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Add support for boot environment data to be stored in the label

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Modern bootloaders leverage data stored in the root filesystem to 
enable some of their powerful features. GRUB specifically has a grubenv 
file which can store large amounts of configuration data that can be 
read and written at boot time and during normal operation. This allows 
sysadmins to configure useful features like automated failover after 
failed boot attempts. Unfortunately, due to the Copy-on-Write nature 
of ZFS, the standard behavior of these tools cannot handle writing to
ZFS files safely at boot time. We need an alternative way to store 
data that allows the bootloader to make changes to the data.

This work is very similar to work that was done on Illumos to enable 
similar functionality in the FreeBSD bootloader. This patch is different 
in that the data being stored is a raw grubenv file; this file can store 
arbitrary variables and values, and the scripting provided by grub is 
powerful enough that special structures are not required to implement 
advanced behavior.

We repurpose the second padding area in each label to store the grubenv 
file, protected by an embedded checksum. We add two ioctls to get and 
set this data, and libzfs_core and libzfs functions to access them more 
easily. There are no direct command line interfaces to these functions; 
these will be added directly to the bootloader utilities.

Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #10009
This commit is contained in:
Paul Dagnelie
2020-05-07 09:36:33 -07:00
committed by GitHub
parent a36bad1759
commit 108a454a46
13 changed files with 335 additions and 22 deletions
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module/zfs/zfs_ioctl.c
+62
View File
@@ -3512,6 +3512,58 @@ zfs_ioc_log_history(const char *unused, nvlist_t *innvl, nvlist_t *outnvl)
return (error);
}
/*
* This ioctl is used to set the bootenv configuration on the current
* pool. This configuration is stored in the second padding area of the label,
* and it is used by the GRUB bootloader used on Linux to store the contents
* of the grubenv file. The file is stored as raw ASCII, and is protected by
* an embedded checksum. By default, GRUB will check if the boot filesystem
* supports storing the environment data in a special location, and if so,
* will invoke filesystem specific logic to retrieve it. This can be overriden
* by a variable, should the user so desire.
*/
/* ARGSUSED */
static const zfs_ioc_key_t zfs_keys_set_bootenv[] = {
{"envmap", DATA_TYPE_STRING, 0},
};
static int
zfs_ioc_set_bootenv(const char *name, nvlist_t *innvl, nvlist_t *outnvl)
{
char *envmap;
int error;
spa_t *spa;
envmap = fnvlist_lookup_string(innvl, "envmap");
if ((error = spa_open(name, &spa, FTAG)) != 0)
return (error);
spa_vdev_state_enter(spa, SCL_ALL);
error = vdev_label_write_bootenv(spa->spa_root_vdev, envmap);
(void) spa_vdev_state_exit(spa, NULL, 0);
spa_close(spa, FTAG);
return (error);
}
static const zfs_ioc_key_t zfs_keys_get_bootenv[] = {
/* no nvl keys */
};
/* ARGSUSED */
static int
zfs_ioc_get_bootenv(const char *name, nvlist_t *innvl, nvlist_t *outnvl)
{
spa_t *spa;
int error;
if ((error = spa_open(name, &spa, FTAG)) != 0)
return (error);
spa_vdev_state_enter(spa, SCL_ALL);
error = vdev_label_read_bootenv(spa->spa_root_vdev, outnvl);
(void) spa_vdev_state_exit(spa, NULL, 0);
spa_close(spa, FTAG);
return (error);
}
/*
* The dp_config_rwlock must not be held when calling this, because the
* unmount may need to write out data.
@@ -6981,6 +7033,16 @@ zfs_ioctl_init(void)
POOL_CHECK_SUSPENDED | POOL_CHECK_READONLY, B_FALSE, B_FALSE,
zfs_keys_fs_wait, ARRAY_SIZE(zfs_keys_fs_wait));
zfs_ioctl_register("set_bootenv", ZFS_IOC_SET_BOOTENV,
zfs_ioc_set_bootenv, zfs_secpolicy_config, POOL_NAME,
POOL_CHECK_SUSPENDED | POOL_CHECK_READONLY, B_FALSE, B_TRUE,
zfs_keys_set_bootenv, ARRAY_SIZE(zfs_keys_set_bootenv));
zfs_ioctl_register("get_bootenv", ZFS_IOC_GET_BOOTENV,
zfs_ioc_get_bootenv, zfs_secpolicy_none, POOL_NAME,
POOL_CHECK_SUSPENDED, B_FALSE, B_TRUE,
zfs_keys_get_bootenv, ARRAY_SIZE(zfs_keys_get_bootenv));
/* IOCTLS that use the legacy function signature */
zfs_ioctl_register_legacy(ZFS_IOC_POOL_FREEZE, zfs_ioc_pool_freeze,