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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2019 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package main
import (
"github.com/snapcore/snapd/logger"
"github.com/snapcore/snapd/osutil"
)
// MountProfileUpdateContext provides the context of a mount namespace update.
// The context provides a way to synchronize the operation with other users of
// the snap system, to load and save the mount profiles and to provide the file
// system assumptions with which the mount namespace will be modified.
type MountProfileUpdateContext interface {
// Lock obtains locks appropriate for the update.
Lock() (unlock func(), err error)
// Assumptions computes filesystem assumptions under which the update shall operate.
Assumptions() *Assumptions
// LoadDesiredProfile loads the mount profile that should be constructed.
LoadDesiredProfile() (*osutil.MountProfile, error)
// LoadCurrentProfile loads the mount profile that is currently applied.
LoadCurrentProfile() (*osutil.MountProfile, error)
// SaveCurrentProfile saves the mount profile that is currently applied.
SaveCurrentProfile(*osutil.MountProfile) error
}
func executeMountProfileUpdate(upCtx MountProfileUpdateContext) error {
unlock, err := upCtx.Lock()
if err != nil {
return err
}
defer unlock()
desired, err := upCtx.LoadDesiredProfile()
if err != nil {
return err
}
currentBefore, err := upCtx.LoadCurrentProfile()
if err != nil {
return err
}
// Synthesize mount changes that were applied before for the purpose of the tmpfs detector.
as := upCtx.Assumptions()
for _, entry := range currentBefore.Entries {
as.AddChange(&Change{Action: Mount, Entry: entry})
}
// Compute the needed changes and perform each change if
// needed, collecting those that we managed to perform or that
// were performed already.
changesNeeded := NeededChanges(currentBefore, desired)
var changesMade []*Change
for _, change := range changesNeeded {
synthesised, err := change.Perform(as)
changesMade = append(changesMade, synthesised...)
if err != nil {
// We may have done something even if Perform itself has
// failed. We need to collect synthesized changes and
// store them.
origin := change.Entry.XSnapdOrigin()
if origin == "layout" || origin == "overname" {
// TODO: convert the test to a method over origin.
return err
} else if err != ErrIgnoredMissingMount {
logger.Noticef("cannot change mount namespace according to change %s: %s", change, err)
}
continue
}
changesMade = append(changesMade, change)
}
// Compute the new current profile so that it contains only changes that were made
// and save it back for next runs.
currentAfter := CurrentProfileFromChangesMade(changesMade)
return upCtx.SaveCurrentProfile(¤tAfter)
}
// CurrentProfileFromChangesMade computes a new mount profile a slice of changes.
//
// The return value collects mount profile entries from changes of type "mount"
// and "keep" while discarding the changes of type "unmount". The order in
// which entries are collected depends on their type.
//
// The sequence of changes, as produced by NeededChanges, is computed by
// looking at two mount profiles, examining the most recent change and working
// backwards. Since the most recent change is the last entry in the mount
// profile, the first change describes the last mount entry of the old mount
// profile.
//
// The "keep" changes are thus collected in reverse order - the order of their
// true appearance, while "mount" changes are collected in the order of their
// appearance as this represents the actual order of performed mount
// operations.
func CurrentProfileFromChangesMade(changes []*Change) osutil.MountProfile {
var profile osutil.MountProfile
for i := len(changes) - 1; i >= 0; i-- {
change := changes[i]
if change.Action == Keep {
profile.Entries = append(profile.Entries, change.Entry)
}
}
for _, change := range changes {
if change.Action == Mount {
profile.Entries = append(profile.Entries, change.Entry)
}
}
return profile
}
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