On 2025-11-10 20:26, Pankaj Raghav wrote:
> On 11/7/25 15:42, libaokun@huaweicloud.com wrote:
>> From: Baokun Li <libaokun1@huawei.com>
>>
>> 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>
>> ---
> Minor general comments below.
>
> Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Thanks for the review!
>
>> fs/ext4/dir.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
>> index d4164c507a90..256fe2c1d4c1 100644
>> --- 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;
> It will be nice to have some common helper for this operation. We do something
> similar in filemap.c as well.
In patch 10, we introduced a macro to handle the conversion from lblk
to page index. In this particular case, though, it is pblk, which has
a different value range compared to lblk. As this is the only instance
in the code, I applied a standalone modification here.
>
>> 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);
> Just a personal opinion but it would be nice to have some variable for this instead of doing it
> inline? It could be defined along with index.
>
> unsigned long min_nr_pages = 1UL << EXT4_SB(sb)->s_min_folio_order;
>
Thank you for the suggestion. This is indeed a bit easier to understand,
but the space here is limited and the variable is only used once,
so I prefer the current direct style.
Cheers,
Baokun
>> file->f_ra.prev_pos = (loff_t)index << PAGE_SHIFT;
>> bh = ext4_bread(NULL, inode, map.m_lblk, 0);
>> if (IS_ERR(bh)) {
>