github.com/chipaca/snappy@v0.0.0-20210104084008-1f06296fe8ad/gadget/install/content.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2019-2020 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 install
    21  
    22  import (
    23  	"fmt"
    24  	"os"
    25  	"path/filepath"
    26  	"strconv"
    27  
    28  	"github.com/snapcore/snapd/dirs"
    29  	"github.com/snapcore/snapd/gadget"
    30  	"github.com/snapcore/snapd/gadget/internal"
    31  	"github.com/snapcore/snapd/logger"
    32  )
    33  
    34  var contentMountpoint string
    35  
    36  func init() {
    37  	contentMountpoint = filepath.Join(dirs.SnapRunDir, "gadget-install")
    38  }
    39  
    40  // makeFilesystem creates a filesystem on the on-disk structure, according
    41  // to the filesystem type defined in the gadget.
    42  func makeFilesystem(ds *gadget.OnDiskStructure) error {
    43  	if ds.HasFilesystem() {
    44  		logger.Debugf("create %s filesystem on %s with label %q", ds.VolumeStructure.Filesystem, ds.Node, ds.VolumeStructure.Label)
    45  		if err := internal.Mkfs(ds.VolumeStructure.Filesystem, ds.Node, ds.VolumeStructure.Label, ds.Size); err != nil {
    46  			return err
    47  		}
    48  		if err := udevTrigger(ds.Node); err != nil {
    49  			return err
    50  		}
    51  	}
    52  	return nil
    53  }
    54  
    55  // writeContent populates the given on-disk structure, according to the contents
    56  // defined in the gadget.
    57  func writeContent(ds *gadget.OnDiskStructure, gadgetRoot string, observer gadget.ContentObserver) error {
    58  	switch {
    59  	case !ds.IsPartition():
    60  		return fmt.Errorf("cannot write non-partitions yet")
    61  	case !ds.HasFilesystem():
    62  		if err := writeNonFSContent(ds, gadgetRoot); err != nil {
    63  			return err
    64  		}
    65  	case ds.HasFilesystem():
    66  		if err := writeFilesystemContent(ds, gadgetRoot, observer); err != nil {
    67  			return err
    68  		}
    69  	}
    70  
    71  	return nil
    72  }
    73  
    74  // mountFilesystem mounts the on-disk structure filesystem under the given base
    75  // directory, using the label defined in the gadget as the mount point name.
    76  func mountFilesystem(ds *gadget.OnDiskStructure, baseMntPoint string) error {
    77  	if !ds.HasFilesystem() {
    78  		return fmt.Errorf("cannot mount a partition with no filesystem")
    79  	}
    80  	if ds.Label == "" {
    81  		return fmt.Errorf("cannot mount a filesystem with no label")
    82  	}
    83  
    84  	mountpoint := filepath.Join(baseMntPoint, ds.Label)
    85  	if err := os.MkdirAll(mountpoint, 0755); err != nil {
    86  		return fmt.Errorf("cannot create mountpoint: %v", err)
    87  	}
    88  	if err := sysMount(ds.Node, mountpoint, ds.Filesystem, 0, ""); err != nil {
    89  		return fmt.Errorf("cannot mount filesystem %q at %q: %v", ds.Node, mountpoint, err)
    90  	}
    91  
    92  	return nil
    93  }
    94  
    95  func writeFilesystemContent(ds *gadget.OnDiskStructure, gadgetRoot string, observer gadget.ContentObserver) (err error) {
    96  	mountpoint := filepath.Join(contentMountpoint, strconv.Itoa(ds.Index))
    97  	if err := os.MkdirAll(mountpoint, 0755); err != nil {
    98  		return err
    99  	}
   100  
   101  	// temporarily mount the filesystem
   102  	if err := sysMount(ds.Node, mountpoint, ds.Filesystem, 0, ""); err != nil {
   103  		return fmt.Errorf("cannot mount filesystem %q at %q: %v", ds.Node, mountpoint, err)
   104  	}
   105  	defer func() {
   106  		errUnmount := sysUnmount(mountpoint, 0)
   107  		if err == nil {
   108  			err = errUnmount
   109  		}
   110  	}()
   111  	fs, err := gadget.NewMountedFilesystemWriter(gadgetRoot, &ds.LaidOutStructure, observer)
   112  	if err != nil {
   113  		return fmt.Errorf("cannot create filesystem image writer: %v", err)
   114  	}
   115  
   116  	var noFilesToPreserve []string
   117  	if err := fs.Write(mountpoint, noFilesToPreserve); err != nil {
   118  		return fmt.Errorf("cannot create filesystem image: %v", err)
   119  	}
   120  
   121  	return nil
   122  }
   123  
   124  func writeNonFSContent(ds *gadget.OnDiskStructure, gadgetRoot string) error {
   125  	f, err := os.OpenFile(ds.Node, os.O_RDWR, 0644)
   126  	if err != nil {
   127  		return fmt.Errorf("cannot write bare content for %q: %v", ds.Node, err)
   128  	}
   129  	defer f.Close()
   130  
   131  	// Laid out structures start relative to the beginning of the
   132  	// volume, shift the structure offsets to 0, so that it starts
   133  	// at the beginning of the partition
   134  	l := gadget.ShiftStructureTo(ds.LaidOutStructure, 0)
   135  	raw, err := gadget.NewRawStructureWriter(gadgetRoot, &l)
   136  	if err != nil {
   137  		return err
   138  	}
   139  	return raw.Write(f)
   140  }