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fstab-generator: support defining mount units through kernel command …
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…line

Now, the following kernel command line options are supported:
  systemd.mount-extra=what:where:fstype:options
  systemd.swap-extra=what:options

Closes systemd#27260.
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@yuwata
yuwata committed May 19, 2023
1 parent ea6dc0a commit 1ccafb9
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Showing 2 changed files with 190 additions and 3 deletions.
27 changes: 27 additions & 0 deletions man/systemd-fstab-generator.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -239,6 +239,33 @@
any swap devices configured in <filename>/etc/fstab</filename>.
Defaults to enabled.</para></listitem>
</varlistentry>

<varlistentry>
<term><varname>systemd.mount-extra=<replaceable>WHAT</replaceable>:<replaceable>WHERE</replaceable>[:<replaceable>FSTYPE</replaceable>[:<replaceable>OPTIONS</replaceable>]]</varname></term>

<listitem>
<para>Specifies the mount unit. Takes at least two and at most four fields separated with a colon
(<literal>:</literal>). Each field is handled as the corresponding fstab field. This option can be
specified multiple times.</para>
<para>Example:
<programlisting>
systemd.mount-extra=/dev/sda1:/mount-point:ext4:rw,noatime</programlisting>
</para>
</listitem>
</varlistentry>

<varlistentry>
<term><varname>systemd.swap-extra=<replaceable>WHAT</replaceable>[:<replaceable>OPTIONS</replaceable>]</varname></term>

<listitem>
<para>Specifies the swap unit. Takes the block device to be used as a swap device, and optionally
takes mount options followed by a colon (<literal>:</literal>).</para>
<para>Example:
<programlisting>
systemd.swap=/dev/sda2:x-systemd.makefs</programlisting>
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>

Expand Down
166 changes: 163 additions & 3 deletions src/fstab-generator/fstab-generator.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
#include "mount-setup.h"
#include "mount-util.h"
#include "mountpoint-util.h"
#include "nulstr-util.h"
#include "parse-util.h"
#include "path-util.h"
#include "proc-cmdline.h"
Expand All @@ -45,6 +46,15 @@ typedef enum MountPointFlags {
MOUNT_PCRFS = 1 << 6,
} MountPointFlags;

typedef struct Mount {
char *what;
char *where;
char *fstype;
char *options;
} Mount;

static void mount_array_free(Mount *mounts, size_t n);

static bool arg_sysroot_check = false;
static const char *arg_dest = NULL;
static const char *arg_dest_late = NULL;
Expand All @@ -61,6 +71,8 @@ static char *arg_usr_options = NULL;
static char *arg_usr_hash = NULL;
static VolatileMode arg_volatile_mode = _VOLATILE_MODE_INVALID;
static bool arg_verity = true;
static Mount *arg_mounts = NULL;
static size_t arg_n_mounts = 0;

STATIC_DESTRUCTOR_REGISTER(arg_root_what, freep);
STATIC_DESTRUCTOR_REGISTER(arg_root_fstype, freep);
Expand All @@ -70,6 +82,104 @@ STATIC_DESTRUCTOR_REGISTER(arg_usr_what, freep);
STATIC_DESTRUCTOR_REGISTER(arg_usr_fstype, freep);
STATIC_DESTRUCTOR_REGISTER(arg_usr_options, freep);
STATIC_DESTRUCTOR_REGISTER(arg_usr_hash, freep);
STATIC_ARRAY_DESTRUCTOR_REGISTER(arg_mounts, arg_n_mounts, mount_array_free);

static void mount_done(Mount *m) {
assert(m);

free(m->what);
free(m->where);
free(m->fstype);
free(m->options);
}

static void mount_array_free(Mount *mounts, size_t n) {
FOREACH_ARRAY(m, mounts, n)
mount_done(m);

free(mounts);
}

static int mount_array_add_internal(char *in_what, char *in_where, const char *in_fstype, const char *in_options) {
_cleanup_free_ char *what = NULL, *where = NULL, *fstype = NULL, *options = NULL;
int r;

