From 59eb73b98ae0b12fc9b39c08f0f5a5552cb02d1e Mon Sep 17 00:00:00 2001 From: John Groves Date: Fri, 27 Mar 2026 21:04:22 +0000 Subject: dax: Factor out dax_folio_reset_order() helper Both fs/dax.c:dax_folio_put() and drivers/dax/fsdev.c: fsdev_clear_folio_state() (the latter coming in the next commit after this one) contain nearly identical code to reset a compound DAX folio back to order-0 pages. Factor this out into a shared helper function. The new dax_folio_reset_order() function: - Clears the folio's mapping and share count - Resets compound folio state via folio_reset_order() - Clears PageHead and compound_head for each sub-page - Restores the pgmap pointer for each resulting order-0 folio - Returns the original folio order (for callers that need to advance by that many pages) Two intentional differences from the original dax_folio_put() logic: 1. folio->share is cleared unconditionally. This is correct because the DAX subsystem maintains the invariant that share != 0 only when mapping == NULL (enforced by dax_folio_make_shared()). dax_folio_put() ensures share has reached zero before calling this helper, so the unconditional clear is safe. 2. folio->pgmap is now explicitly restored for order-0 folios. For the dax_folio_put() caller this is a no-op (reads and writes back the same field). It is intentional for the upcoming fsdev_clear_folio_state() caller, which converts previously-compound folios and needs pgmap re-established for all pages regardless of order. This simplifies fsdev_clear_folio_state() from ~50 lines to ~15 lines. Suggested-by: Jonathan Cameron Reviewed-by: Ira Weiny Reviewed-by: Dave Jiang Reviewed-by: Jonathan Cameron Signed-off-by: John Groves Link: https://patch.msgid.link/0100019d311cc6b9-5be7428a-7f16-4774-8f90-a44b88ac5660-000000@email.amazonses.com Signed-off-by: Ira Weiny --- include/linux/dax.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/dax.h b/include/linux/dax.h index bf103f317cac0..73cfc1a7c8f15 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -153,6 +153,7 @@ static inline void fs_put_dax(struct dax_device *dax_dev, void *holder) #if IS_ENABLED(CONFIG_FS_DAX) 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); struct page *dax_layout_busy_page(struct address_space *mapping); struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end); -- cgit v1.2.3 From 700ecbc1f5aa02ba9ad68d7be1ef7a9c8eae07e9 Mon Sep 17 00:00:00 2001 From: John Groves Date: Fri, 27 Mar 2026 21:05:03 +0000 Subject: dax: Add dax_set_ops() for setting dax_operations at bind time Add a new dax_set_ops() function that allows drivers to set the dax_operations after the dax_device has been allocated. This is needed for fsdev_dax where the operations need to be set during probe and cleared during unbind. The fsdev driver uses devm_add_action_or_reset() for cleanup consistency, avoiding the complexity of mixing devm-managed resources with manual cleanup in a remove() callback. This ensures cleanup happens automatically in the correct reverse order when the device is unbound. Reviewed-by: Dave Jiang Reviewed-by: Jonathan Cameron Signed-off-by: John Groves Link: https://patch.msgid.link/0100019d311d65a0-b9c1419e-f3a0-4afd-b0bd-848f18ff5950-000000@email.amazonses.com Signed-off-by: Ira Weiny --- include/linux/dax.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/dax.h b/include/linux/dax.h index 73cfc1a7c8f15..b19bfe0c2fd13 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -243,6 +243,7 @@ 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, -- cgit v1.2.3 From eec38f5d86d27535509c99f02ccc642ceb0c3e2a Mon Sep 17 00:00:00 2001 From: John Groves Date: Fri, 27 Mar 2026 21:05:12 +0000 Subject: dax: Add fs_dax_get() func to prepare dax for fs-dax usage 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. Reviewed-by: Jonathan Cameron Reviewed-by: Dave Jiang Signed-off-by: John Groves Link: https://patch.msgid.link/0100019d311d8750-75395c22-031b-4d5f-aebe-790dca656b87-000000@email.amazonses.com Signed-off-by: Ira Weiny --- include/linux/dax.h | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/dax.h b/include/linux/dax.h index b19bfe0c2fd13..a85e270bfb3c6 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 +144,12 @@ 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); 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 +163,15 @@ 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; -- cgit v1.2.3 From 2ae624d5a555d47a735fb3f4d850402859a4db77 Mon Sep 17 00:00:00 2001 From: John Groves Date: Fri, 27 Mar 2026 21:05:21 +0000 Subject: dax: export dax_dev_get() famfs needs to look up a dax_device by dev_t when resolving fmap entries that reference character dax devices. Reviewed-by: Dave Jiang Reviewed-by: Jonathan Cameron Signed-off-by: John Groves Link: https://patch.msgid.link/0100019d311daab5-bb212f0b-4e05-4668-bf53-d76fab56be68-000000@email.amazonses.com Signed-off-by: Ira Weiny --- include/linux/dax.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/dax.h b/include/linux/dax.h index a85e270bfb3c6..9ef95b136bb8b 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -54,6 +54,7 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops); void *dax_holder(struct dax_device *dax_dev); void put_dax(struct dax_device *dax_dev); void kill_dax(struct dax_device *dax_dev); +struct dax_device *dax_dev_get(dev_t devt); void dax_write_cache(struct dax_device *dax_dev, bool wc); bool dax_write_cache_enabled(struct dax_device *dax_dev); bool dax_synchronous(struct dax_device *dax_dev); -- cgit v1.2.3