[RFC PATCH v1 03/10] mm: truncate: Expose preparation steps for truncate_inode_pages_final()

[Ackerley Tng]

Expose preparation steps for truncate_inode_pages_final() to allow
preparation steps to be shared by filesystems that want to implement
truncation differently.

This preparation function will be used by guest_memfd in a later patch.

Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 include/linux/mm.h |  1 +
 mm/truncate.c      | 21 +++++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f0d5be9dc7368..7f04f1eaab15a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3732,6 +3732,7 @@ extern unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info);
 void truncate_inode_pages(struct address_space *mapping, loff_t lstart);
 void truncate_inode_pages_range(struct address_space *mapping, loff_t lstart,
 		uoff_t lend);
+void truncate_inode_pages_final_prepare(struct address_space *mapping);
 void truncate_inode_pages_final(struct address_space *mapping);
 
 /* generic vm_area_ops exported for stackable file systems */
diff --git a/mm/truncate.c b/mm/truncate.c
index 12467c1bd711e..0e85d5451adbe 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -487,7 +487,9 @@ void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
 EXPORT_SYMBOL(truncate_inode_pages);
 
 /**
- * truncate_inode_pages_final - truncate *all* pages before inode dies
+ * truncate_inode_pages_final_prepare - Prepare the mapping for final
+ * truncation but not actually truncate the inode pages. This could be
+ * used by filesystems which want to add custom truncation of folios.
  * @mapping: mapping to truncate
  *
  * Called under (and serialized by) inode->i_rwsem.
@@ -495,7 +497,7 @@ EXPORT_SYMBOL(truncate_inode_pages);
  * Filesystems have to use this in the .evict_inode path to inform the
  * VM that this is the final truncate and the inode is going away.
  */
-void truncate_inode_pages_final(struct address_space *mapping)
+void truncate_inode_pages_final_prepare(struct address_space *mapping)
 {
 	/*
 	 * Page reclaim can not participate in regular inode lifetime
@@ -516,6 +518,21 @@ void truncate_inode_pages_final(struct address_space *mapping)
 		xa_lock_irq(&mapping->i_pages);
 		xa_unlock_irq(&mapping->i_pages);
 	}
+}
+EXPORT_SYMBOL(truncate_inode_pages_final_prepare);
+
+/**
+ * truncate_inode_pages_final - truncate *all* pages before inode dies
+ * @mapping: mapping to truncate
+ *
+ * Called under (and serialized by) inode->i_rwsem.
+ *
+ * Filesystems have to use this in the .evict_inode path to inform the
+ * VM that this is the final truncate and the inode is going away.
+ */
+void truncate_inode_pages_final(struct address_space *mapping)
+{
+	truncate_inode_pages_final_prepare(mapping);
 
 	truncate_inode_pages(mapping, 0);
 }
-- 
2.53.0.345.g96ddfc5eaa-goog