github.com/david-imola/snapd@v0.0.0-20210611180407-2de8ddeece6d/overlord/snapstate/policy/policy.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2019 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  // Package policy implements fine grained decision-making for snapstate
    21  package policy
    22  
    23  import (
    24  	"github.com/snapcore/snapd/asserts"
    25  	"github.com/snapcore/snapd/boot"
    26  	"github.com/snapcore/snapd/overlord/snapstate"
    27  	"github.com/snapcore/snapd/overlord/state"
    28  	"github.com/snapcore/snapd/snap"
    29  )
    30  
    31  func init() {
    32  	snapstate.PolicyFor = For
    33  }
    34  
    35  func For(typ snap.Type, model *asserts.Model) snapstate.Policy {
    36  	switch typ {
    37  	case snap.TypeKernel:
    38  		return &kernelPolicy{modelKernel: model.Kernel()}
    39  	case snap.TypeGadget:
    40  		return &gadgetPolicy{modelGadget: model.Gadget()}
    41  	case snap.TypeOS:
    42  		return &osPolicy{modelBase: model.Base()}
    43  	case snap.TypeBase:
    44  		return &basePolicy{modelBase: model.Base()}
    45  	case snap.TypeSnapd:
    46  		return &snapdPolicy{onClassic: model.Classic()}
    47  	default:
    48  		return appPolicy{}
    49  	}
    50  }
    51  
    52  func ephemeral(dev boot.Device) bool {
    53  	return !dev.RunMode()
    54  }
    55  
    56  func inUse(name string, rev snap.Revision, typ snap.Type, dev boot.Device) error {
    57  	check, err := boot.InUse(typ, dev)
    58  	if err != nil {
    59  		return err
    60  	}
    61  	if check(name, rev) {
    62  		return errInUseForBoot
    63  	}
    64  	return nil
    65  }
    66  
    67  type appPolicy struct{}
    68  
    69  func (appPolicy) CanRemove(_ *state.State, snapst *snapstate.SnapState, rev snap.Revision, dev boot.Device) error {
    70  	if ephemeral(dev) {
    71  		return errEphemeralSnapsNotRemovalable
    72  	}
    73  
    74  	if !rev.Unset() {
    75  		return nil
    76  	}
    77  
    78  	if snapst.Required {
    79  		return errRequired
    80  	}
    81  
    82  	return nil
    83  }