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Subject[PATCH v4 3/3] init: add support to directly boot to a mapped device
Date
This change adds a dm= kernel parameter modeled after the md= parameter
from do_mounts_md. It allows for simple device-mapper targets to be
configured at boot time for use early in the boot process (as the root
device or otherwise).

The format is as follows:
dm="name uuid|none ro|rw, table line 1, table line 2, ..."
It relies on the ability to create a device mapper device programmatically and
bind that device to the ioctl-style name/uuid. In addition, any
/dev/... devices specified in the target parameters will attempt to be
early-resolved with name_to_dev_t.

v4:
- introduces early device resolving with name_to_dev_t,
- moves to 'ro' and 'rw' from 0 and non-zero for read-only

Signed-off-by: Will Drewry <wad@chromium.org>
---
Documentation/device-mapper/boot.txt | 42 ++++
Documentation/kernel-parameters.txt | 4 +
init/Makefile | 1 +
init/do_mounts.c | 1 +
init/do_mounts.h | 10 +
init/do_mounts_dm.c | 414 ++++++++++++++++++++++++++++++++++
6 files changed, 472 insertions(+), 0 deletions(-)
create mode 100644 Documentation/device-mapper/boot.txt
create mode 100644 init/do_mounts_dm.c
diff --git a/Documentation/device-mapper/boot.txt b/Documentation/device-mapper/boot.txt
new file mode 100644
index 0000000..76ea6ac
--- /dev/null
+++ b/Documentation/device-mapper/boot.txt
@@ -0,0 +1,42 @@
+Boot time 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.
+
+For simple device mapper configurations, it is possible to boot directly
+using the following kernel command line:
+
+dm="<name> <uuid> <ro>,table line 1,...,table line n"
+
+name = the name to associate with the device
+ after boot, udev, if used, will use that name to label
+ the device node.
+uuid = may be 'none' or the UUID desired for the device.
+ro = may be 'ro' or 'rw'. If 'ro', the device and device table will be
+ marked read-only.
+
+Each table line may be as normal when using the dmsetup tool except for
+two variations:
+1. Any use of commas will be interpreted as a newline
+2. Quotation marks cannot be escaped and cannot be used without
+ terminating the dm= argument.
+
+Unless renamed by udev, the device node created will be dm-0 as the
+first minor number for the device-mapper is used during early creation.
+
+Example
+=======
+
+- Booting to a linear array made up of user-mode linux block devices:
+
+ dm="lroot none 0, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" \
+ root=/dev/dm-0
+
+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.
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 1808f11..01d85c9 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -43,6 +43,7 @@ parameter is applicable:
AVR32 AVR32 architecture is enabled.
AX25 Appropriate AX.25 support is enabled.
BLACKFIN Blackfin architecture is enabled.
+ DM Device mapper support is enabled.
DRM Direct Rendering Management support is enabled.
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
EFI EFI Partitioning (GPT) is enabled
@@ -655,6 +656,9 @@ and is between 256 and 4096 characters. It is defined in the file
Disable PIN 1 of APIC timer
Can be useful to work around chipset bugs.

+ dm= [DM] Allows early creation of a device-mapper device.
+ See Documentation/device-mapper/boot.txt.
+
dmasound= [HW,OSS] Sound subsystem buffers

dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
diff --git a/init/Makefile b/init/Makefile
index 0bf677a..1677baa 100644
--- a/init/Makefile
+++ b/init/Makefile
@@ -14,6 +14,7 @@ mounts-y := do_mounts.o
mounts-$(CONFIG_BLK_DEV_RAM) += do_mounts_rd.o
mounts-$(CONFIG_BLK_DEV_INITRD) += do_mounts_initrd.o
mounts-$(CONFIG_BLK_DEV_MD) += do_mounts_md.o
+mounts-$(CONFIG_BLK_DEV_DM) += do_mounts_dm.o

# dependencies on generated files need to be listed explicitly
$(obj)/version.o: include/generated/compile.h
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 02e3ca4..0848a5b 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -383,6 +383,7 @@ void __init prepare_namespace(void)
wait_for_device_probe();

md_run_setup();
+ dm_run_setup();

if (saved_root_name[0]) {
root_device_name = saved_root_name;
diff --git a/init/do_mounts.h b/init/do_mounts.h
index f5b978a..09d2286 100644
--- a/init/do_mounts.h
+++ b/init/do_mounts.h
@@ -74,3 +74,13 @@ void md_run_setup(void);
static inline void md_run_setup(void) {}

