Re: [PATCH 1/2] fs: btrfs: implement opendir(), readdir() and closedir()

在 2026/6/26 18:51, Alexey Charkov 写道:
> On Fri, Jun 26, 2026 at 10:38 AM Qu Wenruo <[email protected]> wrote:
[...]
>>
>> So it looks like u-boot only supports the above 3 types, and unlike
>> linux kernel the values doesn't match the btrfs internal ones.
>>
>> In that case, I'd still prefer a proper convertor function.
> 
> Hmm, but the convertor function would still be the same switch
> statement, and it's only used in this single place. Would factoring it
> out actually improve readability?

This is mostly a cross-project tendency.

Inside kernel, we do not need a conversion because all the BTRFS_FT* 
flags matches the FT_* inside kernel.

In progs we have btrfs_type_to_imode() to do the conversion to S_IF* flags.

Thus I'd prefer a convertor, even if there is only a single user.

> 
>> [...]
>>> +
>>> +             *offset = key.offset + 1;
>>> +             type = btrfs_dir_type(path.nodes[0], di);
>>> +
>>> +             /* XATTRs share the key space but are not directory entries. */
>>> +             if (type == BTRFS_FT_XATTR) {
>>
>> This doesn't looks correct again.
>>
>> XATTR has their own keys, they should not show up among DIR_INDEX keys.

Firstly, xattr is per-inode, not per-dentry.
Thus I doubt if you can hit an XATTR type inside a DIR_INDEX.

The easily way to test the theory is just create a simple XATTR for 
compression:

  # mkfs.btrfs -f test.img
  # mount test.img /mnt/btrfs
  # touch /mnt/btrfs/foobar
  # btrfs prop set /mnt/btrfs/foobar compression zstd
  # sync
  # btrfs ins dump-tree -t 5 test.img
  [...]
	item 6 key (257 XATTR_ITEM 550297449) itemoff 15812 itemsize 51
		location key (0 UNKNOWN.0 0) type XATTR
		transid 10 data_len 4 name_len 17
		name: btrfs.compression
		data zstd

You can see that XATTR_ITEM key is for that inode 257, not for the 
parent directory inode (256).


Secondly, if you check the tree-checker.c from the kernel, 
check_dir_item() will reject an XATTR dir type if the key is not 
XATTR_ITEM_KEY.

So even if you really find a btrfs with XATTR dir type but with 
DIR_INDEX key, btrfs will refuse to reject that tree block.

Thanks,
Qu

> 
> Let me double check and adjust accordingly.
> 
> Thanks a lot for your review!
> 
> Best regards,
> Alexey