From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 24CAE2E11A6; Thu, 19 Mar 2026 01:30:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773883842; cv=none; b=pMCFIgS30zjsGbFfsWdPfm5Wt51jgQI87/k1jHqOj/GNSJiH2Ib1QMSruvOpKTYtKRMhwgCv9fGDDsYL2Hxy4zjFuLJczUd9SJ89dTpcCSMPJNV1dt+uyjS1ZSb9abA7ZGfgG6Z8n89Q3+aVsBtLYE51WCptEhdaOe7mgkX3xFs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773883842; c=relaxed/simple; bh=mu7F6EbKH3FQO2cw+iEfmXw0RIlWeJ7w3ZCalUplYig=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=bjimHQlIO93VmhJLvlifcvCJ3PNZYW0wSwnpErceH3LgZ5IDEhbs/Ah2sfcK9U/CXHcZsEtzH5hgeoT0KvLQvhGG6aWn6z+Slqo52U69f+fc2zeqluKisEcHggQmzpD2jxRyU3tTjv0F9qk8xOSOq8mviCHYWvjzmzCzhR4iapI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=groves.net; spf=pass smtp.mailfrom=groves.net; arc=none smtp.client-ip=216.40.44.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=groves.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=groves.net Received: from omf09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 53E7D1B72E8; Thu, 19 Mar 2026 01:30:34 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: john@groves.net) by omf09.hostedemail.com (Postfix) with ESMTPA id EE64E2002A; Thu, 19 Mar 2026 01:30:23 +0000 (UTC) From: John Groves To: John Groves , Miklos Szeredi , Dan Williams , Bernd Schubert , Alison Schofield Cc: John Groves , Jonathan Corbet , Shuah Khan , Vishal Verma , Dave Jiang , Matthew Wilcox , Jan Kara , Alexander Viro , David Hildenbrand , Christian Brauner , "Darrick J . Wong" , Randy Dunlap , Jeff Layton , Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Bagas Sanjaya , Chen Linxuan , James Morse , Fuad Tabba , Sean Christopherson , Shivank Garg , Ackerley Tng , Gregory Price , Aravind Ramesh , Ajay Joshi , venkataravis@micron.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, John Groves Subject: [PATCH V8 7/8] dax: Add fs_dax_get() func to prepare dax for fs-dax usage Date: Wed, 18 Mar 2026 20:30:22 -0500 Message-ID: <20260319013022.4531-1-john@groves.net> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260318202737.4344.dax@groves.net> References: <20260318202737.4344.dax@groves.net> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: EE64E2002A X-Stat-Signature: gigd84f1a8scdd4pjso1om9e5abp3egz X-Rspamd-Server: rspamout03 X-Session-Marker: 6A6F686E4067726F7665732E6E6574 X-Session-ID: U2FsdGVkX18W7ZaX2fgubPZ7Q2KPHmP9OrS/mINysaU= X-HE-Tag: 1773883823-871223 X-HE-Meta: U2FsdGVkX19W1sakYRyevFB0WDJ857L+jtQD1a7ycQIGNV3ki62iK9SuRsfk/96KSoJ+U8xsPYGumJkQ+y+6LYcun+5u/nM1/AUdQqonakPdkJNYYoPr5nlew62r92JjU4mGXj9ka3hLCAzHu5N1X8HLmTIjMXknTgCuEiMDfHoMllNVjpJfg7SyPcJoEk5crffZTqyjwK63Swyuz0aPuk3wqMVnyNP2OlH83joyGT+O4jczRZ+wfDPfVZU2Cfqm93QLzcCNBTIXlyCZ7tH0t/0ombLUIWeO3QDBVt2fktG2VhmLS9q4urfDSMz7LLDCBRCx6kV6pC0= The fs_dax_get() function should be called by fs-dax file systems after opening a fsdev dax device. This adds holder_operations, which provides a memory failure callback path and effects exclusivity between callers of fs_dax_get(). fs_dax_get() is specific to fsdev_dax, so it checks the driver type (which required touching bus.[ch]). fs_dax_get() fails if fsdev_dax is not bound to the memory. This function serves the same role as fs_dax_get_by_bdev(), which dax file systems call after opening the pmem block device. This can't be located in fsdev.c because struct dax_device is opaque there. This will be called by fs/fuse/famfs.c in a subsequent commit. Signed-off-by: John Groves --- drivers/dax/bus.c | 2 -- drivers/dax/bus.h | 2 ++ drivers/dax/super.c | 66 ++++++++++++++++++++++++++++++++++++++++++++- include/linux/dax.h | 16 ++++++++--- 4 files changed, 79 insertions(+), 7 deletions(-) diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c index 562e2b06f61a..8a8710a8234e 100644 --- a/drivers/dax/bus.c +++ b/drivers/dax/bus.c @@ -39,8 +39,6 @@ static int dax_bus_uevent(const struct device *dev, struct kobj_uevent_env *env) return add_uevent_var(env, "MODALIAS=" DAX_DEVICE_MODALIAS_FMT, 0); } -#define to_dax_drv(__drv) container_of_const(__drv, struct dax_device_driver, drv) - static struct dax_id *__dax_match_id(const struct dax_device_driver *dax_drv, const char *dev_name) { diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h index 880bdf7e72d7..dc6f112ac4a4 100644 --- a/drivers/dax/bus.h +++ b/drivers/dax/bus.h @@ -42,6 +42,8 @@ struct dax_device_driver { void (*remove)(struct dev_dax *dev); }; +#define to_dax_drv(__drv) container_of_const(__drv, struct dax_device_driver, drv) + int __dax_driver_register(struct dax_device_driver *dax_drv, struct module *module, const char *mod_name); #define dax_driver_register(driver) \ diff --git a/drivers/dax/super.c b/drivers/dax/super.c index ba0b4cd18a77..d4ab60c406bf 100644 --- a/drivers/dax/super.c +++ b/drivers/dax/super.c @@ -14,6 +14,7 @@ #include #include #include "dax-private.h" +#include "bus.h" /** * struct dax_device - anchor object for dax services @@ -111,6 +112,10 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev, u64 *start_off, } EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev); +#endif /* CONFIG_BLOCK && CONFIG_FS_DAX */ + +#if IS_ENABLED(CONFIG_FS_DAX) + void fs_put_dax(struct dax_device *dax_dev, void *holder) { if (dax_dev && holder && @@ -119,7 +124,66 @@ void fs_put_dax(struct dax_device *dax_dev, void *holder) put_dax(dax_dev); } EXPORT_SYMBOL_GPL(fs_put_dax); -#endif /* CONFIG_BLOCK && CONFIG_FS_DAX */ + +/** + * fs_dax_get() - get ownership of a devdax via holder/holder_ops + * + * fs-dax file systems call this function to prepare to use a devdax device for + * fsdax. This is like fs_dax_get_by_bdev(), but the caller already has struct + * 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) +{ + struct dev_dax *dev_dax; + struct dax_device_driver *dax_drv; + int id; + + id = dax_read_lock(); + if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode)) { + dax_read_unlock(id); + return -ENODEV; + } + dax_read_unlock(id); + + /* Verify the device is bound to fsdev_dax driver */ + dev_dax = dax_get_private(dax_dev); + if (!dev_dax) { + iput(&dax_dev->inode); + return -ENODEV; + } + + device_lock(&dev_dax->dev); + if (!dev_dax->dev.driver) { + device_unlock(&dev_dax->dev); + iput(&dax_dev->inode); + return -ENODEV; + } + dax_drv = to_dax_drv(dev_dax->dev.driver); + if (dax_drv->type != DAXDRV_FSDEV_TYPE) { + device_unlock(&dev_dax->dev); + iput(&dax_dev->inode); + return -EOPNOTSUPP; + } + device_unlock(&dev_dax->dev); + + if (cmpxchg(&dax_dev->holder_data, NULL, holder)) { + iput(&dax_dev->inode); + return -EBUSY; + } + + dax_dev->holder_ops = hops; + + return 0; +} +EXPORT_SYMBOL_GPL(fs_dax_get); +#endif /* CONFIG_FS_DAX */ enum dax_device_flags { /* !alive + rcu grace period == no new operations / mappings */ diff --git a/include/linux/dax.h b/include/linux/dax.h index 8d469a23c485..f14fa2147175 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -131,7 +131,6 @@ int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk); void dax_remove_host(struct gendisk *disk); struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev, u64 *start_off, void *holder, const struct dax_holder_operations *ops); -void fs_put_dax(struct dax_device *dax_dev, void *holder); #else static inline int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk) { @@ -146,12 +145,12 @@ static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev, { return NULL; } -static inline void fs_put_dax(struct dax_device *dax_dev, void *holder) -{ -} #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */ #if IS_ENABLED(CONFIG_FS_DAX) +void fs_put_dax(struct dax_device *dax_dev, void *holder); +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); int dax_writeback_mapping_range(struct address_space *mapping, struct dax_device *dax_dev, struct writeback_control *wbc); @@ -166,6 +165,15 @@ dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, void dax_unlock_mapping_entry(struct address_space *mapping, unsigned long index, dax_entry_t cookie); #else +static inline void fs_put_dax(struct dax_device *dax_dev, void *holder) +{ +} + +static inline int fs_dax_get(struct dax_device *dax_dev, void *holder, + const struct dax_holder_operations *hops) +{ + return -EOPNOTSUPP; +} static inline struct page *dax_layout_busy_page(struct address_space *mapping) { return NULL; -- 2.53.0