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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2023 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 sysparams
import (
"bufio"
"fmt"
"os"
"strings"
"github.com/snapcore/snapd/dirs"
"github.com/snapcore/snapd/osutil"
)
// For mocking in tests
var (
osutilAtomicWriteFile = osutil.AtomicWriteFile
)
// SystemParams manages certain system configuration parameters
// aspects like the homedirs configuration that must be available
// for other binaries, as snap-confine.
type SystemParams struct {
// rootdir is stored to allow for updating the same
// system-params file.
rootdir string
// Homedirs is the comma-delimited list of user specified home
// directories that should be mounted.
Homedirs string
}
func parseSystemParams(contents string) (*SystemParams, error) {
params := &SystemParams{}
seen := make(map[string]bool)
scanner := bufio.NewScanner(strings.NewReader(contents))
for scanner.Scan() {
line := scanner.Text()
// ignore empty lines and comments
if len(line) == 0 || strings.HasPrefix(line, "#") {
continue
}
tokens := strings.SplitN(line, "=", 2)
if len(tokens) != 2 {
return nil, fmt.Errorf("invalid line: %q", line)
}
// ensure that each configuration value only appears once
if ok := seen[tokens[0]]; ok {
return nil, fmt.Errorf("duplicate entry found: %q", tokens[0])
}
seen[tokens[0]] = true
if tokens[0] == "homedirs" {
params.Homedirs = tokens[1]
} else {
return nil, fmt.Errorf("invalid line: %q", line)
}
}
if err := scanner.Err(); err != nil {
return nil, err
}
return params, nil
}
func sysparamsFile(rootdir string) string {
if rootdir == "" {
rootdir = dirs.GlobalRootDir
}
return dirs.SnapSystemParamsUnder(rootdir)
}
// Open either reads the existing file at <rootdir>/var/lib/snapd/system-params
// or in case the file does not exist, it will initialize and return a
// new SystemParams structure.
func Open(rootdir string) (*SystemParams, error) {
sspFile := sysparamsFile(rootdir)
if !osutil.FileExists(sspFile) {
return &SystemParams{rootdir: rootdir}, nil
}
data, err := os.ReadFile(sspFile)
if err != nil {
return nil, fmt.Errorf("cannot read system-params: %v", err)
}
params, err := parseSystemParams(string(data))
if err != nil {
return nil, fmt.Errorf("cannot parse system-params: %v", err)
}
params.rootdir = rootdir
return params, nil
}
// Write updates the system-params file with the values in the
// SystemParams instance.
func (ssp *SystemParams) Write() error {
sspFile := sysparamsFile(ssp.rootdir)
contents := fmt.Sprintf("homedirs=%s\n", ssp.Homedirs)
if err := osutilAtomicWriteFile(sspFile, []byte(contents), 0644, 0); err != nil {
return fmt.Errorf("cannot write system-params: %v", err)
}
return nil
}
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