linux-kernel - Re: [PATCH 2/2] fat (exportfs): reconnect file handles to evicted inodes/dentries

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Date:	Sat, 07 Jul 2012 15:03:04 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	"Steven J. Magnani" <steve@...idescorp.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fat (exportfs): reconnect file handles to evicted inodes/dentries

"Steven J. Magnani" <steve@...idescorp.com> writes:

> On Sat, 2012-07-07 at 06:07 +0900, OGAWA Hirofumi wrote: 
>> "Steven J. Magnani" <steve@...idescorp.com> writes:
>> 
>> > On Wed, 2012-07-04 at 20:07 +0900, OGAWA Hirofumi wrote: 
>> >> Please don't add new lock_super() usage if it is not necessary. Almost
>> >> all of lock_super() just replaced lock_kernel() usage. It rather should
>> >> be removed in future.  Probably, this should use inode->i_mutex instead.
>> >> 
>> >> BTW, the above issue is same with all of directory read.
>> >
>> > I don't think there's really an alternative here. The cases addressed by
>> > this patch all involve walking on-disk structures via
>> > unofficial/temporary inodes created from information in the NFS handle
>> > (i.e., outside the normal inode creation paths). When this process is
>> > successful we end up with "official" connected inodes/dentries, but
>> > getting there is really a "bottom up" strategy instead of the usual "top
>> > down" approach.
>> >
>> > Because the "bottom up" method is lacking guarantees that "top down"
>> > takes for granted - i.e., that a cluster on disk that's supposed to be a
>> > directory actually *is* a directory -  I am adding some defensive code
>> > in the next spin of the patch.
>> 
>> I'm not sure what you meant. Where is the problem? ->get_name()? If so,
>> it has parent dentry parameter. What is the wrong if we take
>> mutex_lock(parent->d_inode)?
>
> The temporary/"unofficial" inodes are unhashed and thus not visible
> outside of the functions using them. They exist only to support access
> to directory contents when we can't gain that access via other means
> (because we only have "bottom up" information, about an object and
> perhaps its parent, in a form that can't be used to look up hashed
> inodes/dentries). Hashing them wouldn't help, because they don't have
> the correct key (for instance, in the case of a ".." entry).
>
> Am I missing something?

You mean the unhashed inode is created by ->get_parent()? If so, the
root cause sounds like ->get_parent() itself. If not, I'm not
understanding the meaning of the temporary/unofficial inode here.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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