#endif
+
+#ifdef CONFIG_BLK_DEV_DM
+
+void dm_run_setup(void);
+
+#else
+
+static inline void dm_run_setup(void) {}
+
+#endif
diff --git a/init/do_mounts_dm.c b/init/do_mounts_dm.c
new file mode 100644
index 0000000..b342f8f
--- /dev/null
+++ b/init/do_mounts_dm.c
@@ -0,0 +1,414 @@
+/* do_mounts_dm.c
+ * Copyright (C) 2010 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * All Rights Reserved.
+ * Based on do_mounts_md.c
+ *
+ * This file is released under the GPL.
+ */
+#include <linux/device-mapper.h>
+#include <linux/fs.h>
+#include <linux/string.h>
+
+#include "do_mounts.h"
+
+#define DM_MAX_NAME 32
+#define DM_MAX_UUID 129
+#define DM_NO_UUID "none"
+
+#define DM_MSG_PREFIX "init"
+
+/* Separators used for parsing the dm= argument. */
+#define DM_FIELD_SEP ' '
+#define DM_LINE_SEP ','
+
+/*
+ * When the device-mapper and any targets are compiled into the kernel
+ * (not a module), one target may be created and used as the root device at
+ * boot time with the parameters given with the boot line dm=...
+ * The code for that is here.
+ */
+
+struct dm_setup_target {
+ sector_t begin;
+ sector_t length;
+ char *type;
+ char *params;
+ /* simple singly linked list */
+ struct dm_setup_target *next;
+};
+
+static struct {
+ int minor;
+ int ro;
+ char name[DM_MAX_NAME];
+ char uuid[DM_MAX_UUID];
+ char *targets;
+ struct dm_setup_target *target;
+ int target_count;
+} dm_setup_args __initdata;
+
+static __initdata int dm_early_setup;
+
+static size_t __init get_dm_option(char *str, char **next, char sep)
+{
+ size_t len = 0;
+ char *endp = NULL;
+
+ if (!str)
+ return 0;
+
+ endp = strchr(str, sep);
+ if (!endp) { /* act like strchrnul */
+ len = strlen(str);
+ endp = str + len;
+ } else {
+ len = endp - str;
+ }
+
+ if (endp == str)
+ return 0;
+
+ if (!next)
+ return len;
+
+ if (*endp == 0) {
+ /* Don't advance past the nul. */
+ *next = endp;
+ } else {
+ *next = endp + 1;
+ }
+ return len;
+}
+
+static int __init dm_setup_args_init(void)
+{
+ dm_setup_args.minor = 0;
+ dm_setup_args.ro = 0;
+ dm_setup_args.target = NULL;
+ dm_setup_args.target_count = 0;
+ return 0;
+}
+
+static int __init dm_setup_cleanup(void)
+{
+ struct dm_setup_target *target = dm_setup_args.target;
+ struct dm_setup_target *old_target = NULL;
+ while (target) {
+ kfree(target->type);
+ kfree(target->params);
+ old_target = target;
+ target = target->next;
+ kfree(old_target);
+ dm_setup_args.target_count--;
+ }
+ BUG_ON(dm_setup_args.target_count);
+ return 0;
+}
+
+static char * __init dm_setup_parse_device_args(char *str)
+{
+ char *next = NULL;
+ size_t len = 0;
+
+ /* Grab the logical name of the device to be exported to udev */
+ len = get_dm_option(str, &next, DM_FIELD_SEP);
+ if (!len) {
+ DMERR("failed to parse device name");
+ goto parse_fail;
+ }
+ len = min(len + 1, sizeof(dm_setup_args.name));
+ strlcpy(dm_setup_args.name, str, len); /* includes nul */
+ str = skip_spaces(next);
+
+ /* Grab the UUID value or "none" */
+ len = get_dm_option(str, &next, DM_FIELD_SEP);
+ if (!len) {
+ DMERR("failed to parse device uuid");
+ goto parse_fail;
+ }
+ len = min(len + 1, sizeof(dm_setup_args.uuid));
+ strlcpy(dm_setup_args.uuid, str, len);
+ str = skip_spaces(next);
+
+ /* Determine if the table/device will be read onyl or read-write */
+ if (!strncmp("ro,", str, 3)) {
+ dm_setup_args.ro = 1;
+ } else if (!strncmp("rw,", str, 3)) {
+ dm_setup_args.ro = 0;
+ } else {
+ DMERR("failed to parse table mode");
+ goto parse_fail;
+ }
+ str = skip_spaces(str + 3);
+
