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From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Christoph Hellwig <hch@lst.de>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	linux-fsdevel@vger.kernel.org,
	linux-ext4@vger.kernel.org
Subject: [PATCH 3/7] buffer: Add buffer_write_begin, buffer_write_end and __buffer_write_end
Date: Tue, 28 May 2024 17:48:24 +0100
Message-ID: <20240528164829.2105447-4-willy@infradead.org>
In-Reply-To: <20240528164829.2105447-1-willy@infradead.org>
References: <20240528164829.2105447-1-willy@infradead.org>
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These functions are to be called from filesystem implementations of
write_begin and write_end.  They correspond to block_write_begin,
generic_write_end and block_write_end.  The old functions need to
be kept around as they're used as function pointers.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/buffer.c                 | 80 ++++++++++++++++++++++++++-----------
 include/linux/buffer_head.h |  6 +++
 2 files changed, 63 insertions(+), 23 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 58ac52f20bf6..4064b21fe499 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2217,39 +2217,55 @@ static void __block_commit_write(struct folio *folio, size_t from, size_t to)
 }
 
 /*
- * block_write_begin takes care of the basic task of block allocation and
+ * buffer_write_begin - Helper for filesystem write_begin implementations
+ * @mapping: Address space being written to.
+ * @pos: Position in bytes within the file.
+ * @len: Number of bytes being written.
+ * @get_block: How to get buffer_heads for this filesystem.
+ *
+ * Take care of the basic task of block allocation and
  * bringing partial write blocks uptodate first.
  *
  * The filesystem needs to handle block truncation upon failure.
+ *
+ * Return: The folio to write to, or an ERR_PTR on failure.
  */
-int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
-		struct page **pagep, get_block_t *get_block)
+struct folio *buffer_write_begin(struct address_space *mapping, loff_t pos,
+		size_t len, get_block_t *get_block)
 {
-	pgoff_t index = pos >> PAGE_SHIFT;
-	struct page *page;
+	struct folio *folio = __filemap_get_folio(mapping, pos / PAGE_SIZE,
+			FGP_WRITEBEGIN, mapping_gfp_mask(mapping));
 	int status;
 
-	page = grab_cache_page_write_begin(mapping, index);
-	if (!page)
-		return -ENOMEM;
+	if (IS_ERR(folio))
+		return folio;
 
-	status = __block_write_begin(page, pos, len, get_block);
+	status = __block_write_begin_int(folio, pos, len, get_block, NULL);
 	if (unlikely(status)) {
-		unlock_page(page);
-		put_page(page);
-		page = NULL;
+		folio_unlock(folio);
+		folio_put(folio);
+		folio = ERR_PTR(status);
 	}
 
-	*pagep = page;
-	return status;
+	return folio;
+}
+EXPORT_SYMBOL(buffer_write_begin);
+
+int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
+		struct page **pagep, get_block_t *get_block)
+{
+	struct folio *folio = buffer_write_begin(mapping, pos, len, get_block);
+
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
+	*pagep = &folio->page;
+	return 0;
 }
 EXPORT_SYMBOL(block_write_begin);
 
-int block_write_end(struct file *file, struct address_space *mapping,
-			loff_t pos, unsigned len, unsigned copied,
-			struct page *page, void *fsdata)
+size_t __buffer_write_end(struct file *file, struct address_space *mapping,
+		loff_t pos, size_t len, size_t copied, struct folio *folio)
 {
-	struct folio *folio = page_folio(page);
 	size_t start = pos - folio_pos(folio);
 
 	if (unlikely(copied < len)) {
@@ -2277,17 +2293,26 @@ int block_write_end(struct file *file, struct address_space *mapping,
 
 	return copied;
 }
-EXPORT_SYMBOL(block_write_end);
+EXPORT_SYMBOL(__buffer_write_end);
 
-int generic_write_end(struct file *file, struct address_space *mapping,
+int block_write_end(struct file *file, struct address_space *mapping,
 			loff_t pos, unsigned len, unsigned copied,
 			struct page *page, void *fsdata)
+{
+	return buffer_write_end(file, mapping, pos, len, copied,
+			page_folio(page));
+}
+EXPORT_SYMBOL(block_write_end);
+
+size_t buffer_write_end(struct file *file, struct address_space *mapping,
+			loff_t pos, size_t len, size_t copied,
+			struct folio *folio)
 {
 	struct inode *inode = mapping->host;
 	loff_t old_size = inode->i_size;
 	bool i_size_changed = false;
 
-	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
+	copied = __buffer_write_end(file, mapping, pos, len, copied, folio);
 
 	/*
 	 * No need to use i_size_read() here, the i_size cannot change under us
@@ -2301,8 +2326,8 @@ int generic_write_end(struct file *file, struct address_space *mapping,
 		i_size_changed = true;
 	}
 
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 
 	if (old_size < pos)
 		pagecache_isize_extended(inode, old_size, pos);
@@ -2316,6 +2341,15 @@ int generic_write_end(struct file *file, struct address_space *mapping,
 		mark_inode_dirty(inode);
 	return copied;
 }
+EXPORT_SYMBOL(buffer_write_end);
+
+int generic_write_end(struct file *file, struct address_space *mapping,
+			loff_t pos, unsigned len, unsigned copied,
+			struct page *page, void *fsdata)
+{
+	return buffer_write_end(file, mapping, pos, len, copied,
+			page_folio(page));
+}
 EXPORT_SYMBOL(generic_write_end);
 
 /*
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 1b7f14e39ab8..44e4b2b18cc0 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -267,6 +267,12 @@ int block_write_end(struct file *, struct address_space *,
 int generic_write_end(struct file *, struct address_space *,
 				loff_t, unsigned, unsigned,
 				struct page *, void *);
+struct folio *buffer_write_begin(struct address_space *mapping, loff_t pos,
+		size_t len, get_block_t *get_block);
+size_t buffer_write_end(struct file *, struct address_space *, loff_t pos,
+		size_t len, size_t copied, struct folio *);
+size_t __buffer_write_end(struct file *, struct address_space *, loff_t pos,
+		size_t len, size_t copied, struct folio *);
 void folio_zero_new_buffers(struct folio *folio, size_t from, size_t to);
 int cont_write_begin(struct file *, struct address_space *, loff_t pos,
 		unsigned len, struct page **, void **fsdata, get_block_t *,
-- 
2.43.0