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appliance, daemon: disable lvm2 devicesfile

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In guestfs-tools commit 4fe8a03cd2d3 ('sysprep: remove lvm2's default
"system.devices" file', 2022-04-11), we disabled the use of LVM2's new
"devicesfile" feature, which could interfere with the cloning of virtual
machines.

We suspected in

  https://bugzilla.redhat.com/show_bug.cgi?id=2072493#c6

that the same lvm2 feature could affect the libguestfs appliance itself,
but decided in

  https://bugzilla.redhat.com/show_bug.cgi?id=2072493#c8
  https://bugzilla.redhat.com/show_bug.cgi?id=2072493#c10

that this would not be the case, because "appliance/init" already
constructed a pristine LVM_SYSTEM_DIR.

Unfortunately, that's not enough: due to the "use_devicesfile=1" default
(on RHEL9 anyway), some "lvm" invocation, possibly inside the
lvm-set-filter API, *creates* "$LVM_SYSTEM_DIR/devices/system.devices".
And then we get (minimally) warnings such as

> Please remove the lvm.conf global_filter, it is ignored with the devices
> file.
> Please remove the lvm.conf filter, it is ignored with the devices file.

when using the lvm-set-filter API.

Explicitly disable the "devices file" in "appliance/init", and also
whenever we rewrite "lvm.conf" -- that is, in set_filter()
[daemon/lvm-filter.c]. In the former, check for the feature by locating
the devicesfile-related utilities "lvmdevices" and "vgimportdevices". In
the C code, invoke the utilities with the "--help" option instead. (In
"appliance/init",  I thought it was best not to call any lvm2 utilities
even with "--help", with our lvm2.conf still under construction there.) If
either utility is available, set "use_devicesfile = 0".

Cc: David Teigland <teigland@redhat.com>
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1965941
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20220530141027.16167-1-lersek@redhat.com>
Acked-by: Richard W.M. Jones <rjones@redhat.com>
[lersek@redhat.com: style fix: break "devicesfile_feature" in the function
 definition to a new line]
This commit is contained in:
Laszlo Ersek
2022-05-30 16:10:27 +02:00
parent 7afbf5ee44
commit 8fc4d16715
2 changed files with 31 additions and 0 deletions
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11
appliance/init
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@@ -134,6 +134,17 @@ mdadm -As --auto=yes --no-degraded
# Empty LVM configuration file means "all defaults".
mkdir -p /tmp/lvm
touch /tmp/lvm/lvm.conf
# If lvm2 supports a "devices file", we need to disable its use
# (RHBZ#1965941).
if command -v lvmdevices || command -v vgimportdevices; then
{
printf 'devices {\n'
printf '\tuse_devicesfile = 0\n'
printf '}\n'
} >> /tmp/lvm/lvm.conf
fi
LVM_SYSTEM_DIR=/tmp/lvm
export LVM_SYSTEM_DIR
lvmetad