+ return str;
+
+parse_fail:
+ return NULL;
+}
+
+static void __init dm_substitute_devices(char *str, size_t str_len)
+{
+ char *candidate = str;
+ char *candidate_end = str;
+ char old_char;
+ size_t len = 0;
+ dev_t dev;
+
+ if (str_len < 3)
+ return;
+
+ while (str && *str) {
+ candidate = strchr(str, '/');
+ if (!candidate)
+ break;
+
+ /* Avoid embedded slashes */
+ if (candidate != str && *(candidate - 1) != DM_FIELD_SEP) {
+ str = strchr(candidate, DM_FIELD_SEP);
+ continue;
+ }
+
+ len = get_dm_option(candidate, &candidate_end, DM_FIELD_SEP);
+ str = skip_spaces(candidate_end);
+ if (len < 3) /* maj:mix min */
+ continue;
+
+ /* Temporarily terminate with a nul */
+ candidate_end--;
+ old_char = *candidate_end;
+ *candidate_end = '\0';
+
+ DMDEBUG("converting candidate device '%s' to dev_t", candidate);
+ /* Use the boot-time specific device naming */
+ dev = name_to_dev_t(candidate);
+ *candidate_end = old_char;
+
+ DMDEBUG(" -> %u", dev);
+ /* No suitable replacement found */
+ if (!dev)
+ continue;
+
+ /* Rewrite the /dev/path as a major:minor */
+ len = snprintf(candidate, len, "%u:%u", MAJOR(dev), MINOR(dev));
+ if (!len) {
+ DMERR("error substituting device major/minor.");
+ break;
+ }
+ candidate += len;
+ /* Pad out with spaces (fixing our nul) */
+ while (candidate < candidate_end)
+ *(candidate++) = DM_FIELD_SEP;
+ }
+}
+
+static int __init dm_setup_parse_targets(char *str)
+{
+ char *next = NULL;
+ size_t len = 0;
+ struct dm_setup_target **target = NULL;
+
+ /* Targets are defined as per the table format but with a
+ * comma as a newline separator.
+ */
+ target = &dm_setup_args.target;
+ while (str && *str) {
+ *target = kzalloc(sizeof(struct dm_setup_target), GFP_KERNEL);
+ if (!*target) {
+ DMERR("failed to allocate memory for target %d",
+ dm_setup_args.target_count);
+ goto parse_fail;
+ }
+ dm_setup_args.target_count++;
+
+ (*target)->begin = simple_strtoull(str, &next, 10);
+ if (!next || *next != DM_FIELD_SEP) {
+ DMERR("failed to parse starting sector for target %d",
+ dm_setup_args.target_count - 1);
+ goto parse_fail;
+ }
+ str = skip_spaces(next + 1);
+
+ (*target)->length = simple_strtoull(str, &next, 10);
+ if (!next || *next != DM_FIELD_SEP) {
+ DMERR("failed to parse length for target %d",
+ dm_setup_args.target_count - 1);
+ goto parse_fail;
+ }
+ str = skip_spaces(next + 1);
+
+ len = get_dm_option(str, &next, DM_FIELD_SEP);
+ if (!len ||
+ !((*target)->type = kstrndup(str, len, GFP_KERNEL))) {
+ DMERR("failed to parse type for target %d",
+ dm_setup_args.target_count - 1);
+ goto parse_fail;
+ }
+ str = skip_spaces(next);
+
+ len = get_dm_option(str, &next, DM_LINE_SEP);
+ if (!len ||
+ !((*target)->params = kstrndup(str, len, GFP_KERNEL))) {
+ DMERR("failed to parse params for target %d",
+ dm_setup_args.target_count - 1);
+ goto parse_fail;
+ }
+ str = skip_spaces(next);
+
+ /* Before moving on, walk through the copied target and
+ * attempt to replace all /dev/xxx with the major:minor number.
+ * It may not be possible to resolve them traditionally at
+ * boot-time.
+ */
+ dm_substitute_devices((*target)->params, len);
+
+ target = &((*target)->next);
+ }
+ DMDEBUG("parsed %d targets", dm_setup_args.target_count);
+
+ return 0;
+
+parse_fail:
+ return 1;
+}
+
+/*
+ * Parse the command-line parameters given our kernel, but do not
+ * actually try to invoke the DM device now; that is handled by
+ * dm_setup_drive after the low-level disk drivers have initialised.
+ * dm format is as follows:
