Re: [PATCH v5 06/28] btrfs: disallow NODATACOW in HMZONED mode

[Naohiro Aota <naohiro.aota@wdc.com>]

On Thu, Dec 05, 2019 at 04:31:42PM +0100, David Sterba wrote:
>On Wed, Dec 04, 2019 at 05:17:13PM +0900, Naohiro Aota wrote:
>> NODATACOW implies overwriting the file data on a device, which is
>> impossible in sequential required zones. Disable NODATACOW globally with
>> mount option and per-file NODATACOW attribute by masking FS_NOCOW_FL.
>>
>> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
>> ---
>>  fs/btrfs/hmzoned.c | 6 ++++++
>>  fs/btrfs/ioctl.c   | 3 +++
>>  2 files changed, 9 insertions(+)
>>
>> diff --git a/fs/btrfs/hmzoned.c b/fs/btrfs/hmzoned.c
>> index 1c015ed050fc..e890d2ab8cd9 100644
>> --- a/fs/btrfs/hmzoned.c
>> +++ b/fs/btrfs/hmzoned.c
>> @@ -269,5 +269,11 @@ int btrfs_check_mountopts_hmzoned(struct btrfs_fs_info *info)
>>  		return -EINVAL;
>>  	}
>>
>> +	if (btrfs_test_opt(info, NODATACOW)) {
>> +		btrfs_err(info,
>> +		  "cannot enable nodatacow with HMZONED mode");
>> +		return -EINVAL;
>
>That's maybe -EOPNOTSUPP, the error message explains what's wrong and we
>can leave EINVAL for the really invalid arguments. I'll need to look if
>this is consistent with the rest of error code returned from mount
>though.

I'm OK with using -EOPNOTSUPP here in btrfs.

Just for a reference, F2FS returns -EINVAL when it has "nodiscard" or
"mode=adaptive" mount options on zoned block device.