On Fri, 29 Jun 2012 12:36:30 -0700 Andrew Boie <andrew.p.boie@xxxxxxxxx>
wrote:
> Android userspace tells the kernel that it wants to boot into recovery
> or some other non-default OS environment by passing a string argument
> to reboot(). It is left to the OEM to hook this up to their specific
> bootloader.
>
> This driver uses the bootloader control block (BCB) in the 'misc'
> partition, which is the AOSP mechanism used to communicate with
> the bootloader. Writing 'bootonce-NNN' to the command field
> will cause the bootloader to do a oneshot boot into an alternate
> boot label NNN if it exists. The device and partition number are
> passed in via kernel command line.
>
> It is the bootloader's job to guard against this area being uninitialzed
> or containing an invalid boot label, and just boot normally if that
> is the case. The bootloader will always populate a magic signature in
> the BCB; the driver will refuse to update it if not present.
>
> Signed-off-by: Andrew Boie <andrew.p.boie@xxxxxxxxx>
Maybe I'm missing something obvious, but why does this need to be implemented
in the kernel? Can't some user-space process just write to that partition
using open/read/seek/write/close before calling 'reboot'.
Thanks,
NeilBrown
> ---
> drivers/staging/android/Kconfig | 11 ++
> drivers/staging/android/Makefile | 1 +
> drivers/staging/android/bcb.c | 232 ++++++++++++++++++++++++++++++++++++++
> 3 files changed, 244 insertions(+)
> create mode 100644 drivers/staging/android/bcb.c
>
> diff --git a/drivers/staging/android/Kconfig b/drivers/staging/android/Kconfig
> index 9a99238..c30fd20 100644
> --- a/drivers/staging/android/Kconfig
> +++ b/drivers/staging/android/Kconfig
> @@ -78,6 +78,17 @@ config ANDROID_INTF_ALARM_DEV
> elapsed realtime, and a non-wakeup alarm on the monotonic clock.
> Also exports the alarm interface to user-space.
>
> +config BOOTLOADER_CONTROL
> + tristate "Bootloader Control Block module"
> + default n
> + help
> + This driver installs a reboot hook, such that if reboot() is invoked
> + with a string argument NNN, "bootonce-NNN" is copied to the command
> + field in the Bootloader Control Block on the /misc partition, to be
> + read by the bootloader. If the string matches one of the boot labels
> + defined in its configuration, it will boot once into that label. The
> + device and partition number are specified on the kernel command line.
> +
> endif # if ANDROID
>
> endmenu
> diff --git a/drivers/staging/android/Makefile b/drivers/staging/android/Makefile
> index 8e18d4e..a27707f 100644
> --- a/drivers/staging/android/Makefile
> +++ b/drivers/staging/android/Makefile
> @@ -9,5 +9,6 @@ obj-$(CONFIG_ANDROID_LOW_MEMORY_KILLER) += lowmemorykiller.o
> obj-$(CONFIG_ANDROID_SWITCH) += switch/
> obj-$(CONFIG_ANDROID_INTF_ALARM_DEV) += alarm-dev.o
> obj-$(CONFIG_PERSISTENT_TRACER) += trace_persistent.o
> +obj-$(CONFIG_BOOTLOADER_CONTROL) += bcb.o
>
> CFLAGS_REMOVE_trace_persistent.o = -pg
> diff --git a/drivers/staging/android/bcb.c b/drivers/staging/android/bcb.c
> new file mode 100644
> index 0000000..af75257
> --- /dev/null
> +++ b/drivers/staging/android/bcb.c
> @@ -0,0 +1,232 @@
> +/*
> + * bcb.c: Reboot hook to write bootloader commands to
> + * the Android bootloader control block
> + *
> + * (C) Copyright 2012 Intel Corporation
> + * Author: Andrew Boie <andrew.p.boie@xxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; version 2
> + * of the License.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/moduleparam.h>
> +#include <linux/blkdev.h>
> +#include <linux/reboot.h>
> +
> +#define BCB_MAGIC 0xFEEDFACE
> +
> +/* Persistent area written by Android recovery console and Linux bcb driver
> + * reboot hook for communication with the bootloader. Bootloader must
> + * gracefully handle this area being unitinitailzed */
> +struct bootloader_message {
> + /* Directive to the bootloader on what it needs to do next.
> + * Possible values:
> + * boot-NNN - Automatically boot into label NNN
> + * bootonce-NNN - Automatically boot into label NNN, clearing this
> + * field afterwards
> + * anything else / garbage - Boot default label */
> + char command[32];
> +
> + /* Storage area for error codes when using the BCB to boot into special
> + * boot targets, e.g. for baseband update. Not used here. */
> + char status[32];
> +
> + /* Area for recovery console to stash its command line arguments
> + * in case it is reset and the cache command file is erased.
