Date: Thu, 07 Dec 2000 11:54:08 +1030 From: Matthew Thyer <Matthew.Thyer@dsto.defence.gov.au> To: freebsd-questions@freebsd.org Subject: write(2) returns error saying read only filesystem when trying to write to a partition Message-ID: <3A2EE6B8.69624B48@dsto.defence.gov.au>
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Attached is scrub.c used to scrub a hard disk.
Examine the lines:
/* if ( (fd = open("/dev/da12s1c",O_RDWR)) < 0 ) { */
if ( (fd = open("/mnt/foo",O_RDWR)) < 0 ) {
If I newfs the 'a' partition of da12s1 (a is the same as 'c'), mount
it as /mnt, touch the file foo and then run the program it works fine.
If instead I open the c partition (as in the commented out line),
the open succeeds, the lseek succeeds but the writes fail with an
error saying read only filesystem.
Why ??
I want to scrub the whole disk, not just write to a file.
--
Matthew Thyer Phone: +61 8 8259 7249
Science Corporate Information Systems Fax: +61 8 8259 5537
Defence Science and Technology Organisation, Salisbury
PO Box 1500 Salisbury South Australia 5108
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name="scrub.c"
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filename="scrub.c"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/uio.h>
#include <unistd.h>
#define BUFSIZE 8192
main()
{
/* program to write 1's and 0's to disk */
off_t result;
long int i;
long int nwrite;
long int count;
int passes;
int fd;
char buf0[BUFSIZE], buf1[BUFSIZE];
/* initialize write buffers */
for (i=0; i < BUFSIZE; i++) {
buf0[i] = 0;
buf1[i] = 1;
}
/* if ( (fd = open("/dev/da12s1c",O_RDWR)) < 0 ) { */
if ( (fd = open("/mnt/foo",O_RDWR)) < 0 ) {
perror("open");
exit(1);
}
/* write alternating 1s and zeros to disk */
for (i = 1; i <= 5; i++) {
/* rewind to start file partition */
if ((result = lseek(fd, 0L, SEEK_SET)) != 0) {
perror("lseek");
exit(1);
}
count = 0L;
do {
if ( (nwrite = write(fd, buf0, BUFSIZE)) != BUFSIZE) {
printf("wrote last %ld bytes to disk\n",nwrite);
printf("Total bytes written were %ld bytes\n",
BUFSIZE*count + nwrite);
perror("write");
}
else {
++count;
if ( count % 1000 == 0)
printf("overwrote %ld bytes w/ 0s\n",
BUFSIZE*count);
}
} while ( nwrite == BUFSIZE && nwrite > 0 );
/* rewind to start file partition */
if ((result = lseek(fd, 0L, SEEK_SET)) != 0) {
perror("lseek");
exit(1);
}
count = 0L;
do {
if ( (nwrite = write(fd, buf1, BUFSIZE)) != BUFSIZE) {
printf("wrote last %ld bytes to disk\n",nwrite);
printf("Total bytes written were %ld bytes\n",
BUFSIZE*count + nwrite);
perror("write");
}
else {
++count;
if ( count % 1000 == 0)
printf("overwrote %ld bytes w/ 1s\n",
BUFSIZE*count);
}
} while ( nwrite == BUFSIZE && nwrite > 0 );
printf("Pass %d complete\n",i);
}
printf("All passes complete\n");
}
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