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

[Maximiliano Sandoval]

Fiona Ebner <f.ebner at proxmox.com> writes:

> 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.

Requiring the argument to be defined sounds sensible for a helper imo.

> 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/
>

There is the BTRFS_IOC_SET_RECEIVED_SUBVOL ioctl. See [1].

[1] https://btrfs.readthedocs.io/en/latest/btrfs-ioctl.html#overview

>>
>> 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",