diff --git a/Documentation/device-mapper/dm-init.txt b/Documentation/device-mapper/dm-init.txt
new file mode 100644
index 0000000000000000000000000000000000000000..8464ee7c01b82256d01559994d33cb6676c0c5a3
--- /dev/null
+++ b/Documentation/device-mapper/dm-init.txt
@@ -0,0 +1,114 @@
+Early creation of mapped devices
+====================================
+
+It is possible to configure a device-mapper device to act as the root device for
+your system in two ways.
+
+The first is to build an initial ramdisk which boots to a minimal userspace
+which configures the device, then pivot_root(8) in to it.
+
+The second is to create one or more device-mappers using the module parameter
+"dm-mod.create=" through the kernel boot command line argument.
+
+The format is specified as a string of data separated by commas and optionally
+semi-colons, where:
+ - a comma is used to separate fields like name, uuid, flags and table
+ (specifies one device)
+ - a semi-colon is used to separate devices.
+
+So the format will look like this:
+
+ dm-mod.create=<name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]+]
+
+Where,
+ <name> ::= The device name.
+ <uuid> ::= xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx | ""
+ <minor> ::= The device minor number | ""
+ <flags> ::= "ro" | "rw"
+ <table> ::= <start_sector> <num_sectors> <target_type> <target_args>
+ <target_type> ::= "verity" | "linear" | ... (see list below)
+
+The dm line should be equivalent to the one used by the dmsetup tool with the
+--concise argument.
+
+Target types
+============
+
+Not all target types are available as there are serious risks in allowing
+activation of certain DM targets without first using userspace tools to check
+the validity of associated metadata.
+
+ "cache": constrained, userspace should verify cache device
+ "crypt": allowed
+ "delay": allowed
+ "era": constrained, userspace should verify metadata device
+ "flakey": constrained, meant for test
+ "linear": allowed
+ "log-writes": constrained, userspace should verify metadata device
+ "mirror": constrained, userspace should verify main/mirror device
+ "raid": constrained, userspace should verify metadata device
+ "snapshot": constrained, userspace should verify src/dst device
+ "snapshot-origin": allowed
+ "snapshot-merge": constrained, userspace should verify src/dst device
+ "striped": allowed
+ "switch": constrained, userspace should verify dev path
+ "thin": constrained, requires dm target message from userspace
+ "thin-pool": constrained, requires dm target message from userspace
+ "verity": allowed
+ "writecache": constrained, userspace should verify cache device
+ "zero": constrained, not meant for rootfs
+
+If the target is not listed above, it is constrained by default (not tested).
+
+Examples
+========
+An example of booting to a linear array made up of user-mode linux block
+devices:
+
+ dm-mod.create="lroot,,,rw, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" root=/dev/dm-0
+
+This will boot to a rw dm-linear target of 8192 sectors split across two block
+devices identified by their major:minor numbers. After boot, udev will rename
+this target to /dev/mapper/lroot (depending on the rules). No uuid was assigned.
+
+An example of multiple device-mappers, with the dm-mod.create="..." contents is shown here
+split on multiple lines for readability:
+
+ vroot,,,ro,
+ 0 1740800 verity 254:0 254:0 1740800 sha1
+ 76e9be054b15884a9fa85973e9cb274c93afadb6
+ 5b3549d54d6c7a3837b9b81ed72e49463a64c03680c47835bef94d768e5646fe;
+ vram,,,rw,
+ 0 32768 linear 1:0 0,
+ 32768 32768 linear 1:1 0
+
+Other examples (per target):
+
+"crypt":
+ dm-crypt,,8,ro,
+ 0 1048576 crypt aes-xts-plain64
+ babebabebabebabebabebabebabebabebabebabebabebabebabebabebabebabe 0
+ /dev/sda 0 1 allow_discards
+
+"delay":
+ dm-delay,,4,ro,0 409600 delay /dev/sda1 0 500
+
+"linear":
+ dm-linear,,,rw,
+ 0 32768 linear /dev/sda1 0,
+ 32768 1024000 linear /dev/sda2 0,
+ 1056768 204800 linear /dev/sda3 0,
+ 1261568 512000 linear /dev/sda4 0
+
+"snapshot-origin":
+ dm-snap-orig,,4,ro,0 409600 snapshot-origin 8:2
+
+"striped":
+ dm-striped,,4,ro,0 1638400 striped 4 4096
+ /dev/sda1 0 /dev/sda2 0 /dev/sda3 0 /dev/sda4 0
+
+"verity":
+ dm-verity,,4,ro,
+ 0 1638400 verity 1 8:1 8:2 4096 4096 204800 1 sha256
+ fb1a5a0f00deb908d8b53cb270858975e76cf64105d412ce764225d53b8f3cfd
+ 51934789604d1b92399c52e7cb149d1b3a1b74bbbcb103b2a0aaacbed5c08584
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 3db222509e44b456acb46fd2defc1a7978299b8e..2557f198e1750002a1a2d7dacd3fefbb926a7fd7 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -436,6 +436,18 @@ config DM_DELAY
If unsure, say N.
