I ran into a problem today with the 2.6.0 release. This happened to
show up in the read04 LTP test, but not reliably. I have attached a
test program that I think does trigger it reliably, though.
When run on ext3:
/home/pcarns> ./testme /tmp/foo.txt
read returned: 7, test_buf: hello world
When run on pvfs2:
/home/pcarns> ./testme /mnt/pvfs2/foo.txt
read returned: 7, test_buf: hello
(or sometimes you might get garbage after the "hello")
The test program creates a string buffer with "goodbye world" stored in
it. It then reads the string "hello " out of a file into the beginning
of that buffer. The result should be that the final resulting string
is "hello world".
The trick that makes this fail is asking to read more than 7 bytes from
the file.
In this particular test program, we attempt to do a read of 255 bytes.
There are only 7 bytes in the file, though. The return code from read
accurately reflects this. However, rather than just fill in the first 7
bytes of the buffer, it looks like PVFS2 is overwriting the full 255
bytes. What ends up in those trailing 248 bytes is somewhat random.
I suspect that somewhere in the kernel module there is a copy_to_user()
call that is copying the number of bytes requested by the read rather
than the number of bytes returned by the servers.
-Phil
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char **argv)
{
int fd = 0;
int ret = 0;
char test_string[] = "hello ";
char test_buf[256];
if(argc != 2)
{
fprintf(stderr, "Usage: %s <filename>\n", argv[0]);
return(-1);
}
fd = open(argv[1], O_RDWR|O_CREAT|O_TRUNC, (S_IRUSR | S_IWUSR));
if(fd < 0)
{
perror("open");
return(-1);
}
ret = write(fd, test_string, strlen(test_string));
if(ret != strlen(test_string))
{
fprintf(stderr, "Error: write failed.\n");
return(-1);
}
/* put some garbage in the buffer so we can detect if something goes wrong */
strcpy(test_buf, "goodbye world");
lseek(fd, 0, SEEK_SET);
ret = read(fd, test_buf, 255);
printf("read returned: %d, test_buf: %s\n", ret, test_buf);
close(fd);
return(0);
}
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