[PATCH v4 02/23] ext4: factor out ext4_truncate_[up|down]()

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

Refactor ext4_setattr() by introducing two helper functions,
ext4_truncate_up() and ext4_truncate_down(), to handle size changes. The
current ATTR_SIZE processing consolidates checks for both shrinking and
non-shrinking cases, leading to cluttered code. Separating the
truncation paths improves readability.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/ext4/inode.c | 199 +++++++++++++++++++++++++++---------------------
 1 file changed, 112 insertions(+), 87 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0751dc55e94f..35e958f89bd5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5855,6 +5855,112 @@ static void ext4_wait_for_tail_page_commit(struct inode *inode)
 	}
 }
 
+/*
+ * Set i_size and i_disksize to 'newsize'.
+ *
+ * Both i_rwsem and i_data_sem are required here to avoid races between
+ * generic append writeback and concurrent truncate that also modify
+ * i_size and i_disksize.
+ */
+static inline void ext4_set_inode_size(struct inode *inode, loff_t newsize)
+{
+	WARN_ON_ONCE(S_ISREG(inode->i_mode) && !inode_is_locked(inode));
+
+	down_write(&EXT4_I(inode)->i_data_sem);
+	i_size_write(inode, newsize);
+	EXT4_I(inode)->i_disksize = newsize;
+	up_write(&EXT4_I(inode)->i_data_sem);
+}
+
+static int ext4_truncate_up(struct inode *inode, loff_t oldsize, loff_t newsize)
+{
+	ext4_lblk_t old_lblk, new_lblk;
+	handle_t *handle;
+	int ret;
+
+	if (!IS_ALIGNED(oldsize | newsize, i_blocksize(inode))) {
+		ret = ext4_inode_attach_jinode(inode);
+		if (ret)
+			return ret;
+	}
+
+	inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
+	if (!IS_ALIGNED(oldsize, i_blocksize(inode))) {
+		ret = ext4_block_zero_eof(inode, oldsize, LLONG_MAX);
+		if (ret)
+			return ret;
+	}
+
+	handle = ext4_journal_start(inode, EXT4_HT_INODE, 3);
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+
+	old_lblk = oldsize > 0 ? (oldsize - 1) >> inode->i_blkbits : 0;
+	new_lblk = newsize > 0 ? (newsize - 1) >> inode->i_blkbits : 0;
+	ext4_fc_track_range(handle, inode, old_lblk, new_lblk);
+
+	ext4_set_inode_size(inode, newsize);
+
+	ret = ext4_mark_inode_dirty(handle, inode);
+	ext4_journal_stop(handle);
+	if (ret)
+		return ret;
+	/*
+	 * isize extend must be called outside an active handle due to
+	 * the lock ordering of transaction start and folio lock in the
+	 * iomap buffered I/O path (folio lock -> transaction start).
+	 */
+	pagecache_isize_extended(inode, oldsize, newsize);
+	return 0;
+}
+
+static int ext4_truncate_down(struct inode *inode, loff_t oldsize,
+			      loff_t newsize, int *orphan)
+{
+	ext4_lblk_t start_lblk;
+	handle_t *handle;
+	int ret;
+
+	/* Do not change i_size. */
+	if (newsize == oldsize)
+		goto truncate;
+
+	/* Shrink. */
+	handle = ext4_journal_start(inode, EXT4_HT_INODE, 3);
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+
+	if (ext4_handle_valid(handle)) {
+		ret = ext4_orphan_add(handle, inode);
+		*orphan = 1;
+		if (ret) {
+			ext4_journal_stop(handle);
+			return ret;
+		}
+	}
+
+	start_lblk = newsize > 0 ? (newsize - 1) >> inode->i_blkbits : 0;
+	ext4_fc_track_range(handle, inode, start_lblk, EXT_MAX_BLOCKS - 1);
+
+	ext4_set_inode_size(inode, newsize);
+
+	ret = ext4_mark_inode_dirty(handle, inode);
+	ext4_journal_stop(handle);
+	if (ret)
+		return ret;
+
+	if (ext4_should_journal_data(inode))
+		ext4_wait_for_tail_page_commit(inode);
+truncate:
+	/*
+	 * Truncate pagecache after we've waited for commit in data=journal
+	 * mode to make pages freeable.  Call ext4_truncate() even if
+	 * i_size didn't change to truncatea possible preallocated blocks.
+	 */
+	truncate_pagecache(inode, newsize);
+	return ext4_truncate(inode);
+}
+
 /*
  * ext4_setattr()
  *
@@ -5951,7 +6057,6 @@ int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 	}
 
 	if (attr->ia_valid & ATTR_SIZE) {
-		handle_t *handle;
 		loff_t oldsize = inode->i_size;
 		int shrink = (attr->ia_size < inode->i_size);
 
