Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: File I/O from within a driver | Date | Wed, 25 May 2005 14:18:44 +0200 |
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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.
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