Better interop for NFS/SMB file share mode/reservation

[Amir Goldstein]

On Fri, Feb 8, 2019 at 10:17 PM J. Bruce Fields <bfields at fieldses.org> wrote:
>
> On Fri, Feb 08, 2019 at 10:02:43PM +0200, Amir Goldstein wrote:
> > On Fri, Feb 8, 2019 at 5:51 PM J. Bruce Fields <bfields at fieldses.org> wrote:
> > >
> > > On Fri, Feb 08, 2019 at 04:45:46PM +0200, Amir Goldstein wrote:
> > > > - check_conflicting_open() is changed to use inode_is_open_for_read()
> > > >   instead of checking d_count and i_count.
> > >
> > > Independently of the rest, I'd love to do away with those
> > > d_count/i_count checks.  What's inode_is_open_for_read()?
> > >
> >
> > It would look maybe something like this:
> >
> > static inline bool file_is_open_for_read(const struct inode *file)
> > {
> >         struct inode *inode = file_inode(file);
> >         int countself = (file->f_mode & (FMODE_READ | FMODE_WRITE)) ==
> > FMODE_READ) ? 1 : 0;
> >
> >         return atomic_read(&inode->i_readcount) > countself;
> > }
> >
> > And it would allow for acquiring F_WRLCK lease if other
> > instances of inode are open O_PATH.
> > A slight change of semantics that seems harmless(?)
> > and will allow some flexibility.
>
> How did I not know about i_readcount?  (Looking)  I guess it would mean
> adding some dependence on CONFIG_IMA, hm.
>

Yes, or we remove ifdef CONFIG_IMA from i_readcount.
I am not sure if the concern was size of struct inode
(shouldn't increase on 64bit arch) or the accounting on
open/close. The impact doesn't look significant (?)..

Thanks,
Amir.