On 2019/12/9 3:37 下午, Christoph Hellwig wrote:
> On Fri, Dec 06, 2019 at 05:44:38PM +0800, Coly Li wrote:
>>> {
>>> - struct cache_sb *out = page_address(bio_first_page_all(bio));
>>> + struct cache_sb *out;
>>> unsigned int i;
>>> + struct buffer_head *bh;
>>> +
>>> + /*
>>> + * The page is held since read_super, this __bread * should not
>>> + * cause an extra io read.
>>> + */
>>> + bh = __bread(bdev, 1, SB_SIZE);
>>> + if (!bh)
>>> + goto out_bh;
>>> +
>>> + out = (struct cache_sb *) bh->b_data;
>>
>> This is quite tricky here. Could you please to move this code piece into
>> an inline function and add code comments to explain why a read is
>> necessary for a write.
>
> A read is not nessecary. He only added it because he was too fearful
> of calculating the data offset directly. But calculating it directly
> is almost trivial and should just be done here. Alternatively if that
> is still to hard just keep a pointer to the cache_sb around, which is
> how most file systems do it.
>
Copied, if Liang does not have time to handle this as your suggestion, I
will handle it.
Thanks for the hint.
--
Coly Li
