Hi,
On Wed, 9 Nov 2005, Paulo da Silva wrote:
> I posted about this a few days ago but got no responses
> so far! I think this should be a trivial question for those
> involved in the kernel internals. May be I didn't develop
> the problem enough to be understood.
>
> So, here is the question reformulated.
>
> A given file system must supply a procedure for mmap.
>
> int <fsname>_file_mmap(struct file * file, struct vm_area_struct * vma)
> {
> int addr;
> addr=generic_file_mmap(file,vma);
> <Code to access addr pointed bytes or vma->vm_start>
> return addr;
> }
>
> I could verify that "addr" is what is returned to the user as
> a pointer to a string of bytes that maps a file when a user
> program calls mmap or mmap2.
>
> In the user program, I can access those bytes (read/write)
> as, for ex., a char pointer.
>
> I don't know how to access those bytes inside the kernel
> at the point <Code to access addr pointed bytes or vma->vm_start>
>
> First trys led the program that invoked mmap to block.
> I thought that there's something to do with a previous
> down_write(¤t->mm->mmap_sem);
> If I execute
> up_write(¤t->mm->mmap_sem);
> before accessing the data the block situation does not
> occur anymore. I would like to hear something about
> this.
>
> Anyway, I tryed to use "copy_from_user" but I got
> garbage, not the file contents! Using "strncpy" crashes
> the kernel (UML)!
>
> Can someone please write a fragment of code to safely
> access those bytes, copying them to and from a
> kernel char pointed area so that they are read/written
> to the file?
Why do you want to do that? If you explain what you are trying to do it
may be possible to help you better. It is almost 100% certain that your
are going about it in completely the wrong way, so please describe what
you are trying to do...
Best regards,
Anton
--
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
