Re: [PATCH 02/15] btrfs-progs: Remove root argument from btrfs_del_csums

[Nikolay Borisov <nborisov@suse.com>]

On 11.06.2018 11:08, Qu Wenruo wrote:
> 
> 
> On 2018年06月11日 15:48, Nikolay Borisov wrote:
>>
>>
>> On 11.06.2018 10:40, Qu Wenruo wrote:
>>>
>>>
>>> On 2018年06月11日 15:02, Nikolay Borisov wrote:
>>>>
>>>>
>>>> On 11.06.2018 07:46, Qu Wenruo wrote:
>>>>>
>>>>>
>>>>> On 2018年06月08日 20:47, Nikolay Borisov wrote:
>>>>>> It's not needed, since we can obtain a reference to fs_info from the
>>>>>> passed transaction handle. This is needed by delayed refs code.
>>>>>
>>>>> This looks a little too aggressive to me.
>>>>>
>>>>> Normally we would expect parameters like @trans then @fs_info.
>>>>> Although @trans only let us get @fs_info, under certain case @trans
>>>>> could be NULL (like btrfs_search_slot).
>>>>>
>>>>> Although for btrfs_del_csums() @tran can be NULL, I still prefer the
>>>>> @trans, @fs_info parameters.
>>>>
>>>> The reason I'm making those prep patches i because I would like to get
>>>> rid of the root argument from _free_extent,
>>>
>>> For this part, I completely agree with you.
>>>
>>> The root doesn't make sense, getting rid of it is completely fine.
>>> The abuse of btrfs_root as parameter should be stopped, and we have tons
>>> of such cleanup both in kernel and btrfs-progs.
>>>
>>> The only concern is about possible NULL @trans parameter.
>>> However it could be easily addressed by adding 'restrict' prefix.
>>>
>>> So just adding 'restrict', and then the whole cleanup part is fine to me.
>>
>> you mean making it "struct btrfs_trans_handle * restrict trans". But
>> restrict deals with pointer aliasing it doesn't have any bearing on the
>> NULL-ability of trans. I'm afraid I don't follow your logic here, care
>> to explain further?
> 
> All my fault, I misunderstood the 'restrict' qualifier.
> 
> There seems to be no qualifier to give early warning on passing NULL
> pointer in.
> 
> So the cleanup part should be OK.
> (If there is such qualifier, I'm all ears)

