From bf360289677ef0dfd80cadfa736e6cde40f8a3b8 Mon Sep 17 00:00:00 2001
From: Axel Burri <axel@tty0.ch>
Date: Wed, 19 Oct 2022 13:04:35 +0200
Subject: [PATCH] WIP btrbk: run btrfs commands with ionice

Add `ionice` command in front of all btrfs commands if either
`ionice_class` or `ionice_level` is set.

KNOWN BUGS:

 - puts `ionice` in front of sudo if backend=btrbk-progs-sudo is set.

 - probably makes only sense for `btrfs send` and `btrfs receive`
   operations.

Example:

    target send-receive /tmp/btrbk/mnt_target/
      ionice_class 1
      ionice_level 0
---
 btrbk | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/btrbk b/btrbk
index f34dca7..17a8541 100755
--- a/btrbk
+++ b/btrbk
@@ -140,6 +140,13 @@ my %config_options = (
   backend_remote              => { default => undef,         accept => [qw( no btrfs-progs btrfs-progs-btrbk btrfs-progs-sudo btrfs-progs-doas )] },
   backend_local_user          => { default => undef,         accept => [qw( no btrfs-progs btrfs-progs-btrbk btrfs-progs-sudo btrfs-progs-doas )] },
 
+  ionice_class                => { default => undef,         accept => [ qw( no ), (0..3) ] },
+  ionice_class_local          => { default => undef,         accept => [ qw( no ), (0..3) ] },
+  ionice_class_remote         => { default => undef,         accept => [ qw( no ), (0..3) ] },
+  ionice_level                => { default => undef,         accept => [ qw( no ), (0..7) ] },
+  ionice_level_local          => { default => undef,         accept => [ qw( no ), (0..7) ] },
+  ionice_level_remote         => { default => undef,         accept => [ qw( no ), (0..7) ] },
+
   compat                      => { default => undef,         accept => [qw( no busybox ignore_receive_errors )], split => 1 },
   compat_local                => { default => undef,         accept => [qw( no busybox ignore_receive_errors )], split => 1 },
   compat_remote               => { default => undef,         accept => [qw( no busybox ignore_receive_errors )], split => 1 },
@@ -2758,7 +2765,14 @@ sub vinfo_cmd($$@)
   my @cmd_args = @_;
   my $backend = config_key_lru($vinfo, "backend") // die;
   my $cmd_mapped = $backend_cmd_map{$backend}{$cmd} // [ split(" ", $cmd) ];
-  return [ @$cmd_mapped, @cmd_args ];
+  my @ionice;
+  my $ionice_class = config_key_lru($vinfo, "ionice_class");
+  my $ionice_level = config_key_lru($vinfo, "ionice_level");
+  push @ionice, "-c", $ionice_class if $ionice_class;
+  push @ionice, "-n", $ionice_level if $ionice_level;
+  unshift @ionice, "ionice" if @ionice;
+
+  return [ @ionice, @$cmd_mapped, @cmd_args ];
 }
 
 sub _get_btrbk_date(@)