Re: [PATCH v10 05/41] btrfs: check and enable ZONED mode

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

On 30/11/20 9:15 pm, Damien Le Moal wrote:
> On 2020/11/30 21:13, Anand Jain wrote:
>> On 28/11/20 2:44 am, David Sterba wrote:
>>> On Wed, Nov 18, 2020 at 07:29:20PM +0800, Anand Jain wrote:
>>>> On 10/11/20 7:26 pm, Naohiro Aota wrote:
>>>>> This commit introduces the function btrfs_check_zoned_mode() to check if
>>>>> ZONED flag is enabled on the file system and if the file system consists of
>>>>> zoned devices with equal zone size.
>>>>>
>>>>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
>>>>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>>>>> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
>>>>> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
>>>>> ---
>>>>>     fs/btrfs/ctree.h       | 11 ++++++
>>>>>     fs/btrfs/dev-replace.c |  7 ++++
>>>>>     fs/btrfs/disk-io.c     | 11 ++++++
>>>>>     fs/btrfs/super.c       |  1 +
>>>>>     fs/btrfs/volumes.c     |  5 +++
>>>>>     fs/btrfs/zoned.c       | 81 ++++++++++++++++++++++++++++++++++++++++++
>>>>>     fs/btrfs/zoned.h       | 26 ++++++++++++++
>>>>>     7 files changed, 142 insertions(+)
>>>>>
>>>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>>>> index aac3d6f4e35b..453f41ca024e 100644
>>>>> --- a/fs/btrfs/ctree.h
>>>>> +++ b/fs/btrfs/ctree.h
>>>>> @@ -948,6 +948,12 @@ struct btrfs_fs_info {
>>>>>     	/* Type of exclusive operation running */
>>>>>     	unsigned long exclusive_operation;
>>>>>     
>>>>> +	/* Zone size when in ZONED mode */
>>>>> +	union {
>>>>> +		u64 zone_size;
>>>>> +		u64 zoned;
>>>>> +	};
>>>>> +
>>>>>     #ifdef CONFIG_BTRFS_FS_REF_VERIFY
>>>>>     	spinlock_t ref_verify_lock;
>>>>>     	struct rb_root block_tree;
>>>>> @@ -3595,4 +3601,9 @@ static inline int btrfs_is_testing(struct btrfs_fs_info *fs_info)
>>>>>     }
>>>>>     #endif
>>>>>     
>>>>> +static inline bool btrfs_is_zoned(struct btrfs_fs_info *fs_info)
>>>>> +{
>>>>> +	return fs_info->zoned != 0;
>>>>> +}
>>>>> +
>>>>>     #endif
>>>>> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
>>>>> index 6f6d77224c2b..db87f1aa604b 100644
>>>>> --- a/fs/btrfs/dev-replace.c
>>>>> +++ b/fs/btrfs/dev-replace.c
>>>>> @@ -238,6 +238,13 @@ static int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
>>>>>     		return PTR_ERR(bdev);
>>>>>     	}
>>>>>     
>>>>> +	if (!btrfs_check_device_zone_type(fs_info, bdev)) {
>>>>> +		btrfs_err(fs_info,
>>>>> +			  "dev-replace: zoned type of target device mismatch with filesystem");
>>>>> +		ret = -EINVAL;
>>>>> +		goto error;
>>>>> +	}
>>>>> +
>>>>>     	sync_blockdev(bdev);
>>>>>     
>>>>>     	list_for_each_entry(device, &fs_info->fs_devices->devices, dev_list) {
>>>>
>>>>     I am not sure if it is done in some other patch. But we still have to
>>>>     check for
>>>>
>>>>     (model == BLK_ZONED_HA && incompat_zoned))
>>>
>>> Do you really mean BLK_ZONED_HA, ie. host-aware (HA)?
>>> btrfs_check_device_zone_type checks for _HM.
>>
>>
>> Still confusing to me. The below function, which is part of this
>> patch, says we don't support BLK_ZONED_HM. So does it mean we
>> allow BLK_ZONED_HA only?
>>
>> +static inline bool btrfs_check_device_zone_type(struct btrfs_fs_info
>> *fs_info,
>> +						struct block_device *bdev)
>> +{
>> +	u64 zone_size;
>> +
>> +	if (btrfs_is_zoned(fs_info)) {
>> +		zone_size = (u64)bdev_zone_sectors(bdev) << SECTOR_SHIFT;
>> +		/* Do not allow non-zoned device */
> 
> This comment does not make sense. It should be:
> 
> 		/* Only allow zoned devices with the same zone size */
> 
>> +		return bdev_is_zoned(bdev) && fs_info->zone_size == zone_size;
>> +	}
>> +
>> +	/* Do not allow Host Manged zoned device */
>> +	return bdev_zoned_model(bdev) != BLK_ZONED_HM;
> 
> The comment is also wrong. It should read:
> 
> 	/* Allow only host managed zoned devices */
> 
> This is because we decided to treat host aware devices in the same way as
> regular block devices, since HA drives are backward compatible with regular
> block devices.


Yeah, I read about them, but I have questions like do an FS work on top 
of a BLK_ZONED_HA without modification?
  Are we ok to replace an HM device with a HA device? Or add a HA device 
to a btrfs on an HM device.

Thanks.

> 
>> +}
>>
>>
>> Also, if there is a new type of zoned device in the future, the older
>> kernel should be able to reject the newer zone device types.
>>
>> And, if possible could you rename above function to
>> btrfs_zone_type_is_valid(). Or better.
>>
>>
>>>> right? What if in a non-zoned FS, a zoned device is added through the
>>>> replace. No?
>>>
>>> The types of devices cannot mix, yeah. So I'd like to know the answer as
>>> well.
>>
>>
>>>>> --- a/fs/btrfs/volumes.c
>>>>> +++ b/fs/btrfs/volumes.c
>>>>> @@ -2518,6 +2518,11 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
>>>>>     	if (IS_ERR(bdev))
>>>>>     		return PTR_ERR(bdev);
>>>>>     
>>>>> +	if (!btrfs_check_device_zone_type(fs_info, bdev)) {
>>>>> +		ret = -EINVAL;
>>>>> +		goto error;
>>>>> +	}
>>>>> +
>>>>>     	if (fs_devices->seeding) {
>>>>>     		seeding_dev = 1;
>>>>>     		down_write(&sb->s_umount);
>>>>
>>>> Same here too. It can also happen that a zone device is added to a non
>>>> zoned fs.
>>
>>
>> Thanks.
>>
> 
>