Re: Fwd: Fwd: Question regarding to Btrfs patchwork /2831525

[Ilan Schwarts <ilan84@gmail.com>]

First of all, Thanks for response !
So if i have 2 btrfs file system on the same machine (not your
everyday scenario, i know)
Lets say a file is created on device A, the file gets inode number X
is it possible on device B to have inode number X also ?
or each device has its own Inode number range ?

I need to create unique identifier for a file, I need to understand if
the identifier would be: GlobalFSID_DeviceID_Inode or DeviceID_Inode
is enough.

Thanks





On Sun, Jan 14, 2018 at 11:13 AM, Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
>
>
> On 2018年01月14日 16:33, Ilan Schwarts wrote:
>> Hello btrfs developers/users,
>>
>> I was wondering regarding to fetching the correct fsid on btrfs from
>> the context of a kernel module.
>
> There are two IDs for btrfs. (in fact more, but you properly won't need
> the extra ids)
>
> FSID: Global one, one fs one FSID.
> Device ID: Bonded to device, each device will have one.
>
> So in case of 2 devices btrfs, each device will has its own device id,
> while both of the devices have the same fsid.
>
> And I think you're talking about the global fsid instead of device id.
>
>> if on suse11.3 kernel 3.0.101-0.47.71-default in order to get fsid, I
>> do the following:
>> convert inode struct to btrfs_inode struct (use btrfsInode =
>> BTRFS_I(inode)), then from btrfs_inode struct i go to root field, and
>> from root i take anon_dev or anon_super.s_dev.
>>         struct btrfs_inode *btrfsInode;
>>         btrfsInode = BTRFS_I(inode);
>>        btrfsInode->root->anon_super.s_dev    or
>>        btrfsInode->root->anon_dev    - depend on kernel.
>
> The most directly method would be:
>
> btrfs_inode->root->fs_info->fsid.
> (For newer kernel, as I'm not familiar with older kernels)
>
> Or from superblock:
> btrfs_inode->root->fs_info->super_copy->fsid.
> (The most reliable one, no matter which kernel version you're using, as
> long as the super block format didn't change)
>
> For device id, it's not that commonly used unless you're dealing with
> chunk mapping, so I'm assuming you're referring to fsid.
>
> Thanks,
> Qu
>
>>
>> In kernel 3.12.28-4-default in order to get the fsid, i need to go
>> to the inode -> superblock -> device id (inode->i_sb->s_dev)
>>
>> Why is this ? and is there a proper/an official way to get it ?
>> --
>> 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
>>
>



-- 


-
Ilan Schwarts