[pve-devel] [PATCH storage v4 4/7] btrfs: forcefully set image to readwrite

[Fiona Ebner]

I want to apply the series with a small follow-up, i.e.

>     btrfs: avoid superfluous check in foreach_snapshot_of_subvol() helper
>     
>     The helper iterates with the BTRFS_SNAPSHOT_REGEX regular expression,
>     so there will always be a snapshot name.
>     
>     Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
> ---
>  src/PVE/Storage/BTRFSPlugin.pm | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/src/PVE/Storage/BTRFSPlugin.pm b/src/PVE/Storage/BTRFSPlugin.pm
> index a28996c..e47f25e 100644
> --- a/src/PVE/Storage/BTRFSPlugin.pm
> +++ b/src/PVE/Storage/BTRFSPlugin.pm
> @@ -417,7 +417,6 @@ my sub foreach_snapshot_of_subvol : prototype($$) {
>         my ($volume, $name, $snap_name) = ($1, $2, $3);
>         return if !path_is_subvolume("$dir/$volume");
>         return if $name ne $basename;
> -       return if !defined $snap_name;
>         $code->($snap_name);
>      });
>  }

but I need to ask about this patch first.

Am 19.02.25 um 12:17 schrieb Maximiliano Sandoval:
> When a subvolume is transferred via btrfs send/receive the resulting
> image contains the received_uuid property set. This property is required
> to do incremental snapshots.
> 
> A downside though is that once the received_uuid property is set, it is
> not possible to make the image readwrite again without the force (-f)
> flag, and in such case the received_uuid property is lost. Since we know
> the images are only set to rw for the duration of the move, it is safe
> to set the flag forcefully and then in a future commit add the
> received_uuid property by force.

What do you mean exactly with "add the received_uuid property by force"?
What would the command for that be? Just want to make sure we don't
block our way to support incremental export/import later (it's broken
right now [0], but we might want to implement it at some point).

[0]:
https://lore.proxmox.com/pve-devel/20250221154111.73194-1-f.ebner@proxmox.com/T/

> 
> Signed-off-by: Maximiliano Sandoval <m.sandoval at proxmox.com>
> ---
>  src/PVE/Storage/BTRFSPlugin.pm | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/PVE/Storage/BTRFSPlugin.pm b/src/PVE/Storage/BTRFSPlugin.pm
> index 7dec6e8..9fc51ef 100644
> --- a/src/PVE/Storage/BTRFSPlugin.pm
> +++ b/src/PVE/Storage/BTRFSPlugin.pm
> @@ -895,7 +895,7 @@ sub volume_import {
>  	# Rotate the disk into place, first the current state:
>  	# Note that read-only subvolumes cannot be moved into different directories, but for the
>  	# "current" state we also want a writable copy, so start with that:
> -	$class->btrfs_cmd(['property', 'set', "$tmppath/$diskname\@$snapshot", 'ro', 'false']);
> +	$class->btrfs_cmd(['property', 'set', '-f', "$tmppath/$diskname\@$snapshot", 'ro', 'false']);
>  	PVE::Tools::renameat2(
>  	    -1,
>  	    "$tmppath/$diskname\@$snapshot",
> @@ -917,7 +917,7 @@ sub volume_import {
>  
>  	# Now go through the remaining snapshots (if any)
>  	foreach my $snap (@snapshots) {
> -	    $class->btrfs_cmd(['property', 'set', "$tmppath/$diskname\@$snap", 'ro', 'false']);
> +	    $class->btrfs_cmd(['property', 'set', '-f', "$tmppath/$diskname\@$snap", 'ro', 'false']);
>  	    PVE::Tools::renameat2(
>  		-1,
>  		"$tmppath/$diskname\@$snap",