[Libguestfs] [libguestfs PATCH] appliance, daemon: disable lvm2 devicesfile

[Laszlo Ersek]

On 05/30/22 16:23, Richard W.M. Jones wrote:
> On Mon, May 30, 2022 at 04:10:27PM +0200, Laszlo Ersek wrote:
>> 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 at redhat.com>
>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1965941
>> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
>> ---
>>
>> Notes:
>>     Tested:
>>     
>>     - on top of "master" (7afbf5ee4415), using a Fedora 35 host, where the
>>       lvm2 packages copied into the appliance do not have the "devicesfile"
>>       feature (-> regression test);
>>     
>>     - on top of "rhel-9.1" (ad24b9f4d695), in the form of a Brew scratch
>>       build, using a nightly RHEL-9.1 install, where the lvm2 packages
>>       copied into the appliance have the "devicesfile" feature (-> bugfix
>>       test).
>>
>>  daemon/lvm-filter.c | 19 +++++++++++++++++++
>>  appliance/init      | 11 +++++++++++
>>  2 files changed, 30 insertions(+)
>>
>> diff --git a/daemon/lvm-filter.c b/daemon/lvm-filter.c
>> index c6dd35156d37..f75e2198831e 100644
>> --- a/daemon/lvm-filter.c
>> +++ b/daemon/lvm-filter.c
>> @@ -68,6 +68,18 @@ free_lvm_system_dir (void)
>>    free (lvm_system_dir);
>>  }
>>  
>> +static bool devicesfile_feature (void)

Small style fix: I've broken "devicesfile_feature" in the function
definition to a new line.

>> +{
>> +  static bool checked, available;
>> +
>> +  if (!checked) {
>> +    checked = true;
>> +    available = command (NULL, NULL, "lvmdevices", "--help", NULL) == 0 ||
>> +                command (NULL, NULL, "vgimportdevices", "--help", NULL) == 0;
>> +  }
>> +  return available;
>> +}
>> +
>>  /* Rewrite the 'filter = [ ... ]' line in lvm.conf. */
>>  static int
>>  set_filter (char *const *filters)
>> @@ -88,6 +100,13 @@ set_filter (char *const *filters)
>>    }
>>  
>>    fprintf (fp, "devices {\n");
>> +
>> +  /* If lvm2 supports a "devices file", we need to disable its use
>> +   * (RHBZ#1965941).
>> +   */
>> +  if (devicesfile_feature ())
>> +    fprintf (fp, "    use_devicesfile = 0\n");
>> +
>>    for (j = 0; filter_types[j] != NULL; ++j) {
>>      fprintf (fp, "    %s = [\n", filter_types[j]);
>>      fprintf (fp, "        ");
>> diff --git a/appliance/init b/appliance/init
>> index 7076821d2250..19aa151b73aa 100755
>> --- a/appliance/init
>> +++ b/appliance/init
>> @@ -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
>>
>> base-commit: 7afbf5ee4415f6fa2553898d3af238e794062096
>> -- 
>> 2.19.1.3.g30247aa5d201
> 
> Looks reasonable to me, so:
> 
> Acked-by: Richard W.M. Jones <rjones at redhat.com>

Commit 8fc4d167153a.

Thanks!
Laszlo