Messages in this thread |  | | From | Nathan Black <> | Subject | RE: rawio usage | Date | Tue, 6 Feb 2001 09:48:00 -0500 |
| |
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:mvasa@confluencenetworks.com] 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.
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