@@ -6003,94 +6108,14 @@ int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 			goto err_out;
 		}
 
-		if (attr->ia_size != inode->i_size) {
-			/* attach jbd2 jinode for EOF folio tail zeroing */
-			if (attr->ia_size & (inode->i_sb->s_blocksize - 1) ||
-			    oldsize & (inode->i_sb->s_blocksize - 1)) {
-				error = ext4_inode_attach_jinode(inode);
-				if (error)
-					goto out_mmap_sem;
-			}
-
-			/*
-			 * Update c/mtime and tail zero the EOF folio on
-			 * truncate up. ext4_truncate() handles the shrink case
-			 * below.
-			 */
-			if (!shrink) {
-				inode_set_mtime_to_ts(inode,
-						      inode_set_ctime_current(inode));
-				if (oldsize & (inode->i_sb->s_blocksize - 1)) {
-					error = ext4_block_zero_eof(inode,
-							oldsize, LLONG_MAX);
-					if (error)
-						goto out_mmap_sem;
-				}
-			}
-
-			handle = ext4_journal_start(inode, EXT4_HT_INODE, 3);
-			if (IS_ERR(handle)) {
-				error = PTR_ERR(handle);
-				goto out_mmap_sem;
-			}
-			if (ext4_handle_valid(handle) && shrink) {
-				error = ext4_orphan_add(handle, inode);
-				orphan = 1;
-				if (error)
-					goto out_handle;
-			}
-
-			if (shrink)
-				ext4_fc_track_range(handle, inode,
-					(attr->ia_size > 0 ? attr->ia_size - 1 : 0) >>
-					inode->i_sb->s_blocksize_bits,
-					EXT_MAX_BLOCKS - 1);
-			else
-				ext4_fc_track_range(
-					handle, inode,
-					(oldsize > 0 ? oldsize - 1 : oldsize) >>
-					inode->i_sb->s_blocksize_bits,
-					(attr->ia_size > 0 ? attr->ia_size - 1 : 0) >>
-					inode->i_sb->s_blocksize_bits);
-
-			/*
-			 * We have to update i_size under i_data_sem together
-			 * with i_disksize to avoid races with writeback code
-			 * updating disksize in mpage_map_and_submit_extent().
-			 */
-			down_write(&EXT4_I(inode)->i_data_sem);
-			i_size_write(inode, attr->ia_size);
-			EXT4_I(inode)->i_disksize = attr->ia_size;
-			up_write(&EXT4_I(inode)->i_data_sem);
-
-			error = ext4_mark_inode_dirty(handle, inode);
-out_handle:
-			ext4_journal_stop(handle);
-			if (error)
-				goto out_mmap_sem;
-			if (!shrink) {
-				pagecache_isize_extended(inode, oldsize,
-							 inode->i_size);
-			} else if (ext4_should_journal_data(inode)) {
-				ext4_wait_for_tail_page_commit(inode);
-			}
+		if (attr->ia_size > oldsize)
+			error = ext4_truncate_up(inode, oldsize, attr->ia_size);
+		else {
+			/* Shrink or do not change i_size. */
+			error = ext4_truncate_down(inode, oldsize,
+						   attr->ia_size, &orphan);
 		}
 
-		/*
-		 * Truncate pagecache after we've waited for commit
-		 * in data=journal mode to make pages freeable.
-		 */
-		truncate_pagecache(inode, inode->i_size);
-		/*
-		 * Call ext4_truncate() even if i_size didn't change to
-		 * truncate possible preallocated blocks.
-		 */
-		if (attr->ia_size <= oldsize) {
-			rc = ext4_truncate(inode);
-			if (rc)
-				error = rc;
-		}
-out_mmap_sem:
 		filemap_invalidate_unlock(inode->i_mapping);
 	}
 
-- 
2.52.0