lkml.org 
[lkml]   [2001]   [Feb]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: rawio usage

Content-Type: multipart/mixed;
boundary="------------D4869FCB9AEAF2CC69FB9DEF"

This is a multi-part message in MIME format.
--------------D4869FCB9AEAF2CC69FB9DEF
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

"Mayank Vasa" <mvasa@confluencenetworks.com> wrote:
> I am quite new to rawio and am experimenting with with its usage. My test
> environment is Redhat 7.0, kernel version 2.2.16-22 having an external fibre
> channel drive having 2 disks (/dev/sda1 and /dev/sdb1)
>
> All I am trying to do is to write and read to & from the disk using a raw
> device. Externally I did a "raw /dev/raw/raw1 /dev/sdb1" and then I wrote a
> small program to do the read/write.

[snip]

Raw devices need to meet the alignment requirements of the
device they are bound to; in the case of most disk this
will be 512 bytes. You need to take this into account for:
- the buffer you give to the read() and write() calls
- the 'size' given to read() and write() should be a
multiple of 512
- the SEEK_SET 'offset' given to lseek() should be a
multiple of 512. Note you have a 2 G limit here.
You can use _llseek() to get around this.

A small program that just reads from a raw device (or the
corresponding block device which should give the same
result) attached.

If you were binding a raw device to a cdrom device then
the BLKSIZE would need to be 2048 bytes (in most cases).

Doug Gilbert
--------------D4869FCB9AEAF2CC69FB9DEF
Content-Type: text/plain; charset=us-ascii;
name="my_rawio_ex.c"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
filename="my_rawio_ex.c"

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

#define BLKSIZE 512
#define BLKS2READ 1

int main(int argc, char *argv[])
{
int fd, k;
unsigned char buff[BLKSIZE * (BLKS2READ + 1)]; // allow extra for alignment
unsigned char * arbp; // aligned read buffer ptr
long block_addr = 0;

arbp = (char *)(((unsigned long)buff + (BLKSIZE - 1)) & (~(BLKSIZE - 1)));

fd = open(argv[1], O_RDONLY);
if (fd < 0) {
perror("open");
exit (1);
}
if ((lseek(fd, block_addr * BLKSIZE, SEEK_SET)) < 0){
perror("lseek"); // problem if 2nd arg > 2G
exit (1);
}
if ((read(fd, arbp, BLKSIZE * BLKS2READ)) < 0) {
perror("read");
exit(1);
}

printf("First 16 bytes of the readbuf (in hex) are:\n ");
for (k = 0; k < 16; ++k)
printf("%x ", (int)arbp[k]);
printf("\n");
close(fd);
return 0;
}

--------------D4869FCB9AEAF2CC69FB9DEF--

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

\
 
 \ /
  Last update: 2005-03-22 13:17    [W:0.038 / U:1.592 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site