Re: [PATCH v2 2/2] btrfs: sysfs add devinfo/fsid to retrieve fsid from the device

[Anand Jain <anand.jain@oracle.com>]

David,

  Gentle ping on this patch?

Thanks, Anand


On 17/11/2021 11:29, Anand Jain wrote:
> 
> 
> On 17/11/2021 01:16, David Sterba wrote:
>> On Thu, Oct 21, 2021 at 11:31:17PM +0800, Anand Jain wrote:
>>> In the case of the seed device, the fsid can be different from the 
>>> mounted
>>> sprout fsid.  The userland has to read the device superblock to know the
>>> fsid but, that idea fails if the device is missing. So add a sysfs
>>> interface devinfo/<devid>/fsid to show the fsid of the device.
>>>
>>> For example:
>>>   $ cd /sys/fs/btrfs/b10b02a5-f9de-4276-b9e8-2bfd09a578a8
>>>
>>>   $ cat devinfo/1/fsid
>>>   c44d771f-639d-4df3-99ec-5bc7ad2af93b
>>>   $ cat  devinfo/3/fsid
>>>   b10b02a5-f9de-4276-b9e8-2bfd09a578a8
>>
>>  From user perspective, it's another fsid, one is in the path, so I'm
>> wondering if it should be named like read_fsid or sprout_fsid or if the
>> seed/sprout information should be put into another directory completely.
> 
> I am viewing it as fsid as per the device's sb. This fsid matches with
> the blkid(8) output. A path to the device's fsid will help to script.
> So I am not voting for sprout_fsid because it does not exist in the
> most common non-sprouted fsid.
> 
> Now to show whether a device is seed or sprout, the user friendly
> approach will be like for example:
>       /sys/fs/btrfs/<fsid>/devinfo/<devid>/device_state
> to show all that apply, for example:
>       SEED|SPROUT|READ_ONLY|WRITABLE|ZONED|METADATA_ONLY|\
>       DATA_ONLY|READ_PREFERRED|REPLACE_TGT|REPLACE_SRC|\
>       SCRUB_RUNNING
> 
> However, per kernel general rule of thumb one value per sys-fs file,
> so it should be for example:
>       /sys/fs/btrfs/<fsid>/devinfo/<devid>/seed
> 0
>       /sys/fs/btrfs/<fsid>/devinfo/<devid>/sprout
> 1
> 
> So based on this my patch "btrfs: introduce new device-state
> read_preferred" in the mailing list already proposed
>       /sys/fs/btrfs/<fsid>/devinfo/<devid>/read_preferred
> 
> So to summarize,  I can rename fsid to read_fsid. And, progressively
> in a separate patch, we can add <>/seed <>/sprout sysfs files as above.
> What do you think?