Re: [PATCH] btrfs: Add show_path function for btrfs_super_ops.

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Ping？

Any new comments?
It has been a long time and the patch still not merged....

Thanks,
Qu
-------- Original Message --------
Subject: Re: [PATCH] btrfs: Add show_path function for btrfs_super_ops.
From: Qu Wenruo <quwenruo@cn.fujitsu.com>
To: <dsterba@suse.cz>, <linux-btrfs@vger.kernel.org>
Date: 2014年07月31日 11:50
> Hi David,
>
> No mean to disturb you, but it has been serveral days since last comment.
>
> If you have any comment about the new patch, since due to my lack of 
> explain the patch seems not
> reviewed, I am very glad to hear.
>
> If any other ideas occur to you, like the pro and cons about old mount 
> trick vs show_path() implement,
> it would be also quite nice.
>
> Thanks,
> Qu
>
>
> -------- Original Message --------
> Subject: Re: [PATCH] btrfs: Add show_path function for btrfs_super_ops.
> From: Qu Wenruo <quwenruo@cn.fujitsu.com>
> To: dsterba@suse.cz, linux-btrfs@vger.kernel.org
> Date: 2014年07月25日 08:40
>> Thanks for the comment.
>>
>> -------- Original Message --------
>> Subject: Re: [PATCH] btrfs: Add show_path function for btrfs_super_ops.
>> From: David Sterba <dsterba@suse.cz>
>> To: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> Date: 2014年07月24日 21:09
>>> On Mon, Jul 21, 2014 at 05:02:29PM +0800, Qu Wenruo wrote:
>>>> show_path() function in struct super_operations is used to output
>>>> subtree mount info for mountinfo.
>>>> Without the implement of show_path() function, user can not found 
>>>> where
>>>> each subvolume is mounted if using 'subvolid=' mount option.
>>>> (When mounted with 'subvol=' mount option, vfs is aware of subtree 
>>>> mount
>>>> and can to the path resolve by vfs itself)
>>> Your previous patches unify both to call mount_subtree, then the 
>>> default
>>> vfs implementation of show_path will do the right thing, ie
>>> seq_dentry(...), and the path will be resolved for free.
>>>
>>> Means this patch is not needed, so I'll skip commenting it.
>>
>> I'm sorry that I forgot to mention this patch is going to replace the 
>> previous patch(use mount_subtree method).
>>
>> Since vfs provide the show_path() function to do the fs specific 
>> subtree showing things,
>> I would like to use it other than previous mount_subtree() trick.
>>
>> Also. as mentioned by Chandan Rajendra, previous subtree patch can't 
>> handle subvolume behind normal directory.
>> This show_path() patch is somewhat v2 version of previous patch.
>>>
>>>> With this patch, end users will be able to use findmnt(8) or other
>>>> programs reading mountinfo to find which btrfs subvolume is mounted.
>>>>
>>>> Though we use fs_info->subvol_sem to protect show_path() from 
>>>> subvolume
>>>> destroying/creating, if user renames/moves the parent non-subvolume
>>>> dir of a subvolume, it is still possible that concurrency may 
>>>> happen and
>>>> cause btrfs_search_slot() fails to find the desired key.
>>>> In that case, we just return -EBUSY and info user to try again since
>>>> extra locking like locking the whole subvolume tree is too 
>>>> expensive for
>>>> such usage.
>>> And the subvolume renames will be handled as well.
>
> -- 
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html