+config DM_INIT
+ bool "DM \"dm-mod.create=\" parameter support"
+ depends on BLK_DEV_DM=y
+ ---help---
+ Enable "dm-mod.create=" parameter to create mapped devices at init time.
+ This option is useful to allow mounting rootfs without requiring an
+ initramfs.
+ See Documentation/device-mapper/dm-init.txt for dm-mod.create="..."
+ format.
+
+ If unsure, say N.
+
config DM_UEVENT
bool "DM uevents"
depends on BLK_DEV_DM
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 822f4e8753bc4b197b93a90df936bd0eeeff464a..a52b703e588e23dfa3a240f8882acc2d1eb29212 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -69,6 +69,10 @@ obj-$(CONFIG_DM_INTEGRITY) += dm-integrity.o
obj-$(CONFIG_DM_ZONED) += dm-zoned.o
obj-$(CONFIG_DM_WRITECACHE) += dm-writecache.o
+ifeq ($(CONFIG_DM_INIT),y)
+dm-mod-objs += dm-init.o
+endif
+
ifeq ($(CONFIG_DM_UEVENT),y)
dm-mod-objs += dm-uevent.o
endif
diff --git a/drivers/md/dm-init.c b/drivers/md/dm-init.c
new file mode 100644
index 0000000000000000000000000000000000000000..b53f30f16b4d4f2c02bf9c15e5b801234b8cd9ae
--- /dev/null
+++ b/drivers/md/dm-init.c
@@ -0,0 +1,303 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * dm-init.c
+ * Copyright (C) 2017 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ *
+ * This file is released under the GPLv2.
+ */
+
+#include <linux/ctype.h>
+#include <linux/device.h>
+#include <linux/device-mapper.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/moduleparam.h>
+
+#define DM_MSG_PREFIX "init"
+#define DM_MAX_DEVICES 256
+#define DM_MAX_TARGETS 256
+#define DM_MAX_STR_SIZE 4096
+
+static char *create;
+
+/*
+ * Format: dm-mod.create=<name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]+]
+ * Table format: <start_sector> <num_sectors> <target_type> <target_args>
+ *
+ * See Documentation/device-mapper/dm-init.txt for dm-mod.create="..." format
+ * details.
+ */
+
+struct dm_device {
+ struct dm_ioctl dmi;
+ struct dm_target_spec *table[DM_MAX_TARGETS];
+ char *target_args_array[DM_MAX_TARGETS];
+ struct list_head list;
+};
+
+const char *dm_allowed_targets[] __initconst = {
+ "crypt",
+ "delay",
+ "linear",
+ "snapshot-origin",
+ "striped",
+ "verity",
+};
+
+static int __init dm_verify_target_type(const char *target)
+{
+ unsigned int i;
+
+ for (i = 0; i < ARRAY_SIZE(dm_allowed_targets); i++) {
+ if (!strcmp(dm_allowed_targets[i], target))
+ return 0;
+ }
+ return -EINVAL;
+}
+
+static void __init dm_setup_cleanup(struct list_head *devices)
+{
+ struct dm_device *dev, *tmp;
+ unsigned int i;
+
+ list_for_each_entry_safe(dev, tmp, devices, list) {
+ list_del(&dev->list);
+ for (i = 0; i < dev->dmi.target_count; i++) {
+ kfree(dev->table[i]);
+ kfree(dev->target_args_array[i]);
+ }
+ kfree(dev);
+ }
+}
+
+/**
+ * str_field_delimit - delimit a string based on a separator char.
