linux-kernel - Re: [Ocfs2-devel] [PATCH v3 2/3] ocfs2: add ocfs2_overwrite

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Date:   Thu, 4 Jan 2018 09:10:10 +0800
From:   alex chen <alex.chen@...wei.com>
To:     Gang He <ghe@...e.com>
CC:     <jlbec@...lplan.org>, <ocfs2-devel@....oracle.com>,
        <mfasheh@...sity.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [Ocfs2-devel] [PATCH v3 2/3] ocfs2: add ocfs2_overwrite_io function

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@...e.com>
>>> ---
>>>  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'?

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,
>>>
> 
> 
> .
>