How to safely access inode/dentry obtained from struct page *?

[Pranay Srivastava]

On 01-Sep-2014 10:18 AM, "Pranay Srivastava" <pranjas at gmail.com> wrote:
>
>
> On 30-Aug-2014 10:49 AM, "Joshi" <joshiiitr at gmail.com> wrote:
> >
> > I am trying to obtain file name at block layer level (above IO
scheduler).
> > At this level I receive bio structure, within which page pointers are
kept.
> >
> > Thereby I do following to obtain the inode and dentry -
> >
> > struct inode *inode_ptr = page->mapping->host;
> > if (inode_ptr != NULL)
> > /* Access dentry i.e. i_dentry in the inode */
> >
>
> Are you doing this in readpage(s) or writepage(s) callback? If that's the
case your page would be locked and dentry/inode wouldn't go away.
>
> If you are doing something else then first make sure you do lock_page and
proceed only if you get that page lock.
>
> Second you can try dget and dput before you start working with dentry.
>
> >
> > This works usually. But problem is, inode and dentry may get released
> > from inode and dentry cache at any time.
> > While accessing inode/dentry I need to ensure that till the time I am
> > accessing'em these structure remain valid in memory.
> > Is it possible to ensure that? Which structures/locks I need to check
> > for the purpose.
>
> is this your observation from your test case? Can you explain your test
case a bit.
>
Have you seen d_alias and see if that can help you with filename?
> >
> > Appreciate any help.
> >
> > Thanks!
> >
> > --
> > Joshi
> >
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