lkml.org 
[lkml]   [2005]   [May]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: File I/O from within a driver
Date
On Middeweken 25 Mai 2005 07:15, van wrote:
>  The structure of media files is complex and I'd rather the calling application
>  didn't need to have any knowledge of that structure.  But how can the driver
>  do the necessary read() operations?
>  
> I could, for example, have the application pass an open file descriptor in to
> my driver via an ioctl() call; if I understand matters correctly, my driver
> could then call sys_read().  I've never done anything like that before, never
> expected to need to, and it doesn't feel right.

_if_ you want to read the file, use fget() and vfs_read() on the file
descriptor you get passed. It is however considered rather bad style to
do file I/O from drivers. As Brian Gerst said, better use mmap in user
space and pass the pointer via ioctl() or write().

> Can anyone suggest the *proper* way to accomplish this?

Your assumption that the driver should parse the media file structure
is probably wrong. You should rather do as much as possible in a user
space library. Pass a file name to a library call and have that
work with all the complex parts of the file format, then define an
ioctl interface for the driver on a relatively low level.

Or even better, don't use ioctl() at all but implement only read()/write()
in the driver. E.g. for MPEG acceleration, you might want to have an
interface where you write a series of macro blocks to the character
device and read back pixel data.

Arnd <><
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-05-25 14:42    [W:0.090 / U:0.268 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site