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Date:   Thu, 6 Jan 2022 16:03:34 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc:     Sahil Kang <sahil.kang@asilaycomputing.com>,
        linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 1/1] btrfs: reuse existing pointers from btrfs_ioctl
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On Wed, Jan 05, 2022 at 05:53:20PM +0800, Qu Wenruo wrote:
> One suspicious ioctls, they should require write permission, but don't:
> 
> - btrfs_ioctl_start_sync()
>    If there is no running trans, it would bail out without doing
>    anything, but I'm wondering if we should call mnt_want_write_file().
> 
>    As this means, if we mount a subvolume read-only, but the fs still has
>    some part mounted RW, we can start a sync using the read-only mounted
>    part.

We can possibly do the mnt_want_write but it should not propagate the
errors, because calling sync on a fully read-only filesystem should not
error out.