linux-kernel - Re: linux-next: manual merge of the vfs-brauner tree with the btrfs tree

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Message-ID: <20231129110930.qncvzm63xjg4ucky@quack3>
Date:   Wed, 29 Nov 2023 12:09:30 +0100
From:   Jan Kara <jack@...e.cz>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Christian Brauner <brauner@...nel.org>,
        David Sterba <dsterba@...e.cz>,
        David Sterba <dsterba@...e.com>, Jan Kara <jack@...e.cz>,
        Josef Bacik <josef@...icpanda.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: manual merge of the vfs-brauner tree with the btrfs
 tree

On Tue 28-11-23 14:33:44, Nathan Chancellor wrote:
> Hi Stephen (and other maintainers),
> 
> On Mon, Nov 27, 2023 at 09:20:01AM +1100, Stephen Rothwell wrote:
> > Hi all,
> > 
> > Today's linux-next merge of the vfs-brauner tree got a conflict in:
> > 
> >   fs/btrfs/super.c
> > 
> > between commit:
> > 
> >   2f2cfead5107 ("btrfs: remove old mount API code")
> > 
> > from the btrfs tree and commit:
> > 
> >   ead622674df5 ("btrfs: Do not restrict writes to btrfs devices")
> > 
> > from the vfs-brauner tree.
> > 
> > I fixed it up (the former removed the funtion updated by the latter, but
> > a further fix may be required to implement the intent of the latter?)
> 
> Yes, the lack of ead622674df5 appears to cause issues with mounting
> btrfs volumes on at least next-20231128 due to the presence of commit
> 6f861765464f ("fs: Block writes to mounted block devices"). In QEMU, I
> can see:
> 
>   :: running early hook [udev]
>   Warning: /lib/modules/6.7.0-rc3-next-20231128/modules.devname not found - ignoring
>   Starting systemd-udevd version 252.5-1-arch
>   :: running hook [udev]
>   :: Triggering uevents...
>   :: running hook [keymap]
>   :: Loading keymap...kbd_mode: KDSKBMODE: Inappropriate ioctl for device
>   done.
>   :: performing fsck on '/dev/vda2'
>   :: mounting '/dev/vda2' on real root
>   mount: /new_root: wrong fs type, bad option, bad superblock on /dev/vda2, missing codepage or helper program, or other error.
>          dmesg(1) may have more information after failed mount system call.
>   You are now being dropped into an emergency shell.
>   sh: can't access tty; job control turned off
>   [rootfs ]#
> 
> The following diff allows my VM to boot properly but I am not sure if
> there is a better or more proper fix (I am already out of my element
> heh). If a proper merge solution cannot be found quickly, can
> 6f861765464f be reverted in the meantime so that all my machines with
> btrfs can boot properly? :)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 99d10a25a579..23db0306b8ef 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -299,6 +299,7 @@ static int btrfs_parse_param(struct fs_context *fc,
>  	case Opt_device: {
>  		struct btrfs_device *device;
>  		blk_mode_t mode = sb_open_mode(fc->sb_flags);
> +		mode &= ~BLK_OPEN_RESTRICT_WRITES;
>  
>  		mutex_lock(&uuid_mutex);
>  		device = btrfs_scan_one_device(param->string, mode, false);
> @@ -1801,6 +1802,8 @@ static int btrfs_get_tree_super(struct fs_context *fc)
>  	blk_mode_t mode = sb_open_mode(fc->sb_flags);
>  	int ret;
>  
> +	mode &= ~BLK_OPEN_RESTRICT_WRITES;
> +
>  	btrfs_ctx_to_info(fs_info, ctx);
>  	mutex_lock(&uuid_mutex);

This looks like the proper resolution. Basically btrfs needs to strip
BLK_OPEN_RESTRICT_WRITES from the mode provided by sb_open_mode(). Thanks
for writing it!

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR