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Wong" , Randy Dunlap , Jeff Layton , Kent Overstreet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Aravind Ramesh , Ajay Joshi , John Groves Subject: [RFC V2 02/18] dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage Date: Thu, 3 Jul 2025 13:50:16 -0500 Message-Id: <20250703185032.46568-3-john@groves.net> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20250703185032.46568-1-john@groves.net> References: <20250703185032.46568-1-john@groves.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This function should be called by fs-dax file systems after opening the devdax device. This adds holder_operations, which effects exclusivity between callers of fs_dax_get(). This function serves the same role as fs_dax_get_by_bdev(), which dax file systems call after opening the pmem block device. This also adds the CONFIG_DEV_DAX_IOMAP Kconfig parameter Signed-off-by: John Groves --- drivers/dax/Kconfig | 6 ++++++ drivers/dax/super.c | 30 ++++++++++++++++++++++++++++++ include/linux/dax.h | 5 +++++ 3 files changed, 41 insertions(+) diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig index d656e4c0eb84..ad19fa966b8b 100644 --- a/drivers/dax/Kconfig +++ b/drivers/dax/Kconfig @@ -78,4 +78,10 @@ config DEV_DAX_KMEM =20 Say N if unsure. =20 +config DEV_DAX_IOMAP + depends on DEV_DAX && DAX + def_bool y + help + Support iomap mapping of devdax devices (for FS-DAX file + systems that reside on character /dev/dax devices) endif diff --git a/drivers/dax/super.c b/drivers/dax/super.c index e16d1d40d773..48bab9b5f341 100644 --- a/drivers/dax/super.c +++ b/drivers/dax/super.c @@ -122,6 +122,36 @@ void fs_put_dax(struct dax_device *dax_dev, void *hold= er) EXPORT_SYMBOL_GPL(fs_put_dax); #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */ =20 +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP) +/** + * fs_dax_get() + * + * fs-dax file systems call this function to prepare to use a devdax devic= e for + * fsdax. This is like fs_dax_get_by_bdev(), but the caller already has st= ruct + * dev_dax (and there * is no bdev). The holder makes this exclusive. + * + * @dax_dev: dev to be prepared for fs-dax usage + * @holder: filesystem or mapped device inside the dax_device + * @hops: operations for the inner holder + * + * Returns: 0 on success, <0 on failure + */ +int fs_dax_get(struct dax_device *dax_dev, void *holder, + const struct dax_holder_operations *hops) +{ + if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode)) + return -ENODEV; + + if (cmpxchg(&dax_dev->holder_data, NULL, holder)) + return -EBUSY; + + dax_dev->holder_ops =3D hops; + + return 0; +} +EXPORT_SYMBOL_GPL(fs_dax_get); +#endif /* DEV_DAX_IOMAP */ + enum dax_device_flags { /* !alive + rcu grace period =3D=3D no new operations / mappings */ DAXDEV_ALIVE, diff --git a/include/linux/dax.h b/include/linux/dax.h index df41a0017b31..86bf5922f1b0 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -51,6 +51,11 @@ struct dax_holder_operations { =20 #if IS_ENABLED(CONFIG_DAX) struct dax_device *alloc_dax(void *private, const struct dax_operations *o= ps); + +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP) +int fs_dax_get(struct dax_device *dax_dev, void *holder, const struct dax_= holder_operations *hops); +struct dax_device *inode_dax(struct inode *inode); +#endif void *dax_holder(struct dax_device *dax_dev); void put_dax(struct dax_device *dax_dev); void kill_dax(struct dax_device *dax_dev); --=20 2.49.0