Better interop for NFS/SMB file share mode/reservation

[Amir Goldstein]

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.

Thanks,
Amir.