github.com/stolowski/snapd@v0.0.0-20210407085831-115137ce5a22/osutil/mountprofile_linux.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2017 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 osutil
    21  
    22  import (
    23  	"bufio"
    24  	"bytes"
    25  	"fmt"
    26  	"io"
    27  	"os"
    28  	"strings"
    29  )
    30  
    31  // MountProfile represents an array of mount entries.
    32  type MountProfile struct {
    33  	Entries []MountEntry
    34  }
    35  
    36  // LoadMountProfile loads a mount profile from a given file.
    37  //
    38  // The file may be absent, in such case an empty profile is returned without errors.
    39  func LoadMountProfile(fname string) (*MountProfile, error) {
    40  	f, err := os.Open(fname)
    41  	if err != nil && os.IsNotExist(err) {
    42  		return &MountProfile{}, nil
    43  	}
    44  	if err != nil {
    45  		return nil, err
    46  	}
    47  	defer f.Close()
    48  	return ReadMountProfile(f)
    49  }
    50  
    51  // LoadMountProfileText loads a mount profile from a given string.
    52  func LoadMountProfileText(fstab string) (*MountProfile, error) {
    53  	return ReadMountProfile(strings.NewReader(fstab))
    54  }
    55  
    56  func SaveMountProfileText(p *MountProfile) (string, error) {
    57  	var buf bytes.Buffer
    58  	_, err := p.WriteTo(&buf)
    59  	if err != nil {
    60  		return "", err
    61  	}
    62  	return buf.String(), nil
    63  }
    64  
    65  // Save saves a mount profile (fstab-like) to a given file.
    66  // The profile is saved with an atomic write+rename+sync operation.
    67  func (p *MountProfile) Save(fname string) error {
    68  	var buf bytes.Buffer
    69  	if _, err := p.WriteTo(&buf); err != nil {
    70  		return err
    71  	}
    72  	return AtomicWriteFile(fname, buf.Bytes(), 0644, AtomicWriteFlags(0))
    73  }
    74  
    75  // ReadMountProfile reads and parses a mount profile.
    76  //
    77  // The supported format is described by fstab(5).
    78  func ReadMountProfile(reader io.Reader) (*MountProfile, error) {
    79  	var p MountProfile
    80  	scanner := bufio.NewScanner(reader)
    81  	for scanner.Scan() {
    82  		s := scanner.Text()
    83  		s = strings.TrimSpace(s)
    84  		// Skip lines that only contain a comment, that is, those that start
    85  		// with the '#' character (ignoring leading spaces). This specifically
    86  		// allows us to parse '#' inside individual fields, which the fstab(5)
    87  		// specification allows.
    88  		if strings.IndexByte(s, '#') == 0 {
    89  			continue
    90  		}
    91  		// Skip lines that are totally empty
    92  		if s == "" {
    93  			continue
    94  		}
    95  		entry, err := ParseMountEntry(s)
    96  		if err != nil {
    97  			return nil, err
    98  		}
    99  		p.Entries = append(p.Entries, entry)
   100  	}
   101  	if err := scanner.Err(); err != nil {
   102  		return nil, err
   103  	}
   104  	return &p, nil
   105  }
   106  
   107  // WriteTo writes a mount profile to the given writer.
   108  //
   109  // The supported format is described by fstab(5).
   110  // Note that there is no support for comments.
   111  func (p *MountProfile) WriteTo(writer io.Writer) (int64, error) {
   112  	var written int64
   113  	for i := range p.Entries {
   114  		var n int
   115  		var err error
   116  		if n, err = fmt.Fprintf(writer, "%s\n", p.Entries[i]); err != nil {
   117  			return written, err
   118  		}
   119  		written += int64(n)
   120  	}
   121  	return written, nil
   122  }