[RFC PATCH 7/9] jfs: Read quota through the page cache

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

The comment above jfs_quota_read() is stale; sb_bread() will use the
page cache, so we may as well use the page cache directly and avoid
using jfs_get_block().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/jfs/super.c | 54 ++++++++++++++++++++------------------------------
 1 file changed, 21 insertions(+), 33 deletions(-)

diff --git a/fs/jfs/super.c b/fs/jfs/super.c
index 85d4f44f2ac4..1e7d117b555d 100644
--- a/fs/jfs/super.c
+++ b/fs/jfs/super.c
@@ -721,51 +721,39 @@ static int jfs_show_options(struct seq_file *seq, struct dentry *root)
 }
 
 #ifdef CONFIG_QUOTA
-
-/* Read data from quotafile - avoid pagecache and such because we cannot afford
- * acquiring the locks... As quota files are never truncated and quota code
- * itself serializes the operations (and no one else should touch the files)
- * we don't have to be afraid of races */
 static ssize_t jfs_quota_read(struct super_block *sb, int type, char *data,
-			      size_t len, loff_t off)
+			      size_t len, loff_t pos)
 {
 	struct inode *inode = sb_dqopt(sb)->files[type];
-	sector_t blk = off >> sb->s_blocksize_bits;
-	int err = 0;
-	int offset = off & (sb->s_blocksize - 1);
-	int tocopy;
+	struct address_space *mapping = inode->i_mapping;
 	size_t toread;
-	struct buffer_head tmp_bh;
-	struct buffer_head *bh;
+	pgoff_t index;
 	loff_t i_size = i_size_read(inode);
 
-	if (off > i_size)
+	if (pos > i_size)
 		return 0;
-	if (off+len > i_size)
-		len = i_size-off;
+	if (pos + len > i_size)
+		len = i_size - pos;
 	toread = len;
+	index = pos / PAGE_SIZE;
+
 	while (toread > 0) {
-		tocopy = sb->s_blocksize - offset < toread ?
-				sb->s_blocksize - offset : toread;
+		struct folio *folio = read_mapping_folio(mapping, index, NULL);
+		size_t tocopy = PAGE_SIZE - offset_in_page(pos);
+		void *src;
+
+		if (IS_ERR(folio))
+			return PTR_ERR(folio);
+
+		src = kmap_local_folio(folio, offset_in_folio(folio, pos));
+		memcpy(data, src, tocopy);
+		kunmap_local(src);
+		folio_put(folio);
 
-		tmp_bh.b_state = 0;
-		tmp_bh.b_size = i_blocksize(inode);
-		err = jfs_get_block(inode, blk, &tmp_bh, 0);
-		if (err)
-			return err;
-		if (!buffer_mapped(&tmp_bh))	/* A hole? */
-			memset(data, 0, tocopy);
-		else {
-			bh = sb_bread(sb, tmp_bh.b_blocknr);
-			if (!bh)
-				return -EIO;
-			memcpy(data, bh->b_data+offset, tocopy);
-			brelse(bh);
-		}
-		offset = 0;
 		toread -= tocopy;
 		data += tocopy;
-		blk++;
+		pos += tocopy;
+		index++;
 	}
 	return len;
 }
-- 
2.34.1