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fstab-generator: support creating bind mounts via root= kernel cmdline switches

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This is useful for bind mounting a freshly downloaded and unpacked tar
disk images to /sysroot to mount into.

Specifically, with a kernel command line like this one:

  rd.systemd.pull=verify=no,machine,tar:root:http://_gateway:8081/image.tar root=bind:/run/machines/root ip=any

The first parameter downloads the root image, the second one then binds
it to /sysroot so that we can boot into it.
This commit is contained in:
Lennart Poettering
2025-02-10 12:56:08 +01:00
parent 8b918a3a38
commit b4bee5684d
8 changed files with 112 additions and 51 deletions
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4
man/systemd-fstab-generator.xml
View File

@@ -99,6 +99,10 @@
separate, immutable <filename>/usr/</filename> file system. Also see
<varname>systemd.volatile=</varname> below.</para>
<para>Use <literal>bind:…</literal> to bind mount another directory as operating system root
filesystems (added in v258). Expects an absolute path name referencing an existing directory within the initrd's file
hierarchy to boot into.</para>
<xi:include href="version-info.xml" xpointer="v217"/></listitem>
</varlistentry>

10
man/systemd-import-generator.xml
View File

@@ -242,6 +242,16 @@
<literal>http://example.com/image.efi</literal> this would result in a root disk being downloaded from
<literal>http://example.com/image.raw.xz</literal>.</para>
</example>
<example>
<title>Boot into disk image (tar), with URL derived from UEFI HTTP network booting</title>
<programlisting>systemd.pull=tar,machine,verify=no,bootorigin:root:image.tar.xz root=bind:/run/machines/root</programlisting>
<para>This is similar to the previous example, but instead of a raw (i.e. block device based) disk
image the system boots into a tarball that is downloaded from the originating UEFI network
server.</para>
</example>
</refsect1>
<refsect1>

