[dm-devel] setting up dmverity using device mapper IOCTLs

[dm-devel] setting up dmverity using device mapper IOCTLs

[Pra.. Dew..]

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Hello,

I need to setup dm-verity from my program-basically mount verity enabled filesystems from my code. I have looked at veritysetup and devicemapper (libdm) library. I was wondering if there is some simple C code to use the DM IOCTLs directly to setup verity. Any guidance to directly use the dm IOCTLs or libdm would also be helpful. Thank you for the guidance.

Thanks


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[dm-devel] Location for the definition of dm_task

[Pra.. Dew..]

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I see that in libdevmapper.c<https://gitlab.com/cryptsetup/cryptsetup/-/blob/master/lib/libdevmapper.c#L266> following line is defined

struct dm_task *dmt;

I cannot seem to find out where is dm_task and associated functions are actually defined? I do not see them in the libdevmapper library headers and .c files. Thank you for all the guidance.

Thanks



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Re: [dm-devel] Location for the definition of dm_task

[Zdenek Kabelac]

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Dne 12. 09. 22 v 7:55 Pra.. Dew.. napsal(a):
>
> I see that in libdevmapper.c 
> <https://gitlab.com/cryptsetup/cryptsetup/-/blob/master/lib/libdevmapper.c#L266> 
> following line is defined
>
> struct||dm_task|*|dmt|;|
>
> ||
>
> |I cannot seem to find out where is dm_task and associated functions are 
> actually defined? I do not see them in the libdevmapper library headers and 
> .c files. Thank you for all the guidance.|
>

Hi


This structure is private to libdevmapper only usage.  Access to struct 
members is provided only via  public functions.

You  can always look at source files  - libdm/ioctl/libdm-targets.h  -  but as 
mentioned earlier - forget about using a copy of this struct in your tools - 
there is only public access - as the structure content may freely change 
between release of libdevmapper - which would have made you binary incompatible.


Regards


Zdenek


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Re: [dm-devel] setting up dmverity using device mapper IOCTLs

[Zdenek Kabelac]

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Dne 10. 09. 22 v 20:46 Pra.. Dew.. napsal(a):
>
> Hello,
>
> I need to setup dm-verity from my program-basically mount verity enabled 
> filesystems from my code. I have looked at veritysetup and devicemapper 
> (libdm) library. I was wondering if there is some simple C code to use the 
> DM IOCTLs directly to setup verity. Any guidance to directly use the dm 
> IOCTLs or libdm would also be helpful. Thank you for the guidance.
>

Hi

I'd recommend  to exec "dmsetup"  call - as that's by far the simplest 
solution for your problem.

Verity tool should supposedly solve 'compatibility' between various versions 
and various capabilities of driver.

What is the idea behind redevelopment of this tool by your  C code  (as 
clearly you should then do the same thing as verity tool)  ?


Regards


Zdenek

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Re: [dm-devel] setting up dmverity using device mapper IOCTLs

[Pra.. Dew..]

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Thank you Zdenek. We are developing a embedded system with very constrained memory/storage. So we are trying to see if we can combine utilities like dmsetup with other Rust code for managing storage in our embedded system, while only including the parts of dmsetup that we really need. Hence I am trying to figure out what is the best way here.

Thanks

From: Zdenek Kabelac<mailto:zkabelac@redhat.com>
Sent: Monday, September 12, 2022 6:01 AM
To: Pra.. Dew..<mailto:linux_learner@outlook.com>; dm-devel@redhat.com<mailto:dm-devel@redhat.com>
Subject: Re: [dm-devel] setting up dmverity using device mapper IOCTLs

Dne 10. 09. 22 v 20:46 Pra.. Dew.. napsal(a):
Hello,

I need to setup dm-verity from my program-basically mount verity enabled filesystems from my code. I have looked at veritysetup and devicemapper (libdm) library. I was wondering if there is some simple C code to use the DM IOCTLs directly to setup verity. Any guidance to directly use the dm IOCTLs or libdm would also be helpful. Thank you for the guidance.




Hi

I'd recommend  to exec "dmsetup"  call - as that's by far the simplest solution for your problem.

Verity tool should supposedly solve 'compatibility' between various versions and various capabilities of driver.

What is the idea behind redevelopment of this tool by your  C code  (as clearly you should then do the same thing as verity tool)  ?



Regards



Zdenek


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Re: [dm-devel] setting up dmverity using device mapper IOCTLs

[Bryn M. Reeves]

On Mon, Sep 12, 2022 at 03:37:19PM +0000, Pra.. Dew.. wrote:
> Thank you Zdenek. We are developing a embedded system with very constrained memory/storage. So we are trying to see if we can combine utilities like dmsetup with other Rust code for managing storage in our embedded system, while only including the parts of dmsetup that we really need. Hence I am trying to figure out what is the best way here.

If you are working with Rust then you may want to evaluate the
devicemapper-rs library:

  https://github.com/stratis-storage/devicemapper-rs/

This is an implementation of a high level interface to the DM ioctls in
Rust - it obtains some constants from libdevmapper.h via bindgen but the
ioctl handling and header parsing is done natively.

It's been around for a while and is used by Stratis and some other
projects. There have been a few discussions around a new userspace DM
implementation in Rust with a somewhat different interface but nothing
has been written so far.

Regards,
Bryn.

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