Better interop for NFS/SMB file share mode/reservation

[Jeremy Allison]

On Fri, Feb 08, 2019 at 10:02:43PM +0200, Amir Goldstein via samba-technical 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.
> 
> But if samba can't figure out a way to keep a single open file
> descriptor for oplocks per client-file, then this model doesn't
> help us make any progress.

Samba uses a single file descriptor per SMB2 open file
handle. Is this what you meant ? We need this to keep
the per-handle OFD locks around.