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Date: Mon, 12 Feb 2024 21:46:39 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Zhang Yi <yi.zhang@huaweicloud.com>
Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org, tytso@mit.edu,
	adilger.kernel@dilger.ca, jack@suse.cz, ritesh.list@gmail.com,
	hch@infradead.org, djwong@kernel.org, willy@infradead.org,
	zokeefe@google.com, yi.zhang@huawei.com, chengzhihao1@huawei.com,
	yukuai3@huawei.com, wangkefeng.wang@huawei.com
Subject: Re: [RFC PATCH v3 07/26] iomap: don't increase i_size if it's not a
 write operation
Message-ID: <ZcsCP4h-ExNOcdD6@infradead.org>
References: <20240127015825.1608160-1-yi.zhang@huaweicloud.com>
 <20240127015825.1608160-8-yi.zhang@huaweicloud.com>
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In-Reply-To: <20240127015825.1608160-8-yi.zhang@huaweicloud.com>

Wouldn't it make more sense to just move the size manipulation to the
write-only code?  An untested version of that is below.  With this
the naming of the status variable becomes even more confusing than
it already is, maybe we need to do a cleanup of the *_write_end
calling conventions as it always returns the passed in copied value
or 0.

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 3dab060aed6d7b..8401a9ca702fc0 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -876,34 +876,13 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
 		size_t copied, struct folio *folio)
 {
 	const struct iomap *srcmap = iomap_iter_srcmap(iter);
-	loff_t old_size = iter->inode->i_size;
-	size_t ret;
-
-	if (srcmap->type == IOMAP_INLINE) {
-		ret = iomap_write_end_inline(iter, folio, pos, copied);
-	} else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
-		ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
-				copied, &folio->page, NULL);
-	} else {
-		ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
-	}
-
-	/*
-	 * Update the in-memory inode size after copying the data into the page
-	 * cache.  It's up to the file system to write the updated size to disk,
-	 * preferably after I/O completion so that no stale data is exposed.
-	 */
-	if (pos + ret > old_size) {
-		i_size_write(iter->inode, pos + ret);
-		iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
-	}
-	__iomap_put_folio(iter, pos, ret, folio);
 
-	if (old_size < pos)
-		pagecache_isize_extended(iter->inode, old_size, pos);
-	if (ret < len)
-		iomap_write_failed(iter->inode, pos + ret, len - ret);
-	return ret;
+	if (srcmap->type == IOMAP_INLINE)
+		return iomap_write_end_inline(iter, folio, pos, copied);
+	if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
+		return block_write_end(NULL, iter->inode->i_mapping, pos, len,
+					copied, &folio->page, NULL);
+	return __iomap_write_end(iter->inode, pos, len, copied, folio);
 }
 
 static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
@@ -918,6 +897,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 
 	do {
 		struct folio *folio;
+		loff_t old_size;
 		size_t offset;		/* Offset into folio */
 		size_t bytes;		/* Bytes to write to folio */
 		size_t copied;		/* Bytes copied from user */
@@ -964,7 +944,24 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 
 		copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
 		status = iomap_write_end(iter, pos, bytes, copied, folio);
+		/*
+		 * Update the in-memory inode size after copying the data into
+		 * the page cache.  It's up to the file system to write the
+		 * updated size to disk, preferably after I/O completion so that
+		 * no stale data is exposed.
+		 */
+		old_size = iter->inode->i_size;
+		if (pos + status > old_size) {
+			i_size_write(iter->inode, pos + status);
+			iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
+		}
+		__iomap_put_folio(iter, pos, status, folio);
 
+		if (old_size < pos)
+			pagecache_isize_extended(iter->inode, old_size, pos);
+		if (status < bytes)
+			iomap_write_failed(iter->inode, pos + status,
+						bytes - status);
 		if (unlikely(copied != status))
 			iov_iter_revert(i, copied - status);
 
@@ -1334,6 +1331,7 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 			bytes = folio_size(folio) - offset;
 
 		bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
+		__iomap_put_folio(iter, pos, bytes, folio);
 		if (WARN_ON_ONCE(bytes == 0))
 			return -EIO;
 
@@ -1398,6 +1396,7 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 		folio_mark_accessed(folio);
 
 		bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
+		__iomap_put_folio(iter, pos, bytes, folio);
 		if (WARN_ON_ONCE(bytes == 0))
 			return -EIO;