Re: [PATCH 03/13] btrfs-progs: lowmem: fix false alert if extent item has been repaired

[Su Yue <suy.fnst@cn.fujitsu.com>]

On 10/23/18 6:30 PM, Qu Wenruo wrote:
> 
> 
> On 2018/10/23 下午5:41, Su Yue wrote:
>> Previously, @err are assigned immediately after check but before
>> repair.
>> repair_extent_item()'s return value also confuses the caller. If
>> error has been repaired and returns 0, check_extent_item() will try
>> to continue check the nonexistent and cause flase alerts.
>>
>> Here make repair_extent_item()'s return codes only represents status
>> of the extent item, error bits are passed by pointer.
>> Move the change of @err after repair.
>>
>> Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com>
>> ---
>>   check/mode-lowmem.c | 106 ++++++++++++++++++++++++++++----------------
>>   1 file changed, 68 insertions(+), 38 deletions(-)
>>
>> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
>> index 76e7be81ceb1..769b3141de8b 100644
>> --- a/check/mode-lowmem.c
>> +++ b/check/mode-lowmem.c
>> @@ -3788,35 +3788,35 @@ out:
>>   /*
>>    * Only delete backref if REFERENCER_MISSING now
>>    *
>> - * Returns <0   the extent was deleted
>> - * Returns >0   the backref was deleted but extent still exists, returned value
>> - *               means error after repair
>> + * Returns <0   the whole extent item was deleted
>> + * Returns >0   the backref was deleted but extent still exists, @err_ret
>> + *		will be set to be error bits after repair.
> 
> Well, I have to admit the parameter list is really human friendly from
> the initial design.
> 

As my previous design, callers of repair_xxx functions just take
care of successes, failures and pathes. If exposing the logic
to the callers is acceptable, will do it as your suggestions.

Thanks,
Su

> In fact, the only real user of @err is just that "if ((err &
> (REFERENCER_MISSING | REFERENCER_MISMATCH)) == 0)" line.
> 
> We can in fact get rid of that @err parameter and do that check at the
> only caller of repair_extent_item().
> 
> 
> And then redefine the return value.
> 
> Like "Return < 0 if we failed to repair backref for the extent.
> Return 0 if we repaired the backref for the extent".
> 
> [snip]
>>   
>> -	if (err && repair) {
>> +	if (tmp_err && repair) {
>>   		ret = repair_extent_item(fs_info->extent_root, path,
>>   			 key.objectid, num_bytes, parent, root_objectid,
>> -			 owner, owner_offset, ret);
>> -		if (ret < 0)
> 
> If follow my above method, here the code can be a little easier:
> 	if (tmp_err && repair) {
> 		if (!(tmp_err & (REFERENCER_MISSING |
> 		    REFENCER_MISMATCH)) {
> 			err |= tmp_err;
> 			goto next;
> 		}
> 		ret = repair_extent_item(...);
> 		if (ret < 0)
> 			err |= tmp_err;
> 	} else if (tmp_err) {
> 		err |= tmp_err;
> 	}
> 

> Without the need to passing @err into repair_extent_item() nor modifying
> @err in that function.
> 
> Thanks,
> Qu
> 
>> +			 owner, owner_offset, &tmp_err);
>> +		err |= tmp_err;
>> +
>> +		if (tmp_err & FATAL_ERROR || ret < 0)
>>   			goto out;
>> -		if (ret) {
>> +		/*
>> +		 * the error has been repaired which means the extent item
>> +		 * is still existed with other backrefs, go to check next.
>> +		 */> +		if (ret > 0) {
>> +			eb = path->nodes[0];
>> +			slot = path->slots[0];
>> +			ei = btrfs_item_ptr(eb, slot, struct btrfs_extent_item);
>> +			item_size = btrfs_item_size_nr(eb, slot);
>>   			goto next;
>> -			err = ret;
>>   		}
>> +	} else {
>> +		err |= tmp_err;
>>   	}
>>   
>> -	ptr += btrfs_extent_inline_ref_size(type);
>> +	ptr_offset += btrfs_extent_inline_ref_size(type);
>>   	goto next;
>>   
>>   out:
>>
> 
>