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Message-ID: <20260107153332.64727-6-john@groves.net>
Date: Wed, 7 Jan 2026 09:33:14 -0600
From: John Groves <John@...ves.net>
To: John Groves <John@...ves.net>,
Miklos Szeredi <miklos@...redi.hu>,
Dan Williams <dan.j.williams@...el.com>,
Bernd Schubert <bschubert@....com>,
Alison Schofield <alison.schofield@...el.com>
Cc: John Groves <jgroves@...ron.com>,
Jonathan Corbet <corbet@....net>,
Vishal Verma <vishal.l.verma@...el.com>,
Dave Jiang <dave.jiang@...el.com>,
Matthew Wilcox <willy@...radead.org>,
Jan Kara <jack@...e.cz>,
Alexander Viro <viro@...iv.linux.org.uk>,
David Hildenbrand <david@...nel.org>,
Christian Brauner <brauner@...nel.org>,
"Darrick J . Wong" <djwong@...nel.org>,
Randy Dunlap <rdunlap@...radead.org>,
Jeff Layton <jlayton@...nel.org>,
Amir Goldstein <amir73il@...il.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Stefan Hajnoczi <shajnocz@...hat.com>,
Joanne Koong <joannelkoong@...il.com>,
Josef Bacik <josef@...icpanda.com>,
Bagas Sanjaya <bagasdotme@...il.com>,
Chen Linxuan <chenlinxuan@...ontech.com>,
James Morse <james.morse@....com>,
Fuad Tabba <tabba@...gle.com>,
Sean Christopherson <seanjc@...gle.com>,
Shivank Garg <shivankg@....com>,
Ackerley Tng <ackerleytng@...gle.com>,
Gregory Price <gourry@...rry.net>,
Aravind Ramesh <arramesh@...ron.com>,
Ajay Joshi <ajayjoshi@...ron.com>,
venkataravis@...ron.com,
linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org,
nvdimm@...ts.linux.dev,
linux-cxl@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
John Groves <john@...ves.net>
Subject: [PATCH V3 05/21] dax: Add dax_set_ops() for setting dax_operations at bind time
From: John Groves <John@...ves.net>
The dax_device is created (in the non-pmem case) at hmem probe time via
devm_create_dev_dax(), before we know which driver (device_dax,
fsdev_dax, or kmem) will bind - by calling alloc_dax() with NULL ops,
drivers (i.e. fsdev_dax) that need specific dax_operations must set
them later.
Add dax_set_ops() exported function so fsdev_dax can set its ops at
probe time and clear them on remove. device_dax doesn't need ops since
it uses the mmap fault path directly.
Use cmpxchg() to atomically set ops only if currently NULL, returning
-EBUSY if ops are already set. This prevents accidental double-binding.
Clearing ops (NULL) always succeeds.
Signed-off-by: John Groves <john@...ves.net>
---
drivers/dax/fsdev.c | 12 ++++++++++++
drivers/dax/super.c | 38 +++++++++++++++++++++++++++++++++++++-
include/linux/dax.h | 1 +
3 files changed, 50 insertions(+), 1 deletion(-)
diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c
index 9e2f83aa2584..3f4f593896e3 100644
--- a/drivers/dax/fsdev.c
+++ b/drivers/dax/fsdev.c
@@ -330,12 +330,24 @@ static int fsdev_dax_probe(struct dev_dax *dev_dax)
if (rc)
return rc;
+ /* Set the dax operations for fs-dax access path */
+ rc = dax_set_ops(dax_dev, &dev_dax_ops);
+ if (rc)
+ return rc;
+
run_dax(dax_dev);
return devm_add_action_or_reset(dev, fsdev_kill, dev_dax);
}
+static void fsdev_dax_remove(struct dev_dax *dev_dax)
+{
+ /* Clear ops on unbind so they aren't used with a different driver */
+ dax_set_ops(dev_dax->dax_dev, NULL);
+}
+
static struct dax_device_driver fsdev_dax_driver = {
.probe = fsdev_dax_probe,
+ .remove = fsdev_dax_remove,
.type = DAXDRV_FSDEV_TYPE,
};
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index c00b9dff4a06..ba0b4cd18a77 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -157,6 +157,9 @@ long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
if (!dax_alive(dax_dev))
return -ENXIO;
+ if (!dax_dev->ops)
+ return -EOPNOTSUPP;
+
if (nr_pages < 0)
return -EINVAL;
@@ -207,6 +210,10 @@ int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
if (!dax_alive(dax_dev))
return -ENXIO;
+
+ if (!dax_dev->ops)
+ return -EOPNOTSUPP;
+
/*
* There are no callers that want to zero more than one page as of now.
* Once users are there, this check can be removed after the
@@ -223,7 +230,7 @@ EXPORT_SYMBOL_GPL(dax_zero_page_range);
size_t dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff,
void *addr, size_t bytes, struct iov_iter *iter)
{
- if (!dax_dev->ops->recovery_write)
+ if (!dax_dev->ops || !dax_dev->ops->recovery_write)
return 0;
return dax_dev->ops->recovery_write(dax_dev, pgoff, addr, bytes, iter);
}
@@ -307,6 +314,35 @@ void set_dax_nomc(struct dax_device *dax_dev)
}
EXPORT_SYMBOL_GPL(set_dax_nomc);
+/**
+ * dax_set_ops - set the dax_operations for a dax_device
+ * @dax_dev: the dax_device to configure
+ * @ops: the operations to set (may be NULL to clear)
+ *
+ * This allows drivers to set the dax_operations after the dax_device
+ * has been allocated. This is needed when the device is created before
+ * the driver that needs specific ops is bound (e.g., fsdev_dax binding
+ * to a dev_dax created by hmem).
+ *
+ * When setting non-NULL ops, fails if ops are already set (returns -EBUSY).
+ * When clearing ops (NULL), always succeeds.
+ *
+ * Return: 0 on success, -EBUSY if ops already set
+ */
+int dax_set_ops(struct dax_device *dax_dev, const struct dax_operations *ops)
+{
+ if (ops) {
+ /* Setting ops: fail if already set */
+ if (cmpxchg(&dax_dev->ops, NULL, ops) != NULL)
+ return -EBUSY;
+ } else {
+ /* Clearing ops: always allowed */
+ dax_dev->ops = NULL;
+ }
+ return 0;
+}
+EXPORT_SYMBOL_GPL(dax_set_ops);
+
bool dax_alive(struct dax_device *dax_dev)
{
lockdep_assert_held(&dax_srcu);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 74e098010016..3fcd8562b72b 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -246,6 +246,7 @@ static inline void dax_break_layout_final(struct inode *inode)
bool dax_alive(struct dax_device *dax_dev);
void *dax_get_private(struct dax_device *dax_dev);
+int dax_set_ops(struct dax_device *dax_dev, const struct dax_operations *ops);
long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
enum dax_access_mode mode, void **kaddr, unsigned long *pfn);
size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
--
2.49.0
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