> + * Not used here. */
> + char recovery[1024];
> +
> + /* Magic sentinel value written by the bootloader; don't update this
> + * if not equalto to BCB_MAGIC */
> + uint32_t magic;
> +};
> +
> +/* TODO: device names/partition numbers are unstable. Add support for looking
> + * by GPT partition UUIDs */
> +static char *bootdev = "sda";
> +module_param(bootdev, charp, S_IRUGO);
> +MODULE_PARM_DESC(bootdev, "Block device for bootloader communication");
> +
> +static int partno;
> +module_param(partno, int, S_IRUGO);
> +MODULE_PARM_DESC(partno, "Partition number for bootloader communication");
> +
> +static int device_match(struct device *dev, void *data)
> +{
> + if (strcmp(dev_name(dev), bootdev) == 0)
> + return 1;
> + return 0;
> +}
> +
> +static struct block_device *get_emmc_bdev(void)
> +{
> + struct block_device *bdev;
> + struct device *disk_device;
> +
> + disk_device = class_find_device(&block_class, NULL, NULL, device_match);
> + if (!disk_device) {
> + pr_err("bcb: device %s not found!\n", bootdev);
> + return NULL;
> + }
> + bdev = bdget_disk(dev_to_disk(disk_device), partno);
> + if (!bdev) {
> + dev_err(disk_device, "bcb: unable to get disk (%s,%d)\n",
> + bootdev, partno);
> + return NULL;
> + }
> + /* Note: this bdev ref will be freed after first
> + bdev_get/bdev_put cycle */
> + return bdev;
> +}
> +
> +static u64 last_lba(struct block_device *bdev)
> +{
> + if (!bdev || !bdev->bd_inode)
> + return 0;
> + return div_u64(bdev->bd_inode->i_size,
> + bdev_logical_block_size(bdev)) - 1ULL;
> +}
> +
> +static size_t read_lba(struct block_device *bdev,
> + u64 lba, u8 *buffer, size_t count)
> +{
> + size_t totalreadcount = 0;
> + sector_t n = lba * (bdev_logical_block_size(bdev) / 512);
> +
> + if (!buffer || lba > last_lba(bdev))
> + return 0;
> +
> + while (count) {
> + int copied = 512;
> + Sector sect;
> + unsigned char *data = read_dev_sector(bdev, n++, §);
> + if (!data)
> + break;
> + if (copied > count)
> + copied = count;
> + memcpy(buffer, data, copied);
> + put_dev_sector(sect);
> + buffer += copied;
> + totalreadcount += copied;
> + count -= copied;
> + }
> + return totalreadcount;
> +}
> +
> +static size_t write_lba(struct block_device *bdev,
> + u64 lba, u8 *buffer, size_t count)
> +{
> + size_t totalwritecount = 0;
> + sector_t n = lba * (bdev_logical_block_size(bdev) / 512);
> +
> + if (!buffer || lba > last_lba(bdev))
> + return 0;
> +
> + while (count) {
> + int copied = 512;
> + Sector sect;
> + unsigned char *data = read_dev_sector(bdev, n++, §);
> + if (!data)
> + break;
> + if (copied > count)
> + copied = count;
> + memcpy(data, buffer, copied);
> + set_page_dirty(sect.v);
> + unlock_page(sect.v);
> + put_dev_sector(sect);
> + buffer += copied;
> + totalwritecount += copied;
> + count -= copied;
> + }
> + sync_blockdev(bdev);
> + return totalwritecount;
> +}
> +
> +static int bcb_reboot_notifier_call(
> + struct notifier_block *notifier,
> + unsigned long what, void *data)
> +{
> + int ret = NOTIFY_DONE;
> + char *cmd = (char *)data;
> + struct block_device *bdev = NULL;
> + struct bootloader_message *bcb = NULL;
> +
> + if (what != SYS_RESTART || !data)
> + goto out;
> +
> + bdev = get_emmc_bdev();
> + if (!bdev)
> + goto out;
> +
> + /* make sure the block device is open rw */
> + if (blkdev_get(bdev, FMODE_READ | FMODE_WRITE, NULL) < 0) {
> + pr_err("bcb: blk_dev_get failed!\n");
> + goto out;
> + }
> +
> + bcb = kmalloc(sizeof(*bcb), GFP_KERNEL);
> + if (!bcb) {
> + pr_err("bcb: out of memory\n");
> + goto out;
> + }
> +
> + if (read_lba(bdev, 0, (u8 *)bcb, sizeof(*bcb)) != sizeof(*bcb)) {
> + pr_err("bcb: couldn't read bootloader control block\n");
> + goto out;
> + }
> +
> + if (bcb->magic != BCB_MAGIC) {
> + pr_err("bcb: bootloader control block corrupted, not writing\n");
> + goto out;
> + }
> +
> + /* When the bootloader reads this area, it will null-terminate it
> + * and check if it matches any existing boot labels */
> + snprintf(bcb->command, sizeof(bcb->command), "bootonce-%s", cmd);
> +
> + if (write_lba(bdev, 0, (u8 *)bcb, sizeof(*bcb)) != sizeof(*bcb)) {
> + pr_err("bcb: couldn't write bootloader control block\n");
> + goto out;
> + }
> +
> + ret = NOTIFY_OK;
> +out:
> + kfree(bcb);
> + if (bdev)
> + blkdev_put(bdev, FMODE_READ | FMODE_WRITE);
> +
> + return ret;
> +}
> +
> +static struct notifier_block bcb_reboot_notifier = {
> + .notifier_call = bcb_reboot_notifier_call,
> +};
> +
> +static int __init bcb_init(void)
> +{
> + if (partno < 1) {
> + pr_err("bcb: partition number not specified\n");
> + return -1;
> + }
> + if (register_reboot_notifier(&bcb_reboot_notifier)) {
> + pr_err("bcb: unable to register reboot notifier\n");
> + return -1;
> + }
> + pr_info("bcb: writing commands to (%s,%d)\n",
> + bootdev, partno);
> + return 0;
> +}
> +module_init(bcb_init);
> +
> +static void __exit bcb_exit(void)
> +{
> + unregister_reboot_notifier(&bcb_reboot_notifier);
> +}
> +module_exit(bcb_exit);
> +
> +MODULE_AUTHOR("Andrew Boie <andrew.p.boie@xxxxxxxxx>");
> +MODULE_DESCRIPTION("bootloader communication module");
> +MODULE_LICENSE("GPL v2");
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