mmap()

mmap()

[niamathullah sharief]

HelloCan anyone tell me how this mmap() works,how its creates the buffer and how its storing the video in that buffer..can anyone explain as algorithm with mmap() and ioctl() functions with their parameters...Thanks..


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mmap()

[niamathullah sharief]

Hello,   Actually what is mmap()?why it used?shall we write the program without that function?


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Re: mmap()

[niamathullah sharief]

micheal..you are telling that read() function will do the same as the mmap() does..but the read() will read the data from the memory i think....is this ,,ap() is also doing the same one?if yes....how its actually the data (when capturing the video) was stored in memory....?
--- On Fri, 23/1/09, Michael Williamson <michael_h_williamson@yahoo.com> wrote:
From: Michael Williamson <michael_h_williamson@yahoo.com>
Subject: Re: mmap()
To: shariefbe@yahoo.co.in
Date: Friday, 23 January, 2009, 10:28 PM



--- On Fri, 1/23/09, niamathullah sharief <shariefbe@yahoo.co.in> wrote:

> From: niamathullah sharief <shariefbe@yahoo.co.in>
> Subject: mmap()
> To: "video4linux list" <video4linux-list@redhat.com>,
"Kernel newbies" <kernelnewbies@nl.linux.org>, "micheal
williams" <michael_h_williamson@yahoo.com>
> Date: Friday, January 23, 2009, 7:14 AM
> Hello,   Actually what is mmap()?why it used?shall we
> write the program without that function?



The mmap() function makes the memory containing
the picture pixel data available to the program.

The alternative is to use the read() function,
to get the picture pixel data. I do not have
a program that does it that way. 

It is possible to get picture pixel data from a 
camera from the shell prompt like this:

   # head -c 304128 /dev/video0 > pict.raw

That does the same things as open() and 
read() functions do using a 'C' program.


-Mike







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Re: mmap()

[niamathullah sharief]

micheal..you are telling that read() function will do the
 same as the mmap() does...so this both function are reading the data from the memory location...am i right?...if yes how the data exist there?after catching the video whether the data stored in default free location are any othere mapping function is there to store theat captured data?

--- On Sat, 24/1/09, Michael Williamson <michael_h_williamson@yahoo.com> wrote:
From: Michael Williamson <michael_h_williamson@yahoo.com>
Subject: Re: mmap()
To: shariefbe@yahoo.co.in
Date: Saturday, 24 January, 2009, 12:53 AM



--- On Fri, 1/23/09, niamathullah sharief <shariefbe@yahoo.co.in> wrote:

> From: niamathullah sharief <shariefbe@yahoo.co.in>
> Subject: Re: mmap()
> To: michael_h_williamson@yahoo.com, "video4linux list"
<video4linux-list@redhat.com>, "Kernel newbies"
<kernelnewbies@nl.linux.org>
> Date: Friday, January 23, 2009, 12:41 PM
> micheal..you are telling that read() function will do the
> same as the mmap() does..but the read() will read the data
> from the memory i think....is this ,,ap() is also doing the
> same one?if yes....how its actually the data (when capturing
> the video) was stored in memory....?



I do not understand your question.

-Mike



      



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Re: mmap()

[niamathullah sharief]

ok micheal...Thanks..actually when we capture the video from webcam how that video is captured and where it stores?and how it finds the memory location to store that captured data?



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