Hi,
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. The program is:
#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>
int main(int argc, char *argv[])
{
int fd;
char writeBuf[512];
char readBuf[100];
memset(readBuf, '\0', 100);
memset(writeBuf, '\0', 100);
memcpy(writeBuf, "This is a test", 14);
printf("writeBuf = %s\n", writeBuf);
fd = open(argv[1], O_RDWR);
if (fd < 0) {
perror("open");
exit (1);
}
if ((lseek(fd, 0L, 0)) < 0){
perror("lseek");
exit (1);
}
if ((write(fd, writeBuf, 512)) < 0) {
printf ("errno = %d\n", errno);
perror("write");
exit(1);
}
lseek(fd, 0L, 0);
if ((read(fd, readBuf, 512)) < 0) {
perror("read");
exit(1);
}
printf("The readbuf is %s\n", readBuf);
return 0;
}
When I run this program as root, I get the error "write: Invalid argument".
It is basically returning errno = 22 which is EINVAL and as per the write
manpage means that fd is attached to an object which is unsuitable for
writing.
Could someone guide me on where I am going wrong & how to use raw devices?
--
Mayank Vasa
Confluence Networks.
Hi,
On Mon, Feb 05, 2001 at 10:36:32PM -0800, Mayank Vasa wrote:
>
> When I run this program as root, I get the error "write: Invalid argument".
Raw IO requires that the buffers are aligned on a 512-byte boundary in
memory.
--Stephen
need 512 byte alignment
i.e.
change
char writeBuf[512];
to:
char writeBuf[1023];
writeBuf = (char *)(((int )&writeBuf[0] + 511) &~511);
This will typecast the writeBuffer address to an int and add 511 to the
address. When you and that with ~511( invert 511). That will result int
something in a multiple of 512 for the address.
Then just typecast it back.
That is how to align it. Jens Was kind enough to tell me how to do this.
Nathan
-----Original Message-----
From: Mayank Vasa [mailto:[email protected]]
Sent: Tuesday, February 06, 2001 1:37 AM
To: Linux-Kernel
Subject: rawio usage
Hi,
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. The program is:
#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>
int main(int argc, char *argv[])
{
int fd;
char writeBuf[512];
char readBuf[100];
memset(readBuf, '\0', 100);
memset(writeBuf, '\0', 100);
memcpy(writeBuf, "This is a test", 14);
printf("writeBuf = %s\n", writeBuf);
fd = open(argv[1], O_RDWR);
if (fd < 0) {
perror("open");
exit (1);
}
if ((lseek(fd, 0L, 0)) < 0){
perror("lseek");
exit (1);
}
if ((write(fd, writeBuf, 512)) < 0) {
printf ("errno = %d\n", errno);
perror("write");
exit(1);
}
lseek(fd, 0L, 0);
if ((read(fd, readBuf, 512)) < 0) {
perror("read");
exit(1);
}
printf("The readbuf is %s\n", readBuf);
return 0;
}
When I run this program as root, I get the error "write: Invalid argument".
It is basically returning errno = 22 which is EINVAL and as per the write
manpage means that fd is attached to an object which is unsuitable for
writing.
Could someone guide me on where I am going wrong & how to use raw devices?
--
Mayank Vasa
Confluence Networks.
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" <[email protected]> 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--