Re: [Ocfs2-devel] [PATCH 2/3] ocfs2: add ocfs2_overwrite_io function

[Gang He]

Hi Joseph,


>>> 

> 
> On 17/11/28 15:24, Gang He wrote:
>> Hello Joseph,
>> 
>> 
>>>>>
>> 
>>>
>>> On 17/11/28 11:35, Gang He wrote:
>>>> Hello Joseph,
>>>>
>>>>
>>>>>>>
>>>>> Hi Gang,
>>>>>
>>>>> On 17/11/27 17:46, Gang He wrote:
>>>>>> Add ocfs2_overwrite_io function, which is used to judge if
>>>>>> overwrite allocated blocks, otherwise, the write will bring extra
>>>>>> block allocation overhead.
>>>>>>
>>>>>> Signed-off-by: Gang He <ghe@xxxxxxxx>
>>>>>> ---
>>>>>>  fs/ocfs2/extent_map.c | 67 
>>>>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>  fs/ocfs2/extent_map.h |  3 +++
>>>>>>  2 files changed, 70 insertions(+)
>>>>>>
>>>>>> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
>>>>>> index e4719e0..98bf325 100644
>>>>>> --- a/fs/ocfs2/extent_map.c
>>>>>> +++ b/fs/ocfs2/extent_map.c
>>>>>> @@ -832,6 +832,73 @@ int ocfs2_fiemap(struct inode *inode, struct 
>>>>> fiemap_extent_info *fieinfo,
>>>>>>  	return ret;
>>>>>>  }
>>>>>>  
>>>>>> +/* Is IO overwriting allocated blocks? */
>>>>>> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
>>>>>> +		       int wait)
>>>>>> +{
>>>>>> +	int ret = 0, is_last;
>>>>>> +	u32 mapping_end, cpos;
>>>>>> +	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>>>>> +	struct buffer_head *di_bh = NULL;
>>>>>> +	struct ocfs2_extent_rec rec;
>>>>>> +
>>>>>> +	if (wait)
>>>>>> +		ret = ocfs2_inode_lock(inode, &di_bh, 0);
>>>>>> +	else
>>>>>> +		ret = ocfs2_try_inode_lock(inode, &di_bh, 0);
>>>>>> +	if (ret)
>>>>>> +		goto out;
>>>>>> +
>>>>>> +	if (wait)
>>>>>> +		down_read(&OCFS2_I(inode)->ip_alloc_sem);
>>>>>> +	else {
>>>>>> +		if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) {
>>>>>> +			ret = -EAGAIN;
>>>>>> +			goto out_unlock1;
>>>>>> +		}
>>>>>> +	}
>>>>>> +
>>>>>> +	if ((OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) &&
>>>>>> +	   ((map_start + map_len) <= i_size_read(inode)))
>>>>>> +		goto out_unlock2;
>>>>>> +
>>>>>> +	cpos = map_start >> osb->s_clustersize_bits;
>>>>>> +	mapping_end = ocfs2_clusters_for_bytes(inode->i_sb,
>>>>>> +					       map_start + map_len);
>>>>>> +	is_last = 0;
>>>>>> +	while (cpos < mapping_end && !is_last) {
>>>>>> +		ret = ocfs2_get_clusters_nocache(inode, di_bh, cpos,
>>>>>> +						 NULL, &rec, &is_last);
>>>>>> +		if (ret) {
>>>>>> +			mlog_errno(ret);
>>>>>> +			goto out_unlock2;
>>>>>> +		}
>>>>>> +
>>>>>> +		if (rec.e_blkno == 0ULL)
>>>>>> +			break;
>>>>>> +
>>>>>> +		if (rec.e_flags & OCFS2_EXT_REFCOUNTED)
>>>>>> +			break;
>>>>>> +
>>>>>> +		cpos = le32_to_cpu(rec.e_cpos) +
>>>>>> +			le16_to_cpu(rec.e_leaf_clusters);
>>>>>> +	}
>>>>>> +
>>>>>> +	if (cpos < mapping_end)
>>>>>> +		ret = 1;
>>>>>> +
>>>>>> +out_unlock2:
>>>>>> +	brelse(di_bh);
>>>>>> +
>>>>>> +	up_read(&OCFS2_I(inode)->ip_alloc_sem);
>>>>>> +
>>>>>> +out_unlock1:
>>>>> Should brelse(di_bh) be here?
>>>> If the code jumps to out_unlock1 directly, the di_bh pointer should be NULL, 
> 
>>> it is not necessary to release.
>>>>
>>> Umm... No, once going out here, we have already taken inode lock. So
>>> di_bh should be released.
>> Sorry, you are right.
>> 
>>>
>>>>>
>>>>>> +	ocfs2_inode_unlock(inode, 0);
>>>>>> +
>>>>>> +out:
>>>>>> +	return (ret ? 0 : 1);
>>>>> I don't think EAGAIN and other error code can be handled the same. We
>>>>> have to distinguish them.
>>>> Ok, I think we can add one line log to report the error in case the error is 
> 
>>> not EAGAIN. 
>>>>
>>> My point is, there is no need to try again in several cases, e.g. EROFS
>>> returned by ocfs2_get_clusters_nocache.
>> In this function ocfs2_overwrite_io() only can return True(1) or False(0), 
> then I think we can only give a error print before return true/false.
>> It is not necessary to return another value, but should let the user know 
> any possible error message.
>>This is because you just ignore the error and convert it to 0 or 1.
> But in your next patch, if !ocfs2_overwrite_io(), it will return EGAIN
> to upper layer and let it try again.
> But in some cases, e.g. EROFS, trying again is meaningless. That's why
> we can't simply return 0 or 1 here. Also we have to distinguish the
> error code in the next patch.
I think that we have to use the return value if we want to propagate the errorno to the above.
I will change the return value meanings of ocfs2_overwrite_io() function.
return 0 means this is a overwrite allocated block IO.
return -EGAIN means there are some blocks which are not allocated.
return other -ERRNO means there is another error happened.
Does it make sense?

Thanks
Gang

> 
>> Thanks
>> Gang 
>> 
>>>
>>>>>
>>>>> Thanks,
>>>>> Joseph
>>>>>
>>>>>> +}
>>>>>> +
>>>>>>  int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int 
>>>>> whence)
>>>>>>  {
>>>>>>  	struct inode *inode = file->f_mapping->host;
>>>>>> diff --git a/fs/ocfs2/extent_map.h b/fs/ocfs2/extent_map.h
>>>>>> index 67ea57d..fd9e86a 100644
>>>>>> --- a/fs/ocfs2/extent_map.h
>>>>>> +++ b/fs/ocfs2/extent_map.h
>>>>>> @@ -53,6 +53,9 @@ int ocfs2_extent_map_get_blocks(struct inode *inode, u64 
>>>>> v_blkno, u64 *p_blkno,
>>>>>>  int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>>>>>>  		 u64 map_start, u64 map_len);
>>>>>>  
>>>>>> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
>>>>>> +		       int wait);
>>>>>> +
>>>>>>  int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int 
>>>>> origin);
>>>>>>  
>>>>>>  int ocfs2_xattr_get_clusters(struct inode *inode, u32 v_cluster,
>>>>>>
>>>>