Re: [RFC PATCH 2/3] btrfs-progs: kernel based default features for mkfs

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

Thanks Jeff for the comments.

On 10/23/2015 11:24 PM, Jeff Mahoney wrote:
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> On 10/21/15 4:45 AM, Anand Jain wrote:
>> mkfs from latest btrfs-progs will enable latest default features,
>> and if the kernel is down-rev and does not support a latest
>> default feature then mount fails, as expected.
>>
>> This patch disables default features based on the running kernel.
>
> I like the idea generally based on comments further in the thread, but
> what I don't like is:
>
> 1) It's silent.

  Will add warning.

> 2) There's no way to override it.

> If we're going to change the defaults at runtime, we should tell the
> user what has changed and why.  Otherwise, an identical mkfs.btrfs
> binary will behave differently on different systems without feedback
> and that violates the principle of least surprise.  If they want to do
> what Qu suggests later in the thread, where the device is being
> prepared for use on a newer kernel, it should be possible to force it.
>   The normal -f should be fine there.

  Sill have no idea how to get this, trying.

Thanks, Anand


> - -Jeff
>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com> --- mkfs.c | 5
>> ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mkfs.c b/mkfs.c index a5802f7..2b9d734 100644 ---
>> a/mkfs.c +++ b/mkfs.c @@ -1357,10 +1357,13 @@ int main(int ac, char
>> **av) int dev_cnt = 0; int saved_optind; char
>> fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 }; -	u64 features =
>> BTRFS_MKFS_DEFAULT_FEATURES; +	u64 features; struct mkfs_allocation
>> allocation = { 0 }; struct btrfs_mkfs_config mkfs_cfg;
>>
>> +	features = btrfs_features_allowed_by_kernel(); +	features &=
>> BTRFS_MKFS_DEFAULT_FEATURES; + while(1) { int c; static const
>> struct option long_options[] = {
>>
>
>
> - --
> Jeff Mahoney
> SUSE Labs
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