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SubjectRe: [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@suse.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,
>>>>
>>
>>
>> .
>>

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