ext4: support large block size in ext4_readdir()

In ext4_readdir(), page_cache_sync_readahead() is used to readahead mapped
physical blocks. With LBS support, this can lead to a negative right shift.

To fix this, the page index is now calculated by first converting the
physical block number (pblk) to a file position (pos) before converting
it to a page index. Also, the correct number of pages to readahead is now
passed.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Message-ID: <20251121090654.631996-9-libaokun@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index d4164c507a9074370daf762a33e104f90198f185..256fe2c1d4c1619eb2cd915d8b6b05bce72656e7 100644 (file)
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -192,13 +192,13 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
                        continue;
                }
                if (err > 0) {
-                       pgoff_t index = map.m_pblk >>
-                                       (PAGE_SHIFT - inode->i_blkbits);
+                       pgoff_t index = map.m_pblk << inode->i_blkbits >>
+                                       PAGE_SHIFT;
                        if (!ra_has_index(&file->f_ra, index))
                                page_cache_sync_readahead(
                                        sb->s_bdev->bd_mapping,
-                                       &file->f_ra, file,
-                                       index, 1);
+                                       &file->f_ra, file, index,
+                                       1 << EXT4_SB(sb)->s_min_folio_order);
                        file->f_ra.prev_pos = (loff_t)index << PAGE_SHIFT;
                        bh = ext4_bread(NULL, inode, map.m_lblk, 0);
                        if (IS_ERR(bh)) {