Re: [PATCH 0/7][V11] btrfs: allocation_hint

[Josef Bacik <josef@toxicpanda.com>]

On Thu, Mar 03, 2022 at 08:01:00PM +0100, Goffredo Baroncelli wrote:
> On 02/03/2022 22.23, Josef Bacik wrote:
> > On Wed, Mar 02, 2022 at 08:30:22PM +0100, Goffredo Baroncelli wrote:
> [...]
> > > 
> > > For simple filesystem (e.g. 1 disk), it is trivial (and not useful); for more complex
> > > one (2, 3 disks) it is easy to make mistake.
> > > 
> > > btrfs-progs relies on major_minor; it is possible to used the BTRFS_IOC_DEV_INFO
> > > but it requires CAP_ADMIN....
> > > 
> > 
> > Well this just made me go look at the code and realize you don't require
> > CAP_ADMIN for the sysfs knob, which we're going to need.  So using
> > BTRFS_IOC_DEV_INFO shouldn't be a problem.  Thanks,
> 
> I am not sure to be understood completely your answer, so I recap what I am doing:
> - replace the "int" interface in favor of a "string" interface (not "echo 123 > allocaton_hint"
>   but "echo DATA_ONLY > allocaton_hint") [DONE]
> - remove the "kernel" patch related to "major_minor" [DONE]
> - update the btrfs-progs patch to use BTRFS_IOC_DEV_INFO instead of <devid>/major_minor [WIP]
> 
> 
> This will have the following consequences:
> - any user is still capable to read <devid>/allocaton_hint
> - only root is able to use "btrfs prop get allocaton_hint <devname>" (before any user)

Ah yeah I see how this is annoying, oh well it can't be helped.

> - only root is able to update <devid>/allocaton_hint
> - only root is able to use "btrfs prop set allocation_hint <devname>"
> 
> The 2nd point may be relaxed allowing to use BTRFS_IOC_DEV_INFO even to not root user (
> I don't think that there is any sensitive data exported by BTRFS_IOC_DEV_INFO); but this will
> be done as separate patch.

Agreed, I think that's a reasonable thing, and yes separately please.

This is all good, thanks Goffredo!

Josef