Mailing List Archive: Linux: Kernel

v4l device in userspace

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antirez at gmail

Jun 16, 2006, 4:03 AM

Post #1 of 5 (196 views)
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v4l device in userspace

Hello, I'm trying to implement a v4l device driver
for symbian based smart phones. In theory
it is very simple:

I've a little program running in the phone, capturing
images from the camera and sending it to the
linux box via bluetooth.

In the linux box side, I've a deamon capturing this
images (via a bluetooth SP channel), and....
I've to pass the images to a fake v4l device
driver that actually gets the images form userspace.

Basically I've to pass by the kernel just for
the interface, and not to do real kernel-side work
(like to access to the some kind of hardware).

So I've some questions ( thanks in advance
for any reply).

1) What's the best way to pass relatively
high-band data between the v4l fake driver
and userspace? A char device will do the
work? ioctl?

2) What about some way to handle ioctl
directly from userspace? Given this support
I may implement the whole code in userspace.
And I guess there are a lot of other real world
problems that can be handled in userspace
given the ability to handle ioctl from there.

If you think 2) is reasonable I may actually
implement some simple form of generic
char driver that just allows userspace
programs to handle read/write/ioctl
opreations, and then use this to fix
my real issue.

Thank you very much for the help,
and sorry if there is something conceptually
wrong in my questions.

Regards,
Salvatore

P.S. please take me in CC as I'm not subscribed
to the linux kernel mailing list.

--
Salvatore 'antirez' Sanfilippo
We're programmers. Programmers are, in their hearts, architects -- Joel Spolsky
http://www.invece.org
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mocm at mocm

Jun 16, 2006, 4:46 AM

Post #2 of 5 (186 views)
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v4l device in userspace [In reply to]

>>>>> "Salvatore" == Salvatore Sanfilippo <antirez [at] gmail> writes:

Salvatore> Hello, I'm trying to implement a v4l device driver for
Salvatore> symbian based smart phones. In theory it is very
Salvatore> simple:

Salvatore> I've a little program running in the phone, capturing
Salvatore> images from the camera and sending it to the linux box
Salvatore> via bluetooth.

Salvatore> In the linux box side, I've a deamon capturing this
Salvatore> images (via a bluetooth SP channel), and.... I've to
Salvatore> pass the images to a fake v4l device driver that
Salvatore> actually gets the images form userspace.

Salvatore> Basically I've to pass by the kernel just for the
Salvatore> interface, and not to do real kernel-side work (like to
Salvatore> access to the some kind of hardware).

Salvatore> So I've some questions ( thanks in advance for any
Salvatore> reply).

Salvatore> 1) What's the best way to pass relatively high-band
Salvatore> data between the v4l fake driver and userspace? A char
Salvatore> device will do the work? ioctl?

Salvatore> 2) What about some way to handle ioctl directly from
Salvatore> userspace? Given this support I may implement the whole
Salvatore> code in userspace. And I guess there are a lot of
Salvatore> other real world problems that can be handled in
Salvatore> userspace given the ability to handle ioctl from there.

Salvatore> If you think 2) is reasonable I may actually implement
Salvatore> some simple form of generic char driver that just
Salvatore> allows userspace programs to handle read/write/ioctl
Salvatore> opreations, and then use this to fix my real issue.

Salvatore> Thank you very much for the help, and sorry if there is
Salvatore> something conceptually wrong in my questions.

Sounds like you should take a look at the v4l loopback device
(http://www.lavrsen.dk/twiki/bin/view/Motion/VideoFourLinuxLoopbackDevice).
Otherwise it may be better to ask the question on the v4l mailing list
(https://listman.redhat.com/mailman/listinfo/video4linux-list).

Anyway, since you already capture the video, why do you have to pipe
it through a v4l device?

