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Message-ID: <CAPcyv4h3M9f1-C5e9kHTfPaRYR_zN4gzQWgR+ZyhNmG_SL-u+A@mail.gmail.com>
Date: Wed, 5 Jan 2022 11:20:12 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Shiyang Ruan <ruansy.fnst@...itsu.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-xfs <linux-xfs@...r.kernel.org>,
Linux NVDIMM <nvdimm@...ts.linux.dev>,
Linux MM <linux-mm@...ck.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
david <david@...morbit.com>,
Christoph Hellwig <hch@...radead.org>,
Jane Chu <jane.chu@...cle.com>
Subject: Re: [PATCH v9 02/10] dax: Introduce holder for dax_device
On Wed, Jan 5, 2022 at 10:56 AM Darrick J. Wong <djwong@...nel.org> wrote:
>
> On Wed, Jan 05, 2022 at 10:23:08AM -0800, Dan Williams wrote:
> > On Wed, Jan 5, 2022 at 10:12 AM Darrick J. Wong <djwong@...nel.org> 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@...itsu.com>
> > > > ---
> > > > 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().
>
> Does each partition on a pmem device still have its own dax_device?
No, it never did...
Just as before, each dax-device is still associated with a gendisk /
whole-block_device. The recent change is that instead of needing that
partition-block_device plumbed to convert a relative block number to
its absolute whole-block_device offset the filesystem now handles that
at iomap_begin() time. See:
if (mapping_flags & IOMAP_DAX)
iomap->addr += target->bt_dax_part_off;
...in xfs_bmbt_to_iomap() (in -next). I.e. bdev_dax_pgoff() is gone
with the lead-in reworks.
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