Re: [PATCH 0/7] Let user specify the kernel version for features

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Anand Jain wrote on 2015/11/25 20:08 +0800:
> Sometimes users may want to have a btrfs to be supported on multiple
> kernel version. A simple example, USB drive can be used with multiple
> system running different kernel versions. Or in a data center a SAN
> LUN could be mounted on any system with different kernel version.
>
> Thanks for providing comments and feedback.
> Further to it, here below is a set of patch which will introduce, to
> specify a kernel version so that default features can be set based on
> what features were supported at that kernel version.

With the new -O comp= option, the concern on user who want to make a 
btrfs for newer kernel is hugely reduced.

But I still prefer such feature align to be done only when specified by 
user, instead of automatically. (yeah, already told for several times 
though)
Warning should be enough for user, sometimes too automatic is not  good, 
especially for tests.

A lot of btrfs-progs change, like recent disabling mixed-bg for small 
volume has already cause regression in generic/077 testcase.
And Dave is already fed up with such problem from btrfs...

Especially such auto-detection will make default behavior more unstable, 
at least not a good idea for me.



Beside this, I'm curious how other filesystm user tools handle such 
kernel mismatch, or do they?

Thanks,
Qu


>
> First of all to let user know what features was supported at what kernel
> version. Patch 1/7 updates -O list-all which will list the feature with
> version.
>
> As we didn't maintain the sysfs and progs feature names consistent, so
> to avoid confusion Patch 2/7 displays sysfs feature name as well again
> in the list-all output.
>
> Next, Patch 3,4,5/7 are helper functions.
>
> Patch 6,7/7 provides the -O comp=<version> for mkfs.btrfs and
> btrfs-convert respectively
>
> Thanks, Anand
>
> Anand Jain (7):
>    btrfs-progs: show the version for -O list-all
>    btrfs-progs: add kernel alias for each of the features in the list
>    btrfs-progs: make is_numerical non static
>    btrfs-progs: check for numerical in version_to_code()
>    btrfs-progs: introduce framework version to features
>    btrfs-progs: add -O comp= option for mkfs.btrfs
>    btrfs-progs: add -O comp= option for btrfs-convert
>
>   btrfs-convert.c | 21 +++++++++++++++++++++
>   cmds-replace.c  | 11 -----------
>   mkfs.c          | 24 ++++++++++++++++++++++--
>   utils.c         | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++-----
>   utils.h         |  2 ++
>   5 files changed, 98 insertions(+), 18 deletions(-)
>