I guess it's called ASSERT(trans) :)
> 
> Thanks,
> Qu
> 
>>
>>>
>>> Thanks,
>>> Qu
>>>
>>>> since if you look at the
>>>> later delayed refs patches - patch 12/15 you'd see that the adapter
>>>> function __free_extent2 doesn't really have a root pointer as an
>>>> argument. If you also take a look at 10/15 (add delayed refs
>>>> infrastructure), the functions which create the delayed refs also don't
>>>> take a struct btrfs_root as an argument.
>>>>
>>>> Alternatively I can perhaps wire up a call to btrfs_read_fs_root in
>>>> __free_extent which will be using the "ref->root" id to obtain struct
>>>> btrfs_root. However, due to the way FST fixup is implemented (I still
>>>> haven't sent that code) it's possible that we call __free_extent2 with
>>>> the freespace root set to 0 so if btrfs_read_fs_root is called it will
>>>> return an -ENOENT.
>>>>
>>>> In conclusion what you suggest *could* be done but it will require
>>>> re-engineering the currently-tested FST code + delayed refs code. Given
>>>> the purpose of the root argument in this callchain I'd rather eliminate
>>>> it altogether and not bother with it.
>>>>
>>>>>
>>>>> Thanks,
>>>>> Qu
>>>>>
>>>>>
>>>>>>
>>>>>> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
>>>>>> ---
>>>>>>  btrfs-corrupt-block.c |  2 +-
>>>>>>  ctree.h               |  3 +--
>>>>>>  extent-tree.c         |  2 +-
>>>>>>  file-item.c           | 20 ++++++++++----------
>>>>>>  4 files changed, 13 insertions(+), 14 deletions(-)
>>>>>>
>>>>>> diff --git a/btrfs-corrupt-block.c b/btrfs-corrupt-block.c
>>>>>> index 4fbea26cda20..3add8e63b7bb 100644
>>>>>> --- a/btrfs-corrupt-block.c
>>>>>> +++ b/btrfs-corrupt-block.c
>>>>>> @@ -926,7 +926,7 @@ static int delete_csum(struct btrfs_root *root, u64 bytenr, u64 bytes)
>>>>>>  		return PTR_ERR(trans);
>>>>>>  	}
>>>>>>  
>>>>>> -	ret = btrfs_del_csums(trans, root, bytenr, bytes);
>>>>>> +	ret = btrfs_del_csums(trans, bytenr, bytes);
>>>>>>  	if (ret)
>>>>>>  		fprintf(stderr, "Error deleting csums %d\n", ret);
>>>>>>  	btrfs_commit_transaction(trans, root);
>>>>>> diff --git a/ctree.h b/ctree.h
>>>>>> index de4b1b7e6416..082726238b91 100644
>>>>>> --- a/ctree.h
>>>>>> +++ b/ctree.h
>>>>>> @@ -2752,8 +2752,7 @@ int btrfs_del_inode_ref(struct btrfs_trans_handle *trans,
>>>>>>  			u64 ino, u64 parent_ino, u64 *index);
>>>>>>  
>>>>>>  /* file-item.c */
>>>>>> -int btrfs_del_csums(struct btrfs_trans_handle *trans,
>>>>>> -		    struct btrfs_root *root, u64 bytenr, u64 len);
>>>>>> +int btrfs_del_csums(struct btrfs_trans_handle *trans, u64 bytenr, u64 len);
>>>>>>  int btrfs_insert_file_extent(struct btrfs_trans_handle *trans,
>>>>>>  			     struct btrfs_root *root,
>>>>>>  			     u64 objectid, u64 pos, u64 offset,
>>>>>> diff --git a/extent-tree.c b/extent-tree.c
>>>>>> index cbc022f6cef6..c6f09b52800f 100644
>>>>>> --- a/extent-tree.c
>>>>>> +++ b/extent-tree.c
>>>>>> @@ -2372,7 +2372,7 @@ static int __free_extent(struct btrfs_trans_handle *trans,
>>>>>>  		btrfs_release_path(path);
>>>>>>  
>>>>>>  		if (is_data) {
>>>>>> -			ret = btrfs_del_csums(trans, root, bytenr, num_bytes);
>>>>>> +			ret = btrfs_del_csums(trans, bytenr, num_bytes);
>>>>>>  			BUG_ON(ret);
>>>>>>  		}
>>>>>>  
>>>>>> diff --git a/file-item.c b/file-item.c
>>>>>> index 7b0ff3585509..71d4e89f78d1 100644
>>>>>> --- a/file-item.c
>>>>>> +++ b/file-item.c
>>>>>> @@ -394,8 +394,7 @@ static noinline int truncate_one_csum(struct btrfs_root *root,
>>>>>>   * deletes the csum items from the csum tree for a given
>>>>>>   * range of bytes.
>>>>>>   */
>>>>>> -int btrfs_del_csums(struct btrfs_trans_handle *trans,
>>>>>> -		    struct btrfs_root *root, u64 bytenr, u64 len)
>>>>>> +int btrfs_del_csums(struct btrfs_trans_handle *trans, u64 bytenr, u64 len)
>>>>>>  {
>>>>>>  	struct btrfs_path *path;
>>>>>>  	struct btrfs_key key;
>>>>>> @@ -403,11 +402,10 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
>>>>>>  	u64 csum_end;
>>>>>>  	struct extent_buffer *leaf;
>>>>>>  	int ret;
>>>>>> -	u16 csum_size =
>>>>>> -		btrfs_super_csum_size(root->fs_info->super_copy);
>>>>>> -	int blocksize = root->fs_info->sectorsize;
>>>>>> +	u16 csum_size = btrfs_super_csum_size(trans->fs_info->super_copy);
>>>>>> +	int blocksize = trans->fs_info->sectorsize;
>>>>>> +	struct btrfs_root *csum_root = trans->fs_info->csum_root;
>>>>>>  
>>>>>> -	root = root->fs_info->csum_root;
>>>>>>  
>>>>>>  	path = btrfs_alloc_path();
>>>>>>  	if (!path)
>>>>>> @@ -418,7 +416,7 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
>>>>>>  		key.offset = end_byte - 1;
>>>>>>  		key.type = BTRFS_EXTENT_CSUM_KEY;
>>>>>>  
>>>>>> -		ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
>>>>>> +		ret = btrfs_search_slot(trans, csum_root, &key, path, -1, 1);
>>>>>>  		if (ret > 0) {
>>>>>>  			if (path->slots[0] == 0)
>>>>>>  				goto out;
>>>>>> @@ -445,7 +443,7 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
>>>>>>  
>>>>>>  		/* delete the entire item, it is inside our range */
>>>>>>  		if (key.offset >= bytenr && csum_end <= end_byte) {
>>>>>> -			ret = btrfs_del_item(trans, root, path);
>>>>>> +			ret = btrfs_del_item(trans, csum_root, path);
>>>>>>  			BUG_ON(ret);
>>>>>>  		} else if (key.offset < bytenr && csum_end > end_byte) {
>>>>>>  			unsigned long offset;
>>>>>> @@ -485,12 +483,14 @@ int btrfs_del_csums(struct btrfs_trans_handle *trans,
>>>>>>  			 * btrfs_split_item returns -EAGAIN when the
>>>>>>  			 * item changed size or key
>>>>>>  			 */
>>>>>> -			ret = btrfs_split_item(trans, root, path, &key, offset);
>>>>>> +			ret = btrfs_split_item(trans, csum_root, path, &key,
>>>>>> +					       offset);
>>>>>>  			BUG_ON(ret && ret != -EAGAIN);
>>>>>>  
>>>>>>  			key.offset = end_byte - 1;
>>>>>>  		} else {
>>>>>> -			ret = truncate_one_csum(root, path, &key, bytenr, len);
>>>>>> +			ret = truncate_one_csum(csum_root, path, &key, bytenr,
>>>>>> +						len);
>>>>>>  			BUG_ON(ret);
>>>>>>  		}
>>>>>>  		btrfs_release_path(path);
>>>>>>
>>>>> --
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>>>
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