Re: [PATCH] Fix traceaio with IO_CMD_{PREAD,PWRITE}

[Nir Soffer <nsoffer@redhat.com>]

On Thu, Sep 23, 2021 at 8:49 PM Nir Soffer <nsoffer@redhat.com> wrote:
>
> When using IO_CMD_{PREAD,PWRITE} aio_nbytes is the size of a single
> buffer aio_buf.
>
> Previously the script logged unrelated memory contents from userspace:
>
> [     0 sanlock(8214):] io_submit(140589225578496, 1, 0x7fdd5fefc718)
>     iocb[   0]=0x7fdd58000b70, fd=16, opcode=0, offset=0, nbytes=1048576, buf=0x7fdd5c5f6000
>         iovec[   0]=0x7fdd5c5f6000, base=0x3000412212010, len=16
>         iovec[   1]=0x7fdd5c5f6010, base=0x0, len=1
>         iovec[   2]=0x7fdd5c5f6020, base=0x1, len=16
>         ...
>
> Now we trace iovecs only when using IO_CMD_{PREADV,PWITEV}:
>
> [     0 sanlock(8397):] io_submit(140589225566208, 1, 0x7fdd5e6f9718)
>     iocb[   0]=0x7fdd48000b70, fd=19, opcode=0, offset=0, nbytes=1048576, buf=0x7fdd5c3f2000
> [     0 sanlock(8397):] io_submit(140589225566208, 1, 0x7fdd5e6f9718)
>     iocb[   0]=0x7fdd48000b70, fd=19, opcode=1, offset=512, nbytes=512, buf=0x7fdd4810a000
>
> Signed-off-by: Nir Soffer <nsoffer@redhat.com>
> ---
>  testsuite/systemtap.examples/io/traceaio.stp | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/testsuite/systemtap.examples/io/traceaio.stp b/testsuite/systemtap.examples/io/traceaio.stp
> index 126ea9c3c..903d65526 100755
> --- a/testsuite/systemtap.examples/io/traceaio.stp
> +++ b/testsuite/systemtap.examples/io/traceaio.stp
> @@ -8,6 +8,9 @@
>  # published by the Free Software Foundation.
>  #
>
> +@define IO_CMD_PREADV   %( 7 %)
> +@define IO_CMD_PWRITEV  %( 8 %)

Unfortunately this does not work. I tested this before adding these "constants".

This works:

global IO_CMD_PREADV = 7
global IO_CMD_PWRITEV = 8

Do we have a better way to handle this?

> +
>  probe begin {
>      println("Tracing started");
>  }
> @@ -27,12 +30,14 @@ probe syscall.io_submit
>              printf("    iocb[%4d]=%p, fd=%d, opcode=%d, offset=%d, nbytes=%d, buf=%p\n",
>                     i, iocbp, fd, opcode, offset, nbytes, buf)
>
> -            for (j = 0; j < nbytes; j++) {
> -                iovecp = &@cast(buf, "iovec", "kernel")[j]
> -                base = user_uint64(&@cast(iovecp, "iovec", "kernel")->iov_base)
> -                len = user_uint32(&@cast(iovecp, "iovec", "kernel")->iov_len)
> -                printf("        iovec[%4d]=%p, base=%p, len=%d\n",
> -                       j, iovecp, base, len)
> +            if (opcode == @IO_CMD_PREADV || opcode == @IO_CMD_PREADV) {
> +                for (j = 0; j < nbytes; j++) {
> +                    iovecp = &@cast(buf, "iovec", "kernel")[j]
> +                    base = user_uint64(&@cast(iovecp, "iovec", "kernel")->iov_base)
> +                    len = user_uint32(&@cast(iovecp, "iovec", "kernel")->iov_len)
> +                    printf("        iovec[%4d]=%p, base=%p, len=%d\n",
> +                           j, iovecp, base, len)
> +                }
>              }
>          }
>      }
> --
> 2.31.1
>