+ * @str: the pointer to the string to delimit.
+ * @separator: char that delimits the field
+ *
+ * Find a @separator and replace it by '\0'.
+ * Remove leading and trailing spaces.
+ * Return the remainder string after the @separator.
+ */
+static char __init *str_field_delimit(char **str, char separator)
+{
+ char *s;
+
+ /* TODO: add support for escaped characters */
+ *str = skip_spaces(*str);
+ s = strchr(*str, separator);
+ /* Delimit the field and remove trailing spaces */
+ if (s)
+ *s = '\0';
+ *str = strim(*str);
+ return s ? ++s : NULL;
+}
+
+/**
+ * dm_parse_table_entry - parse a table entry
+ * @dev: device to store the parsed information.
+ * @str: the pointer to a string with the format:
+ * <start_sector> <num_sectors> <target_type> <target_args>[, ...]
+ *
+ * Return the remainder string after the table entry, i.e, after the comma which
+ * delimits the entry or NULL if reached the end of the string.
+ */
+static char __init *dm_parse_table_entry(struct dm_device *dev, char *str)
+{
+ const unsigned int n = dev->dmi.target_count - 1;
+ struct dm_target_spec *sp;
+ unsigned int i;
+ /* fields: */
+ char *field[4];
+ char *next;
+
+ field[0] = str;
+ /* Delimit first 3 fields that are separated by space */
+ for (i = 0; i < ARRAY_SIZE(field) - 1; i++) {
+ field[i + 1] = str_field_delimit(&field[i], ' ');
+ if (!field[i + 1])
+ return ERR_PTR(-EINVAL);
+ }
+ /* Delimit last field that can be terminated by comma */
+ next = str_field_delimit(&field[i], ',');
+
+ sp = kzalloc(sizeof(*sp), GFP_KERNEL);
+ if (!sp)
+ return ERR_PTR(-ENOMEM);
+ dev->table[n] = sp;
+
+ /* start_sector */
+ if (kstrtoull(field[0], 0, &sp->sector_start))
+ return ERR_PTR(-EINVAL);
+ /* num_sector */
+ if (kstrtoull(field[1], 0, &sp->length))
+ return ERR_PTR(-EINVAL);
+ /* target_type */
+ strscpy(sp->target_type, field[2], sizeof(sp->target_type));
+ if (dm_verify_target_type(sp->target_type)) {
+ DMERR("invalid type \"%s\"", sp->target_type);
+ return ERR_PTR(-EINVAL);
+ }
+ /* target_args */
+ dev->target_args_array[n] = kstrndup(field[3], GFP_KERNEL,
+ DM_MAX_STR_SIZE);
+ if (!dev->target_args_array[n])
+ return ERR_PTR(-ENOMEM);
+
+ return next;
+}
+
+/**
+ * dm_parse_table - parse "dm-mod.create=" table field
+ * @dev: device to store the parsed information.
+ * @str: the pointer to a string with the format:
+ * <table>[,<table>+]
+ */
+static int __init dm_parse_table(struct dm_device *dev, char *str)
+{
+ char *table_entry = str;
+
+ while (table_entry) {
+ DMDEBUG("parsing table \"%s\"", str);
+ if (++dev->dmi.target_count >= DM_MAX_TARGETS) {
+ DMERR("too many targets %u > %d",
+ dev->dmi.target_count, DM_MAX_TARGETS);
+ return -EINVAL;
+ }
+ table_entry = dm_parse_table_entry(dev, table_entry);
+ if (IS_ERR(table_entry)) {
+ DMERR("couldn't parse table");
+ return PTR_ERR(table_entry);
+ }
+ }
+
+ return 0;
+}
+
+/**
+ * dm_parse_device_entry - parse a device entry
+ * @dev: device to store the parsed information.
+ * @str: the pointer to a string with the format:
+ * name,uuid,minor,flags,table[; ...]
+ *
+ * Return the remainder string after the table entry, i.e, after the semi-colon
+ * which delimits the entry or NULL if reached the end of the string.
