Merge pull request #26695 from poettering/dissect-mount-helper

make "systemd-dissect --mount" available as /sbin/mount.ddi
2023-03-07 20:07:17 +00:00
parent 1a87882635 92828ba603
commit ce0cac4c8e
5 changed files with 136 additions and 4 deletions
@@ -902,7 +902,7 @@ manpages = [
 ['systemd-debug-generator', '8', [], ''],
 ['systemd-delta', '1', [], ''],
 ['systemd-detect-virt', '1', [], ''],
- ['systemd-dissect', '1', [], 'HAVE_BLKID'],
+ ['systemd-dissect', '1', ['mount.ddi'], 'HAVE_BLKID'],
 ['systemd-environment-d-generator',
  '8',
  ['30-systemd-environment-d-generator'],
@@ -18,6 +18,7 @@

  <refnamediv>
    <refname>systemd-dissect</refname>
+    <refname>mount.ddi</refname>
    <refpurpose>Dissect Discoverable Disk Images (DDIs)</refpurpose>
  </refnamediv>

@@ -99,6 +100,14 @@
    what it operates with when mounting the image. To display the complete list of partitions use a tool such
    as <citerefentry
    project='man-pages'><refentrytitle>fdisk</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
+
+    <para>The <command>systemd-dissect</command> command may be invoked as <command>mount.ddi</command> in
+    which case it implements the <citerefentry
+    project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry> "external
+    helper" interface. This ensures disk images compatible with <command>systemd-dissect</command> can be
+    mounted directly by <command>mount</command> and <citerefentry
+    project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. For
+    details see below.</para>
  </refsect1>

  <refsect1>
@@ -132,7 +141,13 @@
        <para>All mounted file systems are checked with the appropriate <citerefentry
        project='man-pages'><refentrytitle>fsck</refentrytitle><manvolnum>8</manvolnum></citerefentry>
        implementation in automatic fixing mode, unless explicitly turned off (<option>--fsck=no</option>) or
-        read-only operation is requested (<option>--read-only</option>).</para></listitem>
+        read-only operation is requested (<option>--read-only</option>).</para>
+
+        <para>Note that this functionality is also available in <citerefentry
+        project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry> via a
+        command such as <command>mount -t ddi myimage.raw targetdir/</command>, as well as in <citerefentry
+        project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. For
+        details, see below.</para></listitem>
      </varlistentry>

      <varlistentry>
@@ -359,6 +374,35 @@
    command is used the exit status of the invoked command is propagated.</para>
  </refsect1>

+  <refsect1>
+    <title>Invocation as <command>/sbin/mount.ddi</command></title>
+
+    <para>The <command>systemd-dissect</command> executable may be symlinked to
+    <filename>/sbin/mount.ddi</filename>. If invoked through that it implements <citerefentry
+    project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
+    "external helper" interface for the (pseudo) file system type <literal>ddi</literal>. This means
+    conformant disk images may be mounted directly via</para>
+
+    <programlisting># mount -t ddi myimage.raw targetdir/</programlisting>
+
+    <para>in a fashion mostly equivalent to:</para>
+
+    <programlisting># systemd-dissect --mount myimage.raw targetdir/</programlisting>
+
+    <para>Note that since a single DDI may contain multiple file systems it should later be unmounted with
+    <command>umount -R targetdir/</command>, for recursive operation.</para>
+
+    <para>This functionality is particularly useful to mount DDIs automatically at boot via simple
+    <filename>/etc/fstab</filename> entries. For example:</para>
+
+    <programlisting>/path/to/myimage.raw /images/myimage/ ddi defaults 0 0</programlisting>
+
+    <para>When invoked this way the mount options <literal>ro</literal>, <literal>rw</literal>,
+    <literal>discard</literal>, <literal>nodiscard</literal> map to the corresponding options listed above
+    (i.e. <option>--read-only</option>, <option>--discard=all</option>,
+    <option>--discard=disabled</option>). Mount options are <emphasis>not</emphasis> generically passed on to
+    the file systems inside the images.</para>
+  </refsect1>

  <refsect1>
    <title>Examples</title>
@@ -366,7 +410,7 @@
    <example>
      <title>Generate a tarball from an OS disk image</title>

