[Ocfs2-devel] [PATCH v2] ocfs2: fall back to buffer IO when append dio is disabled with file hole existing

[piaojun]

On 2017/12/26 16:19, alex chen wrote:
> Hi Changwei,
> 
> On 2017/12/26 15:03, Changwei Ge wrote:
>> The intention of this patch is to provide an option to ocfs2 users whether
>> to allocate disk space while doing dio write.
>>
>> Whether to make ocfs2 fall back to buffer io is up to ocfs2 users through
>> toggling append-dio feature. It rather makes ocfs2 configurable and
>> flexible.
>>
> It is too strange to make ocfs2 fall back to buffer io by toggling append-dio feature.
> 
>> So if something bad happens to dio write with space allocation, we can
>> still make ocfs2 fall back to buffer io. It's an option not a mandatory
>> action.:)
> Now the ocfs2 supports fill holes during direct io whether or not supporting append-dio feature
> and we can directly fix the problem.
> I think it is meaningless to provide an temporary option to turn off it.
> 
I have the same opinion with Alex. And probablly the better way is
providing a new feature for user, not just reuse 'append-dio'.
>>
>> Besides, append-dio feature is key to whether to allocate space with dio
>> writing. So writing to file hole and enlarging file(appending file) should
>> have the same reflection to append-dio feature.
>>
>> Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
>> ---
>>   fs/ocfs2/aops.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++---
>>   1 file changed, 50 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
>> index d151632..32e60c0 100644
>> --- a/fs/ocfs2/aops.c
>> +++ b/fs/ocfs2/aops.c
>> @@ -2414,12 +2414,52 @@ static int ocfs2_dio_end_io(struct kiocb *iocb,
>>   	return ret;
>>   }
>>   
>> +/*
>> + * Will look for holes and unwritten extents in the range starting at
>> + * pos for count bytes (inclusive).
>> + * Return value 1 indicates hole exists, 0 not exists, others indicate error.
>> + */
>> +static int ocfs2_range_has_holes(struct inode *inode, loff_t pos,
>> +				 size_t count)
>> +{
>> +	int ret = 0;
>> +	unsigned int extent_flags;
>> +	u32 cpos, clusters, extent_len, phys_cpos;
>> +	struct super_block *sb = inode->i_sb;
>> +
>> +	cpos = pos >> OCFS2_SB(sb)->s_clustersize_bits;
>> +	clusters = ocfs2_clusters_for_bytes(sb, pos + count) - cpos;
>> +
>> +	while (clusters) {
>> +		ret = ocfs2_get_clusters(inode, cpos, &phys_cpos, &extent_len,
>> +					 &extent_flags);
>> +		if (ret < 0) {
>> +			mlog_errno(ret);
>> +			goto out;
>> +		}
>> +
>> +		if (phys_cpos == 0) {
>> +			ret = 1;
>> +			goto out;
>> +		}
>> +
>> +		if (extent_len > clusters)
>> +			extent_len = clusters;
>> +
>> +		clusters -= extent_len;
>> +		cpos += extent_len;
>> +	}
>> +out:
>> +	return ret;
>> +}
>> +
>>   static ssize_t ocfs2_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>>   {
>>   	struct file *file = iocb->ki_filp;
>>   	struct inode *inode = file->f_mapping->host;
>>   	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>   	get_block_t *get_block;
>> +	int ret;
>>   
>>   	/*
>>   	 * Fallback to buffered I/O if we see an inode without
>> @@ -2429,9 +2469,16 @@ static ssize_t ocfs2_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>>   		return 0;
>>   
>>   	/* Fallback to buffered I/O if we do not support append dio. */
>> -	if (iocb->ki_pos + iter->count > i_size_read(inode) &&
>> -	    !ocfs2_supports_append_dio(osb))
>> -		return 0;
>> +	if (!ocfs2_supports_append_dio(osb)) {
>> +		if (iocb->ki_pos + iter->count > i_size_read(inode))
>> +			return 0;
>> +
>> +		ret = ocfs2_range_has_holes(inode, iocb->ki_pos, iter->count);
>> +		if (ret == 1)
>> +			return 0;
>> +		else if (ret < 0)
>> +			return ret;
>> +	}
>>   
>>   	if (iov_iter_rw(iter) == READ)
>>   		get_block = ocfs2_lock_get_block;
>>
> 
> 
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