a_vp->v_mount->mnt_stat.f_fsid.val[0];
>  
>  	if ((vap != ap->a_vap) && (vap->va_type == VDIR))
>  		ap->a_vap->va_nlink += vap->va_nlink;

This wouldn't be correct, either.  Unionfs can be stacked, that is, you 
can't even be sure for a single layer that the passed up va_fsid will 
always be the same.  The underlying unionfs can be comprised of two 
layers on two different file systems as well, and so on.  You can 
override va_fsid only if the original file system id is guaranteed to be 
the same for all files in that layer (single file system case).

    Uwe
-- 
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