Re: [RFC PATCH v1 1/7] fs: Add inode_get_ino() and implement get_ino() for NFS

Burn Alting
2024-10-14T08:40:39Z

On 13/10/24 21:17, Jeff Layton wrote:
> On Fri, 2024-10-11 at 17:30 +0200, Mickaël Salaün wrote:
>> On Fri, Oct 11, 2024 at 07:39:33AM -0700, Christoph Hellwig wrote:
>>> On Fri, Oct 11, 2024 at 03:52:42PM +0200, Mickaël Salaün wrote:
>>>>>> Yes, but how do you call getattr() without a path?
>>>>>
>>>>> You don't because inode numbers are irrelevant without the path.
>>>>
>>>> They are for kernel messages and audit logs. Please take a look at the
>>>> use cases with the other patches.
>>>
>>> It still is useless. E.g. btrfs has duplicate inode numbers due to
>>> subvolumes.
>>
>> At least it reflects what users see.
>>
>>>
>>> If you want a better pretty but not useful value just work on making
>>> i_ino 64-bits wide, which is long overdue.
>>
>> That would require too much work for me, and this would be a pain to
>> backport to all stable kernels.
>>
>
> Would it though? Adding this new inode operation seems sub-optimal.
>
> Inode numbers are static information. Once an inode number is set on an
> inode it basically never changes. This patchset will turn all of those
> direct inode->i_ino fetches into a pointer chase for the new inode
> operation, which will then almost always just result in a direct fetch.
>
> A better solution here would be to make inode->i_ino a u64, and just
> fix up all of the places that touch it to expect that. Then, just
> ensure that all of the filesystems set it properly when instantiating
> new inodes. Even on 32-bit arch, you likely wouldn't need a seqcount
> loop or anything to fetch this since the chance of a torn read there is
> basically zero.
>
> If there are places where we need to convert i_ino down to 32-bits,
> then we can just use some scheme like nfs_fattr_to_ino_t(), or just
> cast i_ino to a u32.
>
> Yes, it'd be a larger patchset, but that seems like it would be a
> better solution.
As someone who lives in the analytical user space of Linux audit, I
take it that for large (say >200TB) file systems, the inode value
reported in audit PATH records is no longer forensically defensible and
it's use as a correlation item is of questionable value now?