From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.7]) (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 770602D3ECF; Thu, 19 Feb 2026 16:07:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771517280; cv=none; b=lgGz85G+xG6l2SU/EBQjR255kEJRrFcY5qyE6bUq4S9cpQv4SAfquUAf/taF8WMIjRi7KaGQWI45K0rIIsnCG0Pp3WmQZxeJ3Il+k3v15yazv2/Cm/KXODxV0OKt4857PFkM+SjR6bP1Pg65YjZUP/Lh0aBFcQo5sB8g6nNB/sw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771517280; c=relaxed/simple; bh=zlPqV4I0bErDRfP8a/M2jtQm4fY10/MZ0I7ZNyxtfzg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uo1GKCW+l9P8ur+GVxxCDLl2DAEdDgB7tVHsfmMx39p9PhAsmi0OBb3p6puQqMrkTfe64CuD0KVcJ2gaTumlf644wGobuuWColowpZ3qLhivLRyc7vjpK4odNpbfKCipaG+8FBppDknrGnU+jAjshyq6qXa1AhzSxnML+SK1CYA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=b0UhgStd; arc=none smtp.client-ip=192.198.163.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="b0UhgStd" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1771517278; x=1803053278; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=zlPqV4I0bErDRfP8a/M2jtQm4fY10/MZ0I7ZNyxtfzg=; b=b0UhgStdinbLr+68Fa9ktWEZNy33u9hrnFavFlelZBDP27Hm7qQlX4VQ VVWLjiEh5XsLh+hi92Kxm0RSiYkosSPCNyem2jL7e0D3a+YWrXj7UhRbW MhlQl8mVxblEGtLpmDpFnYEt0LBA+1jMri9g6VtacVWLFkK6p7G0Pzk5k vQyXk5UYRoSQfsq1Ea1wyGVAth390OD8MYkT3wqjxeCIj7fLpH2+plnn+ 9N60WIdrnxl8E3g1xc23uy1bYhj7o6NbTVC5EtJgGmPqgqap49/SCzxdc yumiCS55aSlZnrKp5AmG+Tvz/fs/eREGMWfh09+MUdHk3LNoktZlPf2bV w==; X-CSE-ConnectionGUID: bRHb3rbpQ6qef80eHb/+eA== X-CSE-MsgGUID: HVKLjGsfRa6k6aUnDHUBoQ== X-IronPort-AV: E=McAfee;i="6800,10657,11706"; a="98069411" X-IronPort-AV: E=Sophos;i="6.21,300,1763452800"; d="scan'208";a="98069411" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Feb 2026 08:07:57 -0800 X-CSE-ConnectionGUID: 6d2q8Js5Qcm5WNvx9MFPSg== X-CSE-MsgGUID: oDWZHOUoQUONBagjlmy7rw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,300,1763452800"; d="scan'208";a="219095070" Received: from dnelso2-mobl.amr.corp.intel.com (HELO [10.125.110.20]) ([10.125.110.20]) by fmviesa005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Feb 2026 08:07:55 -0800 Message-ID: <47780ff4-27ff-4e14-98cc-a10064d7fe13@intel.com> Date: Thu, 19 Feb 2026 09:07:53 -0700 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V7 07/19] dax: Add fs_dax_get() func to prepare dax for fs-dax usage To: John Groves , John Groves , Miklos Szeredi , Dan Williams , Bernd Schubert , Alison Schofield Cc: John Groves , John Groves , Jonathan Corbet , Vishal Verma , 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 , 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" References: <0100019bd33b1f66-b835e86a-e8ae-443f-a474-02db88f7e6db-000000@email.amazonses.com> <20260118223206.92430-1-john@jagalactic.com> <0100019bd33cc18d-83012e03-8214-45a4-91cf-c8b598cd4535-000000@email.amazonses.com> Content-Language: en-US From: Dave Jiang In-Reply-To: <0100019bd33cc18d-83012e03-8214-45a4-91cf-c8b598cd4535-000000@email.amazonses.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/18/26 3:32 PM, John Groves wrote: > From: John Groves > > 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 | 58 ++++++++++++++++++++++++++++++++++++++++++++- > include/linux/dax.h | 20 ++++++++++------ > 4 files changed, 72 insertions(+), 10 deletions(-) > > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c > index e79daf825b52..01402d5103ef 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..00c330ef437c 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 +124,58 @@ 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 || !dev_dax->dev.driver) { Don't you need to hold the dev_dax->dev device lock in order to check the driver? DJ > + iput(&dax_dev->inode); > + return -ENODEV; > + } > + > + dax_drv = to_dax_drv(dev_dax->dev.driver); > + if (dax_drv->type != DAXDRV_FSDEV_TYPE) { > + iput(&dax_dev->inode); > + return -EOPNOTSUPP; > + } > + > + 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 5aaaca135737..6897c5736543 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -52,9 +52,6 @@ struct dax_holder_operations { > #if IS_ENABLED(CONFIG_DAX) > struct dax_device *alloc_dax(void *private, const struct dax_operations *ops); > > -#if IS_ENABLED(CONFIG_DEV_DAX_FS) > -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); > @@ -134,7 +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) > { > @@ -149,12 +145,13 @@ 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); > int dax_folio_reset_order(struct folio *folio); > @@ -168,6 +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;