Re: [PATCH] Snapshot/subvolume listing feature

[TARUISI Hiroaki <taruishi.hiroak@jp.fujitsu.com>]

Patches for Snapshot/subvolume listing feature are
modified.

With these patches, ioctl searches for subvolumes
under only one tree, and btrfsctl repeatedly creates
parameters and calls ioctl until all subvolumes
are listed.

An intrenal logic was changed but user interfaces
(option and contents of a list) remain same as
a patch I posted before.

Regards,
taruisi

TARUISI Hiroaki wrote:
> Thank you for your advice.
> 
> I'm aware of redundant search, but I didn't think of
> getdents like interface.
> 
> I'll remake it without redundant search.
> 
> Regards,
> taruisi
> 
> Yan, Zheng wrote:
>> 2009/11/16 TARUISI Hiroaki <taruishi.hiroak@jp.fujitsu.com>:
>>> I made Snapshot/subvolume listing feature.
>>>
>>> This feature consists of two patches, for kernel(ioctl),
>>> and for progs(btrfsctl). I send these two patches as response
>>> of this mail soon.
>>>
>>> New option '-l' is introduced to btrfsctl for listing.
>>>
>>> If this option is specified, btrfsctl call new ioctl. New ioctl
>>> searches root tree and enumerates subtrees. For each subtrees,
>>> ioctl searches directory path to tree root, and enumerates
>>> more descendant until no more subtree is found.
>>>
>>> MANPAGE-like option description and examples are as follows.
>>>
>>>  OPTIONS
>>>        -l _file_
>>>                List all snapshot/subvolume directories under a tree
>>>                which _file_ belongs to.
>>>
>>>  EXAMPLES
>>>        # btrfsctl -l /work/btrfs
>>>    Base path = /work/btrfs/
>>>    No.    Tree ID      Subvolume Relative Path
>>>     1         256      ss1/
>>>     2         257      ss2/
>>>     3         258      svs1/ss1/
>>>     4         259      svs1/ss2/
>>>     5         260      svs2/ss1/
>>>     6         261      svs2/ss2/
>>>     7         262      ss3/
>>>     8         263      ss4/
>>>     9         264      sv_pool/
>>>    10         265      sv_pool/ss01/
>>>    11         266      sv_pool/ss02/
>>>    12         267      sv_pool/ss03/
>>>    13         268      sv_pool/ss04/
>>>    14         269      sv_pool/ss05/
>>>    15         270      sv_pool/ss06/
>>>    16         271      sv_pool/ss07/
>>>    17         272      sv_pool/ss08/
>>>    18         273      sv_pool/ss09/
>>>    19         274      sv_pool/ss10/
>>>  operation complete
>>>  Btrfs v0.19-9-gd67dad2
>>>
>> Thank you for doing this.
>>
>> I have a quick look at the patches. It seems the ioctl returns full path
>> to each subvolume and uses sequence ID to indicate the progress
>> of listing. Every time the ioctl is called, it tries building full list of
>> subvolume, then skip entries that already returned.  I think the API is
>> suboptimal, a getdents like API is better. (The ioctl only lists subvolumes
>> within a given subvolume, the user program call the ioctl recursively
>> to list all subvolumes.)
>>
>> Yan, Zheng
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