Re: [PATCH 1/1] do_truncate needs to increment iversion

[Kasatkin, Dmitry]

On Thu, Dec 15, 2011 at 11:55 PM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 14 Dec 2011 18:44:57 +0200
> Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx> wrote:
>
>> IMA/EVM uses iversion to identify if file content has been changed.
>> It has been found that when file is opened, truncated with ftruncate()
>> and then closed, iversion is not updated.
>>
>> This patch adds iversion incrementation to do_truncate().
>
> I confess that I've never really fully understood what i_version is
> supposed to do, so I'm not in any position to comment on where, when
> and why the thing should be updated.
>
> At present it gets updated in file_update_time() so I suppose that
> we're not calling file_update_time() in the ftruncate case, which
> sounds wrong?

What I see from notify_change(), it updates the time...
So what is really missing is incrimination of i_version...

>
> It's notable that file_update_time() will not update i_version if the
> inode has NOCMTIME. ÂThis might be wrong, but one would need to know
> the intent of i_version to be able to say. ÂDo your files have
> S_NOCMTIME set?

Yes. I saw it and even made a test to verify if is the reason for
i_version not to be updated...
But it was not set.
I have the same feeling that i_version should be updated despite NOCMTIME,
because i_version supposed to work if mounted with "iversion" option....
I think it should not have dependency to other mount options...

>
>> --- a/fs/open.c
>> +++ b/fs/open.c
>> @@ -56,6 +56,8 @@ int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
>> Â Â Â Â Â Â Â newattrs.ia_valid |= ret | ATTR_FORCE;
>>
>> Â Â Â mutex_lock(&dentry->d_inode->i_mutex);
>> + Â Â if (IS_I_VERSION(dentry->d_inode))
>> + Â Â Â Â Â Â inode_inc_iversion(dentry->d_inode);
>> Â Â Â ret = notify_change(dentry, &newattrs);
>> Â Â Â mutex_unlock(&dentry->d_inode->i_mutex);
>> Â Â Â return ret;
>
> With four evaluations, it is time to cache dentry->d_inode in a local.

True...

Thanks..
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