From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.14]) (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 C90D2405AD2; Tue, 24 Mar 2026 15:25:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774365960; cv=none; b=jPK2RAEchQxf3wlHy+auC6dn40mMyKzAD0YiAA9XLot4b3ldjrtNi2NHjxXSJF7JY3/TKNiOa8nfaJeOt9pBrzaRKA9ZWvxU0ObMCT8NxUBZGZ5RGLDJ/N8I98lSQRiiNckt8X26X6qTc+WnezURT4HytVwdHE20h0n1M17WwAw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774365960; c=relaxed/simple; bh=jeQXGWXW5DYZbmlwpZZUSd6Abgx4FfGMTceWU3VAjno=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=l5/9yuMe34eLAb202YTkHHFV+hmKZjTyF3Xtv5lCIsCTunRgu152wxiJR8VLdg60dWZwv5jvhYXGVbpMkskwrAcCiQZ6IIKhY8zgcKPQcBjmGiEG1bqnmkL7HL5nvOaKrRgthj2JkFyD4JP3y8OK4sgVd9VXwOlgSTXG2X41z3s= 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=MOQOHWaM; arc=none smtp.client-ip=198.175.65.14 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="MOQOHWaM" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1774365958; x=1805901958; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=jeQXGWXW5DYZbmlwpZZUSd6Abgx4FfGMTceWU3VAjno=; b=MOQOHWaMOzUU3qCmr6g0+J5R0+txAx50XD3xPqcpWgM0sOHHMB65xO8n GV6lcXvF59OJiZyItpU/HT+ox87rv2yPkkAvrfi32YPmBNGgM6PMno5Fk RHXzFbdsYtRgfpVZXIVVNBDfOqUUl6VNo4xsNMZhpfm0QTEB4KspgEG3X VkupcLrcKNKabX/fXTfqXU1A16xG2uLPd9RJ8CI0X0LIdZTAqHgvUFfeN 2B8OTGfZH9su/+JsFNrFh3ZcSpPwGVKOef9tKjbKDZKMyX/pZS8PmMkzd 6nTTUt5/0ObZoIS+282e45gJERU/6JWz3EYIGw2JbZlKFXMif7r/NxWXc g==; X-CSE-ConnectionGUID: Pe2D9X/0R2y2hhh4QONW3Q== X-CSE-MsgGUID: D2MTY8cnSySCjwdHl2oJ8w== X-IronPort-AV: E=McAfee;i="6800,10657,11739"; a="79244201" X-IronPort-AV: E=Sophos;i="6.23,138,1770624000"; d="scan'208";a="79244201" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2026 08:25:42 -0700 X-CSE-ConnectionGUID: TKxnMyNnTBKIiJdg/c15Mg== X-CSE-MsgGUID: D3byFbOkTk+nc7XpEvIq5A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,138,1770624000"; d="scan'208";a="226024176" Received: from jdoman-mobl3.amr.corp.intel.com (HELO [10.125.110.6]) ([10.125.110.6]) by fmviesa004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2026 08:25:38 -0700 Message-ID: Date: Tue, 24 Mar 2026 08:25:36 -0700 Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V9 7/8] 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 , Jonathan Corbet , Shuah Khan , 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 , 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" References: <0100019d1d463523-617e8165-a084-4d91-aa5e-13778264d5d4-000000@email.amazonses.com> <20260324003919.5106-1-john@jagalactic.com> <0100019d1d484ddc-2487f887-7ecd-49a3-abfe-9dabec28873f-000000@email.amazonses.com> Content-Language: en-US From: Dave Jiang In-Reply-To: <0100019d1d484ddc-2487f887-7ecd-49a3-abfe-9dabec28873f-000000@email.amazonses.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/23/26 5:39 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 Reviewed-by: Dave Jiang > --- > drivers/dax/bus.c | 2 -- > drivers/dax/bus.h | 2 ++ > drivers/dax/super.c | 66 ++++++++++++++++++++++++++++++++++++++++++++- > include/linux/dax.h | 17 +++++++++--- > 4 files changed, 80 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 b19bfe0c2fd1..bf37b9a982f3 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -130,7 +130,6 @@ 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) > { > @@ -145,12 +144,13 @@ 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); > @@ -164,6 +164,15 @@ 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;