+ */
+static char __init *dm_parse_device_entry(struct dm_device *dev, char *str)
+{
+ /* There are 5 fields: name,uuid,minor,flags,table; */
+ char *field[5];
+ unsigned int i;
+ char *next;
+
+ field[0] = str;
+ /* Delimit first 4 fields that are separated by comma */
+ for (i = 0; i < ARRAY_SIZE(field) - 1; i++) {
+ field[i+1] = str_field_delimit(&field[i], ',');
+ if (!field[i+1])
+ return ERR_PTR(-EINVAL);
+ }
+ /* Delimit last field that can be delimited by semi-colon */
+ next = str_field_delimit(&field[i], ';');
+
+ /* name */
+ strscpy(dev->dmi.name, field[0], sizeof(dev->dmi.name));
+ /* uuid */
+ strscpy(dev->dmi.uuid, field[1], sizeof(dev->dmi.uuid));
+ /* minor */
+ if (strlen(field[2])) {
+ if (kstrtoull(field[2], 0, &dev->dmi.dev))
+ return ERR_PTR(-EINVAL);
+ dev->dmi.flags |= DM_PERSISTENT_DEV_FLAG;
+ }
+ /* flags */
+ if (!strcmp(field[3], "ro"))
+ dev->dmi.flags |= DM_READONLY_FLAG;
+ else if (strcmp(field[3], "rw"))
+ return ERR_PTR(-EINVAL);
+ /* table */
+ if (dm_parse_table(dev, field[4]))
+ return ERR_PTR(-EINVAL);
+
+ return next;
+}
+
+/**
+ * dm_parse_devices - parse "dm-mod.create=" argument
+ * @devices: list of struct dm_device to store the parsed information.
+ * @str: the pointer to a string with the format:
+ * <device>[;<device>+]
+ */
+static int __init dm_parse_devices(struct list_head *devices, char *str)
+{
+ unsigned long ndev = 0;
+ struct dm_device *dev;
+ char *device = str;
+
+ DMDEBUG("parsing \"%s\"", str);
+ while (device) {
+ dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+ if (!dev)
+ return -ENOMEM;
+ list_add_tail(&dev->list, devices);
+
+ if (++ndev >= DM_MAX_DEVICES) {
+ DMERR("too many targets %u > %d",
+ dev->dmi.target_count, DM_MAX_TARGETS);
+ return -EINVAL;
+ }
+
+ device = dm_parse_device_entry(dev, device);
+ if (IS_ERR(device)) {
+ DMERR("couldn't parse device");
+ return PTR_ERR(device);
+ }
+ }
+
+ return 0;
+}
+
+/**
+ * dm_init_init - parse "dm-mod.create=" argument and configure drivers
+ */
+static int __init dm_init_init(void)
+{
+ struct dm_device *dev;
+ LIST_HEAD(devices);
+ char *str;
+ int r;
+
+ if (!create)
+ return 0;
+
+ if (strlen(create) >= DM_MAX_STR_SIZE) {
+ DMERR("Argument is too big. Limit is %d\n", DM_MAX_STR_SIZE);
+ return -EINVAL;
+ }
+ str = kstrndup(create, GFP_KERNEL, DM_MAX_STR_SIZE);
+ if (!str)
+ return -ENOMEM;
+
+ r = dm_parse_devices(&devices, str);
+ if (r)
+ goto out;
+
+ DMINFO("waiting for all devices to be available before creating mapped devices\n");
+ wait_for_device_probe();
+
+ list_for_each_entry(dev, &devices, list) {
+ if (dm_early_create(&dev->dmi, dev->table,
+ dev->target_args_array))
+ break;
+ }
+out:
+ kfree(str);
+ dm_setup_cleanup(&devices);
+ return r;
+}
+
+late_initcall(dm_init_init);
+
+module_param(create, charp, 0);
+MODULE_PARM_DESC(create, "Create a mapped device in early boot");
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index f666778ad23728cdc323f7570d837ebb30ede660..c740153b4e52df15ee7b4cab6c9b1e83d897143f 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -2018,3 +2018,106 @@ int dm_copy_name_and_uuid(struct mapped_device *md, char *name, char *uuid)
return r;
}
+
+
+/**
+ * dm_early_create - create a mapped device in early boot.