-      <programlisting>$ systemd-dissect --with foo.raw tar cz . >foo.tar.gz</programlisting>
+      <programlisting># systemd-dissect --with foo.raw tar cz . >foo.tar.gz</programlisting>
    </example>
  </refsect1>

@@ -377,6 +421,7 @@
      <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>,
+      <citerefentry project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>umount</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>fdisk</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
@@ -2478,6 +2478,10 @@ if conf.get('HAVE_BLKID') == 1
                dependencies : [versiondep],
                install_rpath : rootpkglibdir,
                install : true)
+
+        meson.add_install_script(meson_make_symlink,
+                                 bindir / 'systemd-dissect',
+                                 rootsbindir / 'mount.ddi')
 endif

 if conf.get('ENABLE_RESOLVE') == 1
@@ -522,6 +522,80 @@ static int parse_argv(int argc, char *argv[]) {
        return 1;
 }

+static int parse_argv_as_mount_helper(int argc, char *argv[]) {
+        const char *options = NULL;
+        bool fake = false;
+        int c, r;
+
+        /* Implements util-linux "external helper" command line interface, as per mount(8) man page. */
+
+        while ((c = getopt(argc, argv, "sfnvN:o:t:")) >= 0) {
+                switch(c) {
+
+                case 'f':
+                        fake = true;
+                        break;
+
+                case 'o':
+                        options = optarg;
+                        break;
+
+                case 't':
+                        if (!streq(optarg, "ddi"))
+                                log_debug("Unexpected file system type '%s', ignoring.", optarg);
+                        break;
+
+                case 's': /* sloppy mount options */
+                case 'n': /* aka --no-mtab */
+                case 'v': /* aka --verbose */
+                        log_debug("Ignoring option -%c, not implemented.", c);
+                        break;
+
+                case 'N': /* aka --namespace= */
+                        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Option -%c is not implemented, refusing.", c);
+
+                case '?':
+                        return -EINVAL;
+                }
+        }
+
+        if (optind + 2 != argc)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "Expected an image file path and target directory as only argument.");
+
+        for (const char *p = options;;) {
+                _cleanup_free_ char *word = NULL;
+
+                r = extract_first_word(&p, &word, ",", EXTRACT_KEEP_QUOTE);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to extract mount option: %m");
+                if (r == 0)
+                        break;
+
+                if (streq(word, "ro"))
+                        SET_FLAG(arg_flags, DISSECT_IMAGE_READ_ONLY, true);
+                else if (streq(word, "rw"))
+                        SET_FLAG(arg_flags, DISSECT_IMAGE_READ_ONLY, false);
+                else if (streq(word, "discard"))
+                        SET_FLAG(arg_flags, DISSECT_IMAGE_DISCARD_ANY, true);
+                else if (streq(word, "nodiscard"))
+                        SET_FLAG(arg_flags, DISSECT_IMAGE_DISCARD_ANY, false);
+                else
+                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                               "Unknown mount option '%s'.", word);
+        }
+
+        if (fake)
+                return 0;
+
+        arg_image = argv[optind];
+        arg_path = argv[optind+1];
+
+        arg_flags |= DISSECT_IMAGE_REQUIRE_ROOT;
+        arg_action = ACTION_MOUNT;
+        return 1;
+}
+
 static int strv_pair_to_json(char **l, JsonVariant **ret) {
        _cleanup_strv_free_ char **jl = NULL;

@@ -1420,7 +1494,10 @@ static int run(int argc, char *argv[]) {

        log_setup();

-        r = parse_argv(argc, argv);
+        if (invoked_as(argv, "mount.ddi"))
+                r = parse_argv_as_mount_helper(argc, argv);
+        else
+                r = parse_argv(argc, argv);
        if (r <= 0)
                return r;

@@ -424,6 +424,12 @@ grep -q -F '{"name":"b","type":"raw","class":"portable","ro":false,"path":"/run/
 grep -q -F '{"name":"c","type":"raw","class":"extension","ro":false,"path":"/run/extensions/c.raw"' /tmp/discover.json
 rm /tmp/discover.json /run/machines/a.raw /run/portables/b.raw /run/extensions/c.raw

+# Check that the /sbin/mount.ddi helper works
+T="/tmp/mounthelper.$RANDOM"
+mount -t ddi "${image}.gpt" "$T" -o ro,X-mount.mkdir,discard
+umount -R "$T"
+rmdir "$T"
+
 echo OK >/testok

 exit 0