Add a "create" module parameter, which allows device-mapper targets to be
configured at boot time. This enables early use of dm targets in the boot
process (as the root device or otherwise) without the need of an initramfs.
The syntax used in the boot param is based on the concise format from the
dmsetup tool to follow the rule of least surprise:
sudo dmsetup table --concise /dev/mapper/lroot
Which is:
dm-mod.create=[,+][;[,+]+]
Where,
::= The device name.
::= ---- | ""
::= The device minor number | ""
::= "ro" | "rw"
::=
::= "verity" | "linear" | ...
For example, the following could be added in the boot parameters:
dm-mod.create="lroot,,,rw, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0"
root=/dev/dm-0
Only the targets that were tested are allowed and the ones that doesn't
change any block device when the dm is create as read-only. For example,
mirror and cache targets are not allowed. The rationale behind this is
that if the user makes a mistake, choosing the wrong device to be the
mirror or the cache can corrupt data.
The only targets allowed are:
* crypt
* delay
* linear
* snapshot-origin
* striped
* verity
Co-developed-by: Will Drewry
Co-developed-by: Kees Cook
Co-developed-by: Enric Balletbo i Serra
Signed-off-by: Helen Koike
---
Hello,
Just re-sending updating the patch header.
Thanks
Helen
Changes in v12:
- commit message updated
- v11:
https://www.redhat.com/archives/dm-devel/2019-February/msg00108.html
Changes in v11:
- Configure the device directly instead of performing in IOCTL (this
removed a lot of parsing code)
- Just enable the targets that were tested.
- Simplify/refactor parsing, as a consequence, escaping characters is not
allowed (but it wans't properly used in the previous version anyway)
- don't use sscanf, the size wans't being limited and we could have a
buffer overflow.
- change constrained targets list
- remove code from init/
- use a module parameter instead of a kernel comand line parameter in
init/
- rename dm-boot to dm-init
Changes in v10:
- https://lore.kernel.org/patchwork/project/lkml/list/?series=371523
- new file: drivers/md/dm-boot.c
- most of the parsing code was moved from init/do_mounts_dm.c to
drivers/md/dm-boot.c
- parsing code was in essence replaced by the concise parser from dmsetup
_create_concise function:
https://sourceware.org/git/?p=lvm2.git;a=blob;f=libdm/dm-tools/dmsetup.c;h=835fdcdc75e8f0f0f7c4ed46cc9788a6616f58b8;hb=7498f8383397a93db95655ca227257836cbcac82#l1265
the main reason is that this code is already being used/tested by dmsetup, so
we can have some level of confidence that it works as expected. Besides this,
it also looks more efficient.
- Not all targets are allowed to be used by dm=, as pointed previously, there
are some risks in creating a mapped device without some validation from
userspace (see documentation from the patch listing which targets are allowed).
- Instead of using a simple singly linked list (for devices and tables), use
the struct list_head. This occupies unnecessary space in the code, but it makes
the code cleaner and easier to read and less prone to silly errors.
- Documentation and comments were reviewed and refactored, e.g.:
* "is to possible" was removed
* s/specified as a simple string/specified as a string/
- Added docs above __align function, make it clear that the second parameter @a
must be a power of two.
- Clean ups: removal of unnecessary includes, macros, variables, some redundant
checks and warnings.
- when calling ioctls, the code was allocating and freeing the same structure
a couple of times. So instead of executing kzalloc/kfree 3 times, execute
kmalloc once and reuse the structure after a memset, then finally kfree it
once.
- update commit message
Changes in v9:
- https://www.redhat.com/archives/linux-lvm/2018-September/msg00016.html
- Add minor number to make it compatible with dmsetup concise format
Changes in v8:
- https://www.redhat.com/archives/linux-lvm/2017-May/msg00055.html
- Fix build error due commit
e516db4f67 (dm ioctl: add a new DM_DEV_ARM_POLL ioctl)
Changes in v7:
- http://lkml.iu.edu/hypermail/linux/kernel/1705.2/02657.html
- Add a new function to issue the equivalent of a DM ioctl programatically.
- Use the new ioctl interface to create the devices.
- Use a comma-delimited and semi-colon delimited dmsetup-like commands.
Changes in v6:
- https://www.redhat.com/archives/dm-devel/2017-April/msg00316.html
Changes in v5:
- https://www.redhat.com/archives/dm-devel/2016-February/msg00112.html
Documentation/device-mapper/dm-init.txt | 114 +
drivers/md/Kconfig | 10 +
drivers/md/Makefile | 4 +
drivers/md/dm-init.c| 308
drivers/md/dm-ioctl.c
