svn commit: r252435 - in head/sys/ufs: ffs ufs

[Xin Li]

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On 6/30/13 8:00 PM, Pedro F. Giffuni wrote:
> Author: pfg Date: Mon Jul  1 03:00:15 2013 New Revision: 252435 
> URL: http://svnweb.freebsd.org/changeset/base/252435
> 
> Log: Change i_gen in UFS to an unsigned type.
> 
[...]
> Modified: head/sys/ufs/ffs/ffs_vfsops.c 
> ==============================================================================
>
> 
- --- head/sys/ufs/ffs/ffs_vfsops.c	Mon Jul  1 02:48:27 2013	(r252434)
> +++ head/sys/ufs/ffs/ffs_vfsops.c	Mon Jul  1 03:00:15 2013
> (r252435) @@ -1791,7 +1791,7 @@ ffs_vgetf(mp, ino, flags, vpp,
> ffs_flags * already have one. This should only happen on old
> filesystems. */ if (ip->i_gen == 0) { -		ip->i_gen = arc4random() /
> 2 + 1; +		ip->i_gen = arc4random() + 1; if ((vp->v_mount->mnt_flag
> & MNT_RDONLY) == 0) { ip->i_flag |= IN_MODIFIED; DIP_SET(ip, i_gen,
> ip->i_gen);
> 

Why ip->i_gen must be non-zero here?  (I think it does not.  Note that
arc4random() can return UINT32_MAX so the new code does not guarantee
this anyway, while old code does).

If my understanding of the code is right, I think it doesn't really
hurt to have 0 in ip->i_gen in the places where arc4random() is used
(next time it would be regenerated), so probably we can just use
ip->i_gen = arc4random()?

However, if I was wrong, you probably want some construction like this:

%%%	for (;;) {
%%%		ip->i_gen = arc4random();
%%%		if (ip->i_gen != UINT32_MAX)
%%%			break;
%%%	}
%%%	ip->i_gen++;

Or we probably need to import a variant of arc4random_uniform into kernel?

Cheers,
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