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gpt-auto-generator: if root=gpt-auto is specified on kernel cmdline, always wait for /dev/gpt-auto-root symlink

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So far our login in gpt-auto-generator when run in the initrd has been
to generate the units that wait for /dev/gpt-auto-root to show up and
mount them only if we have the loader partition EFI variables set. This
is of course not the case for network boots with a UKI kernel, which
means auto-gpt would not work for mounting the rootfs.

What's nasty is that we don't know for sure whether the "rootdisk"
loopback device will shown up eventually, as it needs explicit
configuration by the user via the kernel cmdline, or could be configured
entirely indepdenently. Hence, let's tweak the logic when we wat for
/dev/gpt-auto-root as device to mount: make the gpt auto root logic a
tristate: if root=gpt-auto is specified on the cmdline *definitely*
enable the logic. If root= is specified and set to anyting else,
*definitely* disable the logic. And if root= is not specified check for
the EFI partition vars – as before – to conditionalized things.

Or in other words, you can now boot the same image either via ESP/local
boot or via netboot with a kernelcmdline image like this:

    rd.systemd.pull=verify=no,machine,blockdev,bootorigin,raw:rootdisk:image.raw root=gpt-auto rootflags=x-systemd.device-timeout=infinity ip=any
This commit is contained in:
Lennart Poettering 2025-02-10 23:15:15 +01:00
parent f8825c1364
commit 1a95fc870a
1 changed files with 28 additions and 19 deletions
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47
src/gpt-auto-generator/gpt-auto-generator.c
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@ -39,7 +39,7 @@
static const char *arg_dest = NULL;
static bool arg_enabled = true;
static bool arg_root_enabled = true;
static int arg_root_enabled = -1; /* tristate */
static bool arg_swap_enabled = true;
static char *arg_root_fstype = NULL;
static char *arg_root_options = NULL;
@ -673,21 +673,29 @@ static int add_root_mount(void) {
_cleanup_free_ char *options = NULL;
int r;
if (!is_efi_boot()) {
log_debug("Not an EFI boot, not creating root mount.");
/* Explicitly disabled? Then exit immediately */
if (arg_root_enabled == 0)
return 0;
/* Neither explicitly enabled nor disabled? Then decide based on the EFI partition variables to be set */
if (arg_root_enabled < 0) {
if (!is_efi_boot()) {
log_debug("Not an EFI boot, not creating root mount.");
return 0;
}
r = efi_loader_get_device_part_uuid(/* ret_uuid= */ NULL);
if (r == -ENOENT) {
log_notice("EFI loader partition unknown, exiting.\n"
"(The boot loader did not set EFI variable LoaderDevicePartUUID.)");
return 0;
}
if (r < 0)
return log_error_errno(r, "Failed to read loader partition UUID: %m");
}
r = efi_loader_get_device_part_uuid(NULL);
if (r == -ENOENT) {
log_notice("EFI loader partition unknown, exiting.\n"
"(The boot loader did not set EFI variable LoaderDevicePartUUID.)");
return 0;
} else if (r < 0)
return log_error_errno(r, "Failed to read loader partition UUID: %m");
/* OK, we have an ESP/XBOOTLDR partition, this is fantastic, so let's wait for a root device to show up.
* A udev rule will create the link for us under the right name. */
/* OK, we shall look for a root device, so let's wait for a root device to show up. A udev rule will
* create the link for us under the right name. */
if (in_initrd()) {
r = generator_write_initrd_root_device_deps(arg_dest, "/dev/gpt-auto-root");
@ -904,9 +912,12 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
/* Disable root disk logic if there's a root= value
* specified (unless it happens to be "gpt-auto") */
if (!streq(value, "gpt-auto")) {
if (streq(value, "gpt-auto")) {
arg_root_enabled = true;
log_debug("Enabling root partition auto-detection, root= is explicitly set to 'gpt_auto'.");
} else {
arg_root_enabled = false;
log_debug("Disabling root partition auto-detection, root= is defined.");
log_debug("Disabling root partition auto-detection, root= is neither unset, nor set to 'gpt-auto'.");
}
} else if (streq(key, "roothash")) {
@ -917,6 +928,7 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
/* Disable root disk logic if there's roothash= defined (i.e. verity enabled) */
arg_root_enabled = false;
log_debug("Disabling root partition auto-detection, roothash= is set.");
} else if (streq(key, "rootfstype")) {
@ -975,10 +987,7 @@ static int run(const char *dest, const char *dest_early, const char *dest_late)
return 0;
}
if (arg_root_enabled)
r = add_root_mount();
else
r = 0;
r = add_root_mount();
if (!in_initrd())
RET_GATHER(r, add_mounts());