linux-ext4 - Re: [PATCH v2 4/4] ext4: Switch to iomap for SEEK_HOLE / SEEK

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Message-ID: <CAHpGcMJY2PZJYLzUS5ejcnfSVkeO-GKL7z1fRONs1AUdyiaULg@mail.gmail.com>
Date:   Thu, 14 Sep 2017 14:47:28 +0200
From:   Andreas Grünbacher <andreas.gruenbacher@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 4/4] ext4: Switch to iomap for SEEK_HOLE / SEEK_DATA

2017-09-14 14:02 GMT+02:00 Jan Kara <jack@...e.cz>:
> On Thu 14-09-17 11:50:47, Andreas Gruenbacher wrote:
>> @@ -3422,9 +3422,38 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>>       map.m_lblk = first_block;
>>       map.m_len = last_block - first_block + 1;
>>
>> -     if (!(flags & IOMAP_WRITE)) {
>> +     if (flags & IOMAP_REPORT) {
>>               ret = ext4_map_blocks(NULL, inode, &map, 0);
>> -     } else {
>> +             if (ret < 0)
>> +                     return ret;
>> +
>> +             if (ret == 0) {
>> +                     ext4_lblk_t end = map.m_lblk + map.m_len - 1;
>> +                     struct extent_status es;
>> +
>> +                     ext4_es_find_delayed_extent_range(inode, map.m_lblk, end, &es);
>> +
>> +                     if (!es.es_len || es.es_lblk > end) {
>> +                             /* entire range is a hole */
>> +                     } else if (es.es_lblk > map.m_lblk) {
>> +                             /* range starts with a hole */
>> +                             map.m_len = es.es_lblk - map.m_lblk;
>> +                     } else {
>> +                             ext4_lblk_t offs = 0;
>> +
>> +                             if (es.es_lblk < map.m_lblk)
>> +                                     offs = map.m_lblk - es.es_lblk;
>> +                             map.m_lblk = es.es_lblk + offs;
>> +                             map.m_pblk = ext4_es_pblock(&es) + offs;
>> +                             map.m_len = es.es_len - offs;
>> +                             if (ext4_es_is_unwritten(&es))
>> +                                     map.m_flags |= EXT4_MAP_UNWRITTEN;
>
> This is not possible. If there is unwritten extent at map->m_lblk, then
> ext4_map_blocks() could not have possibly returned 0. So just delete this
> condition and set map.m_pblk to 0 since delalloc extent has no physical
> position.
>
>> +                             if (ext4_es_is_delayed(&es))
>> +                                     delalloc = true;
>
> Also ext4_es_is_delayed(&es) is guaranteed to be true since you've looked
> it up by ext4_es_find_delayed_extent_range(). So just set delalloc = true
> unconditionally.

Since map.m_pblk is never used in the delalloc case, we can leave it
undefined above as well.

> Otherwise the patch looks good so after fixing up these small issues feel
> free to add:
>
> Reviewed-by: Jan Kara <jack@...e.cz>

Thanks,
Andreas