144
src/fstab-generator/fstab-generator.c
View File

@@ -494,7 +494,8 @@ static int add_mount(
const char *opts,
int passno,
MountPointFlags flags,
const char *target_unit) {
const char *target_unit,
const char *extra_after) {
_cleanup_free_ char *name = NULL, *automount_name = NULL, *filtered = NULL, *where_escaped = NULL,
*opts_root_filtered = NULL;
@@ -596,6 +597,9 @@ static int add_mount(
if (target_unit && !FLAGS_SET(flags, MOUNT_NOFAIL))
fprintf(f, "Before=%s\n", target_unit);
if (extra_after)
fprintf(f, "After=%s\n", extra_after);
if (passno != 0) {
r = generator_write_fsck_deps(f, dest, what, where, fstype);
if (r < 0)
@@ -814,15 +818,16 @@ static bool sysfs_check(void) {
static int add_sysusr_sysroot_usr_bind_mount(const char *source) {
return add_mount(source,
arg_dest,
"/sysusr/usr",
"/sysroot/usr",
NULL,
NULL,
"bind",
0,
0,
SPECIAL_INITRD_FS_TARGET);
arg_dest,
"/sysusr/usr",
"/sysroot/usr",
/* original_where= */ NULL,
/* fstype= */ NULL,
"bind",
/* passno= */ 0,
/* flags= */ 0,
SPECIAL_INITRD_FS_TARGET,
/* extra_after= */ NULL);
}
static MountPointFlags fstab_options_to_flags(const char *options, bool is_swap) {
@@ -1000,7 +1005,8 @@ static int parse_fstab_one(
options,
passno,
flags,
target_unit);
target_unit,
/* extra_after= */ NULL);
if (r <= 0)
return r;
@@ -1105,8 +1111,8 @@ static int sysroot_is_nfsroot(void) {
static int add_sysroot_mount(void) {
_cleanup_free_ char *what = NULL;
const char *opts, *fstype;
bool default_rw, makefs;
const char *extra_opts = NULL, *fstype = NULL;
bool default_rw = true, makefs = false;
MountPointFlags flags;
int r;
@@ -1149,7 +1155,20 @@ static int add_sysroot_mount(void) {
return 0;
}
if (streq(arg_root_what, "tmpfs")) {
const char *bind = startswith(arg_root_what, "bind:");
if (bind) {
if (!path_is_valid(bind) || !path_is_absolute(bind)) {
log_debug("Invalid root=bind: source path, ignoring: %s", bind);
return 0;
}
what = strdup(bind);
if (!what)
return log_oom();
extra_opts = "bind";
} else if (streq(arg_root_what, "tmpfs")) {
/* If root=tmpfs is specified, then take this as shortcut for a writable tmpfs mount as root */
what = strdup("rootfs"); /* just a pretty name, to show up in /proc/self/mountinfo */
@@ -1157,8 +1176,6 @@ static int add_sysroot_mount(void) {
return log_oom();
fstype = arg_root_fstype ?: "tmpfs"; /* tmpfs, unless overridden */
default_rw = true; /* writable, unless overridden */;
} else {
what = fstab_node_to_udev_node(arg_root_what);
@@ -1166,40 +1183,44 @@ static int add_sysroot_mount(void) {
return log_oom();
fstype = arg_root_fstype; /* if not specified explicitly, don't default to anything here */
default_rw = false; /* read-only, unless overridden */
}
if (!arg_root_options)
opts = arg_root_rw > 0 || (arg_root_rw < 0 && default_rw) ? "rw" : "ro";
else if (arg_root_rw >= 0 ||
!fstab_test_option(arg_root_options, "ro\0" "rw\0"))
opts = strjoina(arg_root_options, ",", arg_root_rw > 0 ? "rw" : "ro");
else
opts = arg_root_options;
_cleanup_free_ char *combined_options = NULL;
if (strdup_to(&combined_options, arg_root_options) < 0)
return log_oom();
log_debug("Found entry what=%s where=/sysroot type=%s opts=%s", what, strna(arg_root_fstype), strempty(opts));
if (arg_root_rw >= 0 || !fstab_test_option(combined_options, "ro\0" "rw\0"))
if (!strextend_with_separator(&combined_options, ",", arg_root_rw > 0 || (arg_root_rw < 0 && default_rw) ? "rw" : "ro"))
return log_oom();
makefs = fstab_test_option(opts, "x-systemd.makefs\0");
if (extra_opts)
if (!strextend_with_separator(&combined_options, ",", extra_opts))
return log_oom();
log_debug("Found entry what=%s where=/sysroot type=%s opts=%s", what, strna(arg_root_fstype), strempty(combined_options));
makefs = fstab_test_option(combined_options, "x-systemd.makefs\0");
flags = makefs * MOUNT_MAKEFS;
return add_mount("/proc/cmdline",
arg_dest,
what,
"/sysroot",
NULL,
/* original_where= */ NULL,
fstype,
opts,
is_device_path(what) ? 1 : 0, /* passno */
flags, /* makefs off, pcrfs off, quota off, noauto off, nofail off, automount off */
SPECIAL_INITRD_ROOT_FS_TARGET);
combined_options,
/* passno= */ is_device_path(what) ? 1 : 0,
flags,
SPECIAL_INITRD_ROOT_FS_TARGET,
"imports.target");
}
static int add_sysroot_usr_mount(void) {
_cleanup_free_ char *what = NULL;
const char *opts;
bool makefs;
const char *extra_opts = NULL;
MountPointFlags flags;
bool makefs;
int r;
/* Returns 0 if we didn't do anything, > 0 if we either generated a unit for the /usr/ mount, or we
@@ -1250,16 +1271,35 @@ static int add_sysroot_usr_mount(void) {
return 1; /* As above, report that NFS code will create the unit */
}
what = fstab_node_to_udev_node(arg_usr_what);
if (!what)
const char *bind = startswith(arg_usr_what, "bind:");
if (bind) {
if (!path_is_valid(bind) || !path_is_absolute(bind)) {
log_debug("Invalid mount.usr=bind: source path, ignoring: %s", bind);
return 0;
}
what = strdup(bind);
if (!what)
return log_oom();
extra_opts = "bind";
} else {
what = fstab_node_to_udev_node(arg_usr_what);
if (!what)
return log_oom();
}
_cleanup_free_ char *combined_options = NULL;
if (strdup_to(&combined_options, arg_usr_options) < 0)
return log_oom();
if (!arg_usr_options)
opts = arg_root_rw > 0 ? "rw" : "ro";
else if (!fstab_test_option(arg_usr_options, "ro\0" "rw\0"))
opts = strjoina(arg_usr_options, ",", arg_root_rw > 0 ? "rw" : "ro");
else
opts = arg_usr_options;
if (!fstab_test_option(combined_options, "ro\0" "rw\0"))
if (!strextend_with_separator(&combined_options, ",", arg_root_rw > 0 ? "rw" : "ro"))
return log_oom();
if (extra_opts)
if (!strextend_with_separator(&combined_options, ",", extra_opts))
return log_oom();
/* When mounting /usr from the initrd, we add an extra level of indirection: we first mount the /usr/
* partition to /sysusr/usr/, and then afterwards bind mount that to /sysroot/usr/. We do this so
@@ -1268,21 +1308,22 @@ static int add_sysroot_usr_mount(void) {
* this should order itself after initrd-usr-fs.target and before initrd-fs.target; and it should
* look into both /sysusr/ and /sysroot/ for the configuration data to apply. */
log_debug("Found entry what=%s where=/sysusr/usr type=%s opts=%s", what, strna(arg_usr_fstype), strempty(opts));
log_debug("Found entry what=%s where=/sysusr/usr type=%s opts=%s", what, strna(arg_usr_fstype), strempty(combined_options));
makefs = fstab_test_option(opts, "x-systemd.makefs\0");
makefs = fstab_test_option(combined_options, "x-systemd.makefs\0");
flags = makefs * MOUNT_MAKEFS;
r = add_mount("/proc/cmdline",
arg_dest,
what,
"/sysusr/usr",
NULL,
/* original_where= */ NULL,
arg_usr_fstype,
opts,
is_device_path(what) ? 1 : 0, /* passno */
combined_options,
/* passno= */ is_device_path(what) ? 1 : 0,
flags,
SPECIAL_INITRD_USR_FS_TARGET);
SPECIAL_INITRD_USR_FS_TARGET,
"imports.target");
if (r < 0)
return r;
@@ -1336,12 +1377,13 @@ static int add_volatile_var(void) {
arg_dest_late,
"tmpfs",
"/var",
NULL,
/* original_where= */ NULL,
"tmpfs",
"mode=0755" TMPFS_LIMITS_VAR,
0,
0,
SPECIAL_LOCAL_FS_TARGET);
/* passno= */ 0,
/* flags= */ 0,
SPECIAL_LOCAL_FS_TARGET,
/* extra_after= */ NULL);
}
static int add_mounts_from_cmdline(void) {