Marcus

--
/--------------------------------------------------------------------\
| Dr. Marcus O.C. Metzler | |
| mocm [at] metzlerbros | http://www.metzlerbros.de/ |
\--------------------------------------------------------------------/
|>>> Quis custodiet ipsos custodes <<<|
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antirez at gmail

Jun 16, 2006, 4:57 AM

Post #3 of 5 (191 views)
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Re: v4l device in userspace [In reply to]

On 6/16/06, Marcus Metzler <mocm [at] mocm> wrote:

> Sounds like you should take a look at the v4l loopback device

Thanks this may contain useful code indeed.

> Anyway, since you already capture the video, why do you have to pipe
> it through a v4l device?

In order to make every application using the v4l API
working with the phone cam without modifications.

Thanks,
Salvatore

--
Salvatore 'antirez' Sanfilippo
We're programmers. Programmers are, in their hearts, architects -- Joel Spolsky
http://www.invece.org
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mkrufky at linuxtv

Jun 16, 2006, 7:18 AM

Post #4 of 5 (186 views)
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Re: v4l device in userspace [In reply to]

Salvatore Sanfilippo wrote:
> Hello, I'm trying to implement a v4l device driver
> for symbian based smart phones. In theory
> it is very simple:
>
> I've a little program running in the phone, capturing
> images from the camera and sending it to the
> linux box via bluetooth.
>
> In the linux box side, I've a deamon capturing this
> images (via a bluetooth SP channel), and....
> I've to pass the images to a fake v4l device
> driver that actually gets the images form userspace.
>
> Basically I've to pass by the kernel just for
> the interface, and not to do real kernel-side work
> (like to access to the some kind of hardware).
>
> So I've some questions ( thanks in advance
> for any reply).
>
> 1) What's the best way to pass relatively
> high-band data between the v4l fake driver
> and userspace? A char device will do the
> work? ioctl?
>
> 2) What about some way to handle ioctl
> directly from userspace? Given this support
> I may implement the whole code in userspace.
> And I guess there are a lot of other real world
> problems that can be handled in userspace
> given the ability to handle ioctl from there.
>
> If you think 2) is reasonable I may actually
> implement some simple form of generic
> char driver that just allows userspace
> programs to handle read/write/ioctl
> opreations, and then use this to fix
> my real issue.
>
> Thank you very much for the help,
> and sorry if there is something conceptually
> wrong in my questions.
>
> Regards,
> Salvatore
>
> P.S. please take me in CC as I'm not subscribed
> to the linux kernel mailing list.
>
I recommend resubmitting this question to a mailing list that actually
focuses on this topic:

video4linux-list [at] redhat

However, I highly recommend that you subscribe before you post, as the
redhat server adds a REPLY-TO header to the video4linux list emails, and
has been known to drop cc's:

http://www.redhat.com/mailman/listinfo/video4linux-list

See you there!

-Michael Krufky

--
Michael Krufky

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pavel at ucw

Jun 19, 2006, 2:57 PM

Post #5 of 5 (187 views)
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Re: v4l device in userspace [In reply to]

Hi!

> I've a little program running in the phone, capturing
> images from the camera and sending it to the
> linux box via bluetooth.

Nice!

> Basically I've to pass by the kernel just for
> the interface, and not to do real kernel-side work
> (like to access to the some kind of hardware).
>
> So I've some questions ( thanks in advance
> for any reply).
>
> 1) What's the best way to pass relatively
> high-band data between the v4l fake driver
> and userspace? A char device will do the
> work? ioctl?
>
> 2) What about some way to handle ioctl
> directly from userspace? Given this support
> I may implement the whole code in userspace.
> And I guess there are a lot of other real world
> problems that can be handled in userspace
> given the ability to handle ioctl from there.
>
> If you think 2) is reasonable I may actually
> implement some simple form of generic
> char driver that just allows userspace
> programs to handle read/write/ioctl
> opreations, and then use this to fix
> my real issue.

You probably want to do something v4l specigic... but generic userspace driver
able to do read/write/ioctl would be very nice. Lots of devices these days are on usb, and that can be done from userspace, for example.
Pavel
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