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From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Jonathan Corbet <corbet@lwn.net>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	linux-doc@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH 2/5] buffer: Add kernel-doc for block_dirty_folio()
Date: Thu,  4 Jan 2024 16:36:49 +0000
Message-Id: <20240104163652.3705753-3-willy@infradead.org>
In-Reply-To: <20240104163652.3705753-1-willy@infradead.org>
References: <20240104163652.3705753-1-willy@infradead.org>
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Turn the excellent documentation for this function into kernel-doc.
Replace 'page' with 'folio' and make a few other minor updates.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/buffer.c | 54 +++++++++++++++++++++++++++++------------------------
 1 file changed, 30 insertions(+), 24 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 5c29850e4781..31e171382e00 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -687,30 +687,36 @@ void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 }
 EXPORT_SYMBOL(mark_buffer_dirty_inode);
 
-/*
- * Add a page to the dirty page list.
- *
- * It is a sad fact of life that this function is called from several places
- * deeply under spinlocking.  It may not sleep.
- *
- * If the page has buffers, the uptodate buffers are set dirty, to preserve
- * dirty-state coherency between the page and the buffers.  It the page does
- * not have buffers then when they are later attached they will all be set
- * dirty.
- *
- * The buffers are dirtied before the page is dirtied.  There's a small race
- * window in which a writepage caller may see the page cleanness but not the
- * buffer dirtiness.  That's fine.  If this code were to set the page dirty
- * before the buffers, a concurrent writepage caller could clear the page dirty
- * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
- * page on the dirty page list.
- *
- * We use private_lock to lock against try_to_free_buffers while using the
- * page's buffer list.  Also use this to protect against clean buffers being
- * added to the page after it was set dirty.
- *
- * FIXME: may need to call ->reservepage here as well.  That's rather up to the
- * address_space though.
+/**
+ * block_dirty_folio - Mark a folio as dirty.
+ * @mapping: The address space containing this folio.
+ * @folio: The folio to mark dirty.
+ *
+ * Filesystems which use buffer_heads can use this function as their
+ * ->dirty_folio implementation.  Some filesystems need to do a little
+ * work before calling this function.  Filesystems which do not use
+ * buffer_heads should call filemap_dirty_folio() instead.
+ *
+ * If the folio has buffers, the uptodate buffers are set dirty, to
+ * preserve dirty-state coherency between the folio and the buffers.
+ * It the folio does not have buffers then when they are later attached
+ * they will all be set dirty.
+ *
+ * The buffers are dirtied before the folio is dirtied.  There's a small
+ * race window in which writeback may see the folio cleanness but not the
+ * buffer dirtiness.  That's fine.  If this code were to set the folio
+ * dirty before the buffers, writeback could clear the folio dirty flag,
+ * see a bunch of clean buffers and we'd end up with dirty buffers/clean
+ * folio on the dirty folio list.
+ *
+ * We use private_lock to lock against try_to_free_buffers() while
+ * using the folio's buffer list.  This also prevents clean buffers
+ * being added to the folio after it was set dirty.
+ *
+ * Context: May only be called from process context.  Does not sleep.
+ * Caller must ensure that @folio cannot be truncated during this call,
+ * typically by holding the folio lock or having a page in the folio
+ * mapped and holding the page table lock.
  */
 bool block_dirty_folio(struct address_space *mapping, struct folio *folio)
 {
-- 
2.43.0