On Wed, Jan 5, 2022 at 10:12 AM Darrick J. Wong <djwong@xxxxxxxxxx> wrote:
>
> On Sun, Dec 26, 2021 at 10:34:31PM +0800, Shiyang Ruan wrote:
> > To easily track filesystem from a pmem device, we introduce a holder for
> > dax_device structure, and also its operation. This holder is used to
> > remember who is using this dax_device:
> > - When it is the backend of a filesystem, the holder will be the
> > instance of this filesystem.
> > - When this pmem device is one of the targets in a mapped device, the
> > holder will be this mapped device. In this case, the mapped device
> > has its own dax_device and it will follow the first rule. So that we
> > can finally track to the filesystem we needed.
> >
> > The holder and holder_ops will be set when filesystem is being mounted,
> > or an target device is being activated.
> >
> > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> > ---
> > drivers/dax/super.c | 62 +++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/dax.h | 29 +++++++++++++++++++++
> > 2 files changed, 91 insertions(+)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index c46f56e33d40..94c51f2ee133 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -20,15 +20,20 @@
> > * @inode: core vfs
> > * @cdev: optional character interface for "device dax"
> > * @private: dax driver private data
> > + * @holder_data: holder of a dax_device: could be filesystem or mapped device
> > * @flags: state and boolean properties
> > + * @ops: operations for dax_device
> > + * @holder_ops: operations for the inner holder
> > */
> > struct dax_device {
> > struct inode inode;
> > struct cdev cdev;
> > void *private;
> > struct percpu_rw_semaphore rwsem;
> > + void *holder_data;
> > unsigned long flags;
> > const struct dax_operations *ops;
> > + const struct dax_holder_operations *holder_ops;
> > };
> >
> > static dev_t dax_devt;
> > @@ -192,6 +197,29 @@ int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
> > }
> > EXPORT_SYMBOL_GPL(dax_zero_page_range);
> >
> > +int dax_holder_notify_failure(struct dax_device *dax_dev, u64 off,
> > + u64 len, int mf_flags)
> > +{
> > + int rc;
> > +
> > + dax_read_lock(dax_dev);
> > + if (!dax_alive(dax_dev)) {
> > + rc = -ENXIO;
> > + goto out;
> > + }
> > +
> > + if (!dax_dev->holder_ops) {
> > + rc = -EOPNOTSUPP;
> > + goto out;
> > + }
> > +
> > + rc = dax_dev->holder_ops->notify_failure(dax_dev, off, len, mf_flags);
> > +out:
> > + dax_read_unlock(dax_dev);
> > + return rc;
> > +}
> > +EXPORT_SYMBOL_GPL(dax_holder_notify_failure);
> > +
> > #ifdef CONFIG_ARCH_HAS_PMEM_API
> > void arch_wb_cache_pmem(void *addr, size_t size);
> > void dax_flush(struct dax_device *dax_dev, void *addr, size_t size)
> > @@ -254,6 +282,10 @@ void kill_dax(struct dax_device *dax_dev)
> > return;
> > dax_write_lock(dax_dev);
> > clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
> > +
> > + /* clear holder data */
> > + dax_dev->holder_ops = NULL;
> > + dax_dev->holder_data = NULL;
> > dax_write_unlock(dax_dev);
> > }
> > EXPORT_SYMBOL_GPL(kill_dax);
> > @@ -401,6 +433,36 @@ void put_dax(struct dax_device *dax_dev)
> > }
> > EXPORT_SYMBOL_GPL(put_dax);
> >
> > +void dax_register_holder(struct dax_device *dax_dev, void *holder,
> > + const struct dax_holder_operations *ops)
> > +{
> > + if (!dax_alive(dax_dev))
> > + return;
> > +
> > + dax_dev->holder_data = holder;
> > + dax_dev->holder_ops = ops;
>
> Shouldn't this return an error code if the dax device is dead or if
> someone already registered a holder? I'm pretty sure XFS should not
> bind to a dax device if someone else already registered for it...
Agree, yes.
>
> ...unless you want to use a notifier chain for failure events so that
> there can be multiple consumers of dax failure events?
No, I would hope not. It should be 1:1 holders to dax-devices. Similar
ownership semantics like bd_prepare_to_claim().
