Re: Unable to read/write in kernel module

[Erik Mouw <mouw@xxxxxxxxxxxx>]

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On Mon, Dec 18, 2006 at 10:21:01AM -0800, Junhan Zhang (junhan) wrote:
> I read the FAQ. Technically, it is right, but useless.8-( 

You're right, reading/writing from kernel is indeed useless :)

> I have a kernel module to do the statistic for compactflash partition
> 1, and have to save to partition 2. 

I have no idea what you mean with "do the statistic for partition 1",
but if you want to know what reads/writes to that partition, have a
look at Jens Axboe's blktrace (see Google).

> I am using kernel 2.6.11 .Do you have any good idea to do it?

Sure, add a device to your module, then have a userspace program that
basically boils down to:

  int infd, outfd;
  char buf[BUFLEN];
  int got;

  infd = open("/dev/mydevice", O_RDONLY);
  outfd = open("/mnt/secondpartition/outfile", O_WRONLY | O_CREAT, 0666);

  while((got = read(infd, buf, BUFLEN)) > 0) {
          write(outfd, buf, got);
  }

  /* something went wrong */
  if(got < 0) {
          perror("read(infd)");
          exit(1);
  }

  close(outfd);
  close(infd);

Needs some more error handling, but you got my point.
(yeah, that code looks a lot like cat, cp, and dd :)

Support for blktrace got merged in 2.6.18, IIRC (it most certainly is
in 2.6.19.1). If blktrace gives enough information, you can do anything
you need in userland.


Erik

-- 
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