On Tue, 2005-01-18 at 18:31, Sami Farin wrote:
> On Tue, Jan 18, 2005 at 05:22:44PM -0800, Daniel McNeil wrote:
> > Andrew,
> >
> > This is a patch to generic_file_buffered_write() to correctly
> > handle partial O_DIRECT writes (because of unallocated blocks)
> > when there is more than 1 iovec. Without this patch, the code is
> > writing the wrong iovec (it writes the first iovec a 2nd time).
> >
> > Included is a test program dio_bug.c that shows the problem by:
> > writing 4k to offset 4k
> > writing 4k to offset 12k
> > writing 8k to offset 4k
> > The result is that 8k write writes the 1st 4k of the buffer twice.
> >
> > $ rm f; ./dio_bug f
> > wrong value offset 8k expected 0x33 got 0x11
> > wrong value offset 10k expected 0x44 got 0x22
> >
> > with patch
> > $ rm f; ./dio_bug f
>
> I have Linux 2.6.10-ac9 + bio clone memory corruption -patch,
> and dio_bug does not give errors (without your patch).
I should have mentioned that my testing was on ext3 with 4k
block size. The bio clone patch might affect this by merging
the i/o into a single iovec. Here's an updated test program
that uses 2 different buffers allocated separately that might
prevent the merging. See if this works on your system.
#define _GNU_SOURCE
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/uio.h>
main(int argc, char **argv)
{
int fd;
char *buf;
char *buf2;
int i;
struct iovec v[2];
fd = open(argv[1], O_DIRECT|O_RDWR|O_CREAT, 0666);
if (fd < 0) {
perror("open");
exit(1);
}
buf = valloc(8192);
buf2 = valloc(8192);
lseek(fd, 0x1000, SEEK_SET);
memset(buf, 0x11, 2048);
memset(buf+2048, 0x22, 2048);
i = write(fd, buf, 4096); /* 4k write of 0x11 and 0x22 at 4k */
lseek(fd, 0x3000, SEEK_SET);
memset(buf, 0x55, 2048);
memset(buf+2048, 0x66, 2048);
i = write(fd, buf, 4096); /* 4k write of 0x55 and 0x66 at 12k */
lseek(fd, 0x1000, SEEK_SET);
i = read(fd, buf, 4096);
memset(buf2, 0x33 , 2048);
memset(buf2+2048, 0x44 , 2048);
v[0].iov_base = buf;
v[0].iov_len = 4096;
v[1].iov_base = buf2;
v[1].iov_len = 4096;
lseek(fd, 0x1000, SEEK_SET);
i = writev(fd, v, 2); /* 8k write of 0x11, 0x22, 0x33, 0x44 at 4k */
lseek(fd, 0x2000, SEEK_SET);
i = read(fd, buf, 4096);
if (buf[0] != 0x33)
printf("wrong value offset 8k expected 0x33 got 0x%x\n",
buf[0]);
if (buf[2048] != 0x44)
printf("wrong value offset 10k expected 0x44 got 0x%x\n",
buf[2048]);
}
Thanks,
Daniel
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