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

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Date:   Wed, 03 Jan 2018 20:32:08 -0700
From:   "Gang He" <ghe@...e.com>
To:     <alex.chen@...wei.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 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@...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'?
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).


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,
>>>>
>> 
>> 
>> .
>>