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

[Goffredo Baroncelli <kreijack@inwind.it>]

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)
- 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.

> 
> Josef
BR
G.Baroncelli

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