[pve-devel] [PATCH container v3 1/2] add fsfreeze helper:

[Stoiko Ivanov <s.ivanov@proxmox.com>]

fsfreeze_mountpoint issues the same ioctls as fsfreeze(8) on the provided
directory (the $thaw parameter deciding between '--freeze' and '--unfreeze')

This is used for container backups on RBD, where snapshots on containers,
which are heavy on IO, are not mountable readonly, because the ext4 is not
consistent.

Needed to fix #2991 and #2528.

The ioctl numbers were found via strace -X verbose (and verified with the
kernel documentation).

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
---
 src/PVE/LXC/Config.pm | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/PVE/LXC/Config.pm b/src/PVE/LXC/Config.pm
index 49f599b..0528d51 100644
--- a/src/PVE/LXC/Config.pm
+++ b/src/PVE/LXC/Config.pm
@@ -13,6 +13,9 @@ use PVE::Tools;
 
 use base qw(PVE::AbstractConfig);
 
+use constant {FIFREEZE => 0xc0045877,
+              FITHAW   => 0xc0045878};
+
 my $nodename = PVE::INotify::nodename();
 my $lock_handles =  {};
 my $lockdir = "/run/lock/lxc";
@@ -109,6 +112,22 @@ sub __snapshot_check_freeze_needed {
     return ($ret, $ret);
 }
 
+# implements similar functionality to fsfreeze(8)
+sub fsfreeze_mountpoint {
+    my ($path, $thaw) = @_;
+
+    my $op = $thaw ? 'thaw' : 'freeze';
+    my $ioctl = $thaw ? FITHAW : FIFREEZE;
+
+    sysopen my $fd, $path, O_RDONLY or die "failed to open $path: $!\n";
+    my $ioctl_err;
+    if (!ioctl($fd, $ioctl, 0)) {
+	$ioctl_err = "$!";
+    }
+    close($fd);
+    die "fs$op '$path' failed - $ioctl_err\n" if defined $ioctl_err;
+}
+
 sub __snapshot_freeze {
     my ($class, $vmid, $unfreeze) = @_;
 
-- 
2.20.1