/* This takes what and where. */

what = ASSERT_PTR(in_what);
where = in_where;

fstype = strdup(isempty(in_fstype) ? "auto" : in_fstype);
if (!fstype)
return -ENOMEM;

if (streq(fstype, "swap")) {
r = free_and_strdup(&where, "none");
if (r < 0)
return r;
}

if (!isempty(in_options)) {
_cleanup_strv_free_ char **options_strv = NULL;

r = strv_split_full(&options_strv, in_options, ",", 0);
if (r < 0)
return r;

r = strv_make_nulstr(options_strv, &options, NULL);
} else
r = strv_make_nulstr(STRV_MAKE("defaults"), &options, NULL);
if (r < 0)
return r;

if (!GREEDY_REALLOC(arg_mounts, arg_n_mounts + 1))
return -ENOMEM;

arg_mounts[arg_n_mounts++] = (Mount) {
.what = TAKE_PTR(what),
.where = TAKE_PTR(where),
.fstype = TAKE_PTR(fstype),
.options = TAKE_PTR(options),
};

return 0;
}

static int mount_array_add(const char *str) {
_cleanup_free_ char *what = NULL, *where = NULL, *fstype = NULL, *options = NULL;
int r;

assert(str);

r = extract_many_words(&str, ":", EXTRACT_CUNESCAPE | EXTRACT_DONT_COALESCE_SEPARATORS,
&what, &where, &fstype, &options, NULL);
if (r < 0)
return r;
if (r < 2)
return -EINVAL;
if (!isempty(str))
return -EINVAL;

return mount_array_add_internal(TAKE_PTR(what), TAKE_PTR(where), fstype, options);
}

static int mount_array_add_swap(const char *str) {
_cleanup_free_ char *what = NULL, *options = NULL;
int r;

assert(str);

r = extract_many_words(&str, ":", EXTRACT_CUNESCAPE | EXTRACT_DONT_COALESCE_SEPARATORS,
&what, &options, NULL);
if (r < 0)
return r;
if (r < 1)
return -EINVAL;
if (!isempty(str))
return -EINVAL;

return mount_array_add_internal(TAKE_PTR(what), NULL, "swap", options);
}

static int write_options(FILE *f, const char *options) {
_cleanup_free_ char *o = NULL;
Expand Down Expand Up @@ -112,17 +222,17 @@ static int add_swap(
assert(what);

if (!arg_swap_enabled) {
log_info("Swap unit generation disabled on kernel command line, ignoring fstab swap entry for %s.", what);
log_info("Swap unit generation disabled on kernel command line, ignoring swap entry for %s.", what);
return 0;
}

if (access("/proc/swaps", F_OK) < 0) {
log_info("Swap not supported, ignoring fstab swap entry for %s.", what);
log_info("Swap not supported, ignoring swap entry for %s.", what);
return 0;
}

if (detect_container() > 0) {
log_info("Running in a container, ignoring fstab swap entry for %s.", what);
log_info("Running in a container, ignoring swap entry for %s.", what);
return 0;
}

Expand Down Expand Up @@ -1151,6 +1261,34 @@ static int add_volatile_var(void) {
SPECIAL_LOCAL_FS_TARGET);
}

static int add_mounts_from_cmdline(void) {
int r, ret = 0;
bool saved;

/* Handle each entries found in cmdline as a fstab entry. */

/* To make swap units specified in systemd.swap-extra= created, even if systemd.swap=no. */
saved = arg_swap_enabled;
arg_swap_enabled = true;

FOREACH_ARRAY(m, arg_mounts, arg_n_mounts) {
r = parse_fstab_one(
"/proc/cmdline",
m->what,
m->where,
m->fstype,
m->options,
/* passno = */ 0,
/* initrd = */ false);
if (r < 0 && ret >= 0)
ret = r;
}

arg_swap_enabled = saved;

return ret;
}

static int parse_proc_cmdline_item(const char *key, const char *value, void *data) {
int r;

Expand Down Expand Up @@ -1255,6 +1393,24 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
log_warning("Failed to parse systemd.verity= kernel command line switch %s. Ignoring.", value);
else
arg_verity = r;

} else if (streq(key, "systemd.mount-extra")) {

if (proc_cmdline_value_missing(key, value))
return 0;

r = mount_array_add(value);
if (r < 0)
log_warning("Failed to parse systemd.mount-extra= option, ignoring: %s", value);

} else if (streq(key, "systemd.swap-extra")) {

if (proc_cmdline_value_missing(key, value))
return 0;

r = mount_array_add_swap(value);
if (r < 0)
log_warning("Failed to parse systemd.swap-extra= option, ignoring: %s", value);
}

return 0;
Expand Down Expand Up @@ -1351,6 +1507,10 @@ static int run_generator(void) {
ret = r;
}

r = add_mounts_from_cmdline();
if (r < 0 && ret >= 0)
ret = r;

return ret;
}

Expand Down

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