linux-ext4 - [RFCv4 2/9] fs/buffer.c: Add generic_buffer

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Date:   Sat, 15 Apr 2023 13:14:23 +0530
From:   "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
To:     linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Cc:     Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
        Disha Goel <disgoel@...ux.ibm.com>,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
Subject: [RFCv4 2/9] fs/buffer.c: Add generic_buffer_fsync implementation

Some of the higher layers like iomap takes inode_lock() when calling
generic_write_sync().
Also writeback already happens from other paths without inode lock,
so it's difficult to say that we really need sync_mapping_buffers() to
take any inode locking here. Having said that, let's add
generic_buffer_fsync() implementation in buffer.c with no
inode_lock/unlock() for now so that filesystems like ext2 and
ext4's nojournal mode can use it.

Ext4 when got converted to iomap for direct-io already copied it's own
variant of __generic_file_fsync() without lock. Hence let's add a helper
API and use it both in ext2 and ext4.

Later we can review other filesystems as well to see if we can make
generic_buffer_fsync() which does not take any inode_lock() as the
default path.

Tested-by: Disha Goel <disgoel@...ux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
---
 fs/buffer.c                 | 43 +++++++++++++++++++++++++++++++++++++
 include/linux/buffer_head.h |  2 ++
 2 files changed, 45 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 9e1e2add541e..df98f1966a71 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -593,6 +593,49 @@ int sync_mapping_buffers(struct address_space *mapping)
 }
 EXPORT_SYMBOL(sync_mapping_buffers);
 
+/**
+ * generic_buffer_fsync - generic buffer fsync implementation
+ * for simple filesystems with no inode lock
+ *
+ * @file:	file to synchronize
+ * @start:	start offset in bytes
+ * @end:	end offset in bytes (inclusive)
+ * @datasync:	only synchronize essential metadata if true
+ *
+ * This is a generic implementation of the fsync method for simple
+ * filesystems which track all non-inode metadata in the buffers list
+ * hanging off the address_space structure.
+ */
+int generic_buffer_fsync(struct file *file, loff_t start, loff_t end,
+			 bool datasync)
+{
+	struct inode *inode = file->f_mapping->host;
+	int err;
+	int ret;
+
+	err = file_write_and_wait_range(file, start, end);
+	if (err)
+		return err;
+
+	ret = sync_mapping_buffers(inode->i_mapping);
+	if (!(inode->i_state & I_DIRTY_ALL))
+		goto out;
+	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
+		goto out;
+
+	err = sync_inode_metadata(inode, 1);
+	if (ret == 0)
+		ret = err;
+
+out:
+	/* check and advance again to catch errors after syncing out buffers */
+	err = file_check_and_advance_wb_err(file);
+	if (ret == 0)
+		ret = err;
+	return ret;
+}
+EXPORT_SYMBOL(generic_buffer_fsync);
+
 /*
  * Called when we've recently written block `bblock', and it is known that
  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 8f14dca5fed7..3170d0792d52 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -211,6 +211,8 @@ int inode_has_buffers(struct inode *);
 void invalidate_inode_buffers(struct inode *);
 int remove_inode_buffers(struct inode *inode);
 int sync_mapping_buffers(struct address_space *mapping);
+int generic_buffer_fsync(struct file *file, loff_t start, loff_t end,
+			 bool datasync);
 void clean_bdev_aliases(struct block_device *bdev, sector_t block,
 			sector_t len);
 static inline void clean_bdev_bh_alias(struct buffer_head *bh)
-- 
2.39.2