+ *
+ * @dmi: Contains main information of the device mapping to be created.
+ * @spec_array: array of pointers to struct dm_target_spec. Describes the
+ * mapping table of the device.
+ * @target_params_array: array of strings with the parameters to a specific
+ * target.
+ *
+ * Instead of having the struct dm_target_spec and the parameters for every
+ * target embedded at the end of struct dm_ioctl (as performed in a normal
+ * ioctl), pass them as arguments, so the caller doesn't need to serialize them.
+ * The size of the spec_array and target_params_array is given by
+ * @dmi->target_count.
+ * This function is supposed to be called in early boot, so locking mechanisms
+ * to protect against concurrent loads are not required.
+ */
+int __init dm_early_create(struct dm_ioctl *dmi,
+ struct dm_target_spec **spec_array,
+ char **target_params_array)
+{
+ int r, m = DM_ANY_MINOR;
+ struct dm_table *t, *old_map;
+ struct mapped_device *md;
+ unsigned int i;
+
+ if (!dmi->target_count)
+ return -EINVAL;
+
+ r = check_name(dmi->name);
+ if (r)
+ return r;
+
+ if (dmi->flags & DM_PERSISTENT_DEV_FLAG)
+ m = MINOR(huge_decode_dev(dmi->dev));
+
+ /* alloc dm device */
+ r = dm_create(m, &md);
+ if (r)
+ return r;
+
+ /* hash insert */
+ r = dm_hash_insert(dmi->name, *dmi->uuid ? dmi->uuid : NULL, md);
+ if (r)
+ goto err_destroy_dm;
+
+ /* alloc table */
+ r = dm_table_create(&t, get_mode(dmi), dmi->target_count, md);
+ if (r)
+ goto err_destroy_dm;
+
+ /* add targets */
+ for (i = 0; i < dmi->target_count; i++) {
+ r = dm_table_add_target(t, spec_array[i]->target_type,
+ (sector_t) spec_array[i]->sector_start,
+ (sector_t) spec_array[i]->length,
+ target_params_array[i]);
+ if (r) {
+ DMWARN("error adding target to table");
+ goto err_destroy_table;
+ }
+ }
+
+ /* finish table */
+ r = dm_table_complete(t);
+ if (r)
+ goto err_destroy_table;
+
+ md->type = dm_table_get_type(t);
+ /* setup md->queue to reflect md's type (may block) */
+ r = dm_setup_md_queue(md, t);
+ if (r) {
+ DMWARN("unable to set up device queue for new table.");
+ goto err_destroy_table;
+ }
+
+ /* Set new map */
+ dm_suspend(md, 0);
+ old_map = dm_swap_table(md, t);
+ if (IS_ERR(old_map)) {
+ r = PTR_ERR(old_map);
+ goto err_destroy_table;
+ }
+ set_disk_ro(dm_disk(md), !!(dmi->flags & DM_READONLY_FLAG));
+
+ /* resume device */
+ r = dm_resume(md);
+ if (r)
+ goto err_destroy_table;
+
+ DMINFO("%s (%s) is ready", md->disk->disk_name, dmi->name);
+ dm_put(md);
+ return 0;
+
+err_destroy_table:
+ dm_table_destroy(t);
+err_destroy_dm:
+ dm_put(md);
+ dm_destroy(md);
+ return r;
+}
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 52e8709c6df08fe3651d5b9eef14e8d30e930e60..b0672756d0562697238cb9cf53775c3c48d87a4a 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -10,6 +10,7 @@
#include <linux/bio.h>
#include <linux/blkdev.h>
+#include <linux/dm-ioctl.h>
#include <linux/math64.h>
#include <linux/ratelimit.h>
@@ -425,6 +426,14 @@ void dm_remap_zone_report(struct dm_target *ti, sector_t start,
struct blk_zone *zones, unsigned int *nr_zones);
union map_info *dm_get_rq_mapinfo(struct request *rq);
+/*
+ * Device mapper functions to parse and create devices specified by the
+ * parameter "dm-mod.create="
+ */
+int __init dm_early_create(struct dm_ioctl *dmi,
+ struct dm_target_spec **spec_array,
+ char **target_params_array);
+
struct queue_limits *dm_get_queue_limits(struct mapped_device *md);
/*