Re: [Ocfs2-devel] [PATCH v3 2/3] ocfs2: add ocfs2_overwrite_io function

[alex chen]

Hi Gang,

On 2018/1/4 11:32, Gang He wrote:
> Hi Alex,
> 
> 
>>>>
>> Hi Gang,
>>
>> On 2018/1/3 13:14, Gang He wrote:
>>> Hi Alex,
>>>
>>>
>>>>>>
>>>> Hi Gang,
>>>>
>>>> On 2017/12/28 18:07, 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 | 45 +++++++++++++++++++++++++++++++++++++++++++++
>>>>>  fs/ocfs2/extent_map.h |  3 +++
>>>>>  2 files changed, 48 insertions(+)
>>>>>
>>>>> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
>>>>> index e4719e0..06cb964 100644
>>>>> --- a/fs/ocfs2/extent_map.c
>>>>> +++ b/fs/ocfs2/extent_map.c
>>>>> @@ -38,6 +38,7 @@
>>>>>  #include "inode.h"
>>>>>  #include "super.h"
>>>>>  #include "symlink.h"
>>>>> +#include "aops.h"
>>>>>  #include "ocfs2_trace.h" 
>>>>>  
>>>>>  #include "buffer_head_io.h"
>>>>> @@ -832,6 +833,50 @@ 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, struct buffer_head *di_bh,
>>>>> +		       u64 map_start, u64 map_len)
>>>> Here can the type of 'map_start' is struct loff_t and map_len is struct 
>>>> size_t?
>>> I prefer to use the detailed types for file start address and length in 
>> ocfs2_overwrite_io() function declaration, 
>>> then here will be a potential type conversion (loff_t  -> u64, size_t -> u64), I 
>> think this conversion should be considered as expectation. 
>>> Since our OCFS2 is a 64 bit file system, the related data types do not 
>> change,  but loff_t and size_t type can change under different architectures 
>> (e.g. x86_32, x86_64, etc.).
>>>
>> The type conversion (loff_t  -> u64, size_t -> u64) has been made before calling 
>> the function ocfs2_overwrite_io().
>> So it doesn't matter which type we use for file start address and length in 
>> ocfs2_overwrite_io(), Right?
>> To be consistent with the context, is it better to use struct loff_t for 
>> 'map_start' and struct size_t for 'map_len'?
> I am not sure if I describe my thought clearly.
> In VFS layer, loff_t, size_t and other related data types are used for all architectures, that means these kinds of data type's lengths
> will change based on different CPU bits.
> But, for a specific file system, the file system bit is fixed, e.g. ocfs2 is a 64 bits file system, this bit length is determined by file system layout (not CPU bits).
> Then, in this layer we should use fixed-length (or common) data type in the code, the VFS layer data types should be converted into our data types potentially (but except pointer type).
> 
I agree about you to use fixed-length data type in OCFS2 layer, but now we already use the loff_t for pos in ocfs2_prepare_inode_for_write(), I don't
think it's going to work whatever data type we use. Right ?
Anyway, I accept it if you think it is better to use fixed-length type here.

Reviewed-by: Alex Chen <alex.chen@xxxxxxxxxx>

Thanks,
Alex
> 
> Thanks
> Gang   
> 
>>
>> Thanks,
>> Alex
>>
>>> Thanks
>>> Gang
>>>
>>>>
>>>> Thanks,
>>>> Alex
>>>>> +{
>>>>> +	int ret = 0, is_last;
>>>>> +	u32 mapping_end, cpos;
>>>>> +	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>>>> +	struct ocfs2_extent_rec rec;
>>>>> +
>>>>> +	if (OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) {
>>>>> +		if (ocfs2_size_fits_inline_data(di_bh, map_start + map_len))
>>>>> +			return ret;
>>>>> +		else
>>>>> +			return -EAGAIN;
>>>>> +	}
>>>>> +
>>>>> +	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;
>>>>> +		}
>>>>> +
>>>>> +		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 = -EAGAIN;
>>>>> +out:
>>>>> +	return ret;
>>>>> +}
>>>>> +
>>>>>  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..1057586 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, struct buffer_head *di_bh,
>>>>> +		       u64 map_start, u64 map_len);
>>>>> +
>>>>>  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,
>>>>>
>>>
>>>
>>> .
>>>
> 
> .
>