+ * dm="name uuid fmode,[table line 1],[table line 2],..."
+ * May be used with root=/dev/dm-0 as it always uses the first dm minor.
+ */
+
+static int __init dm_setup(char *str)
+{
+ dm_setup_args_init();
+
+ str = dm_setup_parse_device_args(str);
+ if (!str) {
+ DMDEBUG("str is NULL");
+ goto parse_fail;
+ }
+
+ /* Target parsing is delayed until we have dynamic memory */
+ dm_setup_args.targets = str;
+
+ printk(KERN_INFO "dm: will configure '%s' on dm-%d\n",
+ dm_setup_args.name, dm_setup_args.minor);
+
+ dm_early_setup = 1;
+ return 1;
+
+parse_fail:
+ printk(KERN_WARNING "dm: Invalid arguments supplied to dm=.\n");
+ return 0;
+}
+
+
+static void __init dm_setup_drive(void)
+{
+ struct mapped_device *md = NULL;
+ struct dm_table *table = NULL;
+ struct dm_setup_target *target;
+ char *uuid = dm_setup_args.uuid;
+ fmode_t fmode = FMODE_READ;
+
+ /* Finish parsing the targets. */
+ if (dm_setup_parse_targets(dm_setup_args.targets))
+ goto parse_fail;
+
+ if (dm_create(dm_setup_args.minor, &md)) {
+ DMDEBUG("failed to create the device");
+ goto dm_create_fail;
+ }
+ DMDEBUG("created device '%s'", dm_device_name(md));
+
+ /* In addition to flagging the table below, the disk must be
+ * set explicitly ro/rw.
+ */
+ set_disk_ro(dm_disk(md), dm_setup_args.ro);
+
+ if (!dm_setup_args.ro)
+ fmode |= FMODE_WRITE;
+ if (dm_table_create(&table, fmode, dm_setup_args.target_count, md)) {
+ DMDEBUG("failed to create the table");
+ goto dm_table_create_fail;
+ }
+
+ target = dm_setup_args.target;
+ while (target) {
+ DMINFO("adding target '%llu %llu %s %s'",
+ (unsigned long long) target->begin,
+ (unsigned long long) target->length, target->type,
+ target->params);
+ if (dm_table_add_target(table, target->type, target->begin,
+ target->length, target->params)) {
+ DMDEBUG("failed to add the target to the table");
+ goto add_target_fail;
+ }
+ target = target->next;
+ }
+
+ if (dm_table_complete(table)) {
+ DMDEBUG("failed to complete the table");
+ goto table_complete_fail;
+ }
+
+ /* Suspend the device so that we can bind it to the table. */
+ if (dm_suspend(md, 0)) {
+ DMDEBUG("failed to suspend the device pre-bind");
+ goto suspend_fail;
+ }
+
+ /* Bind the table to the device. This is the only way to associate
+ * md->map with the table and set the disk capacity directly.
+ */
+ if (dm_swap_table(md, table)) { /* should return NULL. */
+ DMDEBUG("failed to bind the device to the table");
+ goto table_bind_fail;
+ }
+
+ /* Finally, resume and the device should be ready. */
+ if (dm_resume(md)) {
+ DMDEBUG("failed to resume the device");
+ goto resume_fail;
+ }
+
+ /* Export the dm device via the ioctl interface */
+ if (!strcmp(DM_NO_UUID, dm_setup_args.uuid))
+ uuid = NULL;
+ if (dm_ioctl_export(md, dm_setup_args.name, uuid)) {
+ DMDEBUG("failed to export device with given name and uuid");
+ goto export_fail;
+ }
+ printk(KERN_INFO "dm: dm-%d is ready\n", dm_setup_args.minor);
+
+ dm_setup_cleanup();
+ return;
+
+export_fail:
+resume_fail:
+table_bind_fail:
+suspend_fail:
+table_complete_fail:
+add_target_fail:
+ dm_table_put(table);
+dm_table_create_fail:
+ dm_put(md);
+dm_create_fail:
+ dm_setup_cleanup();
+parse_fail:
+ printk(KERN_WARNING "dm: starting dm-%d (%s) failed\n",
+ dm_setup_args.minor, dm_setup_args.name);
+}
+
+__setup("dm=", dm_setup);
+
+void __init dm_run_setup(void)
+{
+ if (!dm_early_setup)
+ return;
+ printk(KERN_INFO "dm: attempting early device configuration.\n");
+ dm_setup_drive();
+}
--
1.7.0.4


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