1
test/test-fstab-generator/test-12-dev-sdx.expected/sysroot.mount
View File

@@ -4,6 +4,7 @@
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
SourcePath=/proc/cmdline
Before=initrd-root-fs.target
After=imports.target
Requires=systemd-fsck-root.service
After=systemd-fsck-root.service
After=blockdev@dev-sdx1.target

1
test/test-fstab-generator/test-13-label.expected/sysroot.mount
View File

@@ -4,6 +4,7 @@
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
SourcePath=/proc/cmdline
Before=initrd-root-fs.target
After=imports.target
Requires=systemd-fsck-root.service
After=systemd-fsck-root.service
After=blockdev@dev-disk-by\x2dlabel-Root.target

1
test/test-fstab-generator/test-14-uuid.expected/sysroot.mount
View File

@@ -4,6 +4,7 @@
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
SourcePath=/proc/cmdline
Before=initrd-root-fs.target
After=imports.target
Requires=systemd-fsck-root.service
After=systemd-fsck-root.service
After=blockdev@dev-disk-by\x2duuid-3f5ad593\x2d4546\x2d4a94\x2da374\x2dbcfb68aa11f7.target

1
test/test-fstab-generator/test-15-partuuid.expected/sysroot.mount
View File

@@ -4,6 +4,7 @@
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
SourcePath=/proc/cmdline
Before=initrd-root-fs.target
After=imports.target
Requires=systemd-fsck-root.service
After=systemd-fsck-root.service
After=blockdev@dev-disk-by\x2dpartuuid-3f5ad593\x2d4546\x2d4a94\x2da374\x2dbcfb68aa11f7.target

1
test/test-fstab-generator/test-16-tmpfs.expected/sysroot.mount
View File

@@ -4,6 +4,7 @@
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
SourcePath=/proc/cmdline
Before=initrd-root-fs.target
After=imports.target
[Mount]
What=rootfs