Re: [Qemu-devel] [PATCH V3 3/3] linux-user: make host_to_target_cmsg support SO_TIMESTAMP cmsg_type

[Peter Maydell]

On 21 July 2012 02:30, Jing Huang <address@hidden> wrote:

This version of the patch is pretty close to correct -- just a few
minor things to fix...

>
> Signed-off-by: Jing Huang <address@hidden>
> ---
>  linux-user/syscall.c |   15 +++++++++++--
>  1 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 2228b1f..7521746 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -1350,8 +1350,17 @@ static inline abi_long host_to_target_cmsg(struct 
> target_msghdr *target_msgh,

Something weird happened here -- I couldn't apply this patch unless
I edited it by hand to say "+1350,19" in this diff hunk header.
You didn't edit the mail by hand after creating the diff, did you?

>          target_cmsg->cmsg_len = tswapal(TARGET_CMSG_LEN(len));
>
>          if (cmsg->cmsg_level != TARGET_SOL_SOCKET || cmsg->cmsg_type != 
> SCM_RIGHTS) {
> -            gemu_log("Unsupported ancillary data: %d/%d\n", 
> cmsg->cmsg_level, cmsg->cmsg_type);
> -            memcpy(target_data, data, len);
> +            if ((cmsg->cmsg_type == SO_TIMESTAMP) &&
> +                                    (len == sizeof(struct timeval))) {
> +                /* copy struct timeval to target */
> +                struct timeval *tv = (struct timeval *)data;
> +                struct timeval *target_tv = (struct timeval *)target_data;

This should be "struct target_timeval *target_tv" -- the timeval
struct is (on Linux) a pair of 'long's so it is laid out differently
for different target architectures.

(I had not realised this when commenting on earlier versions of this
patch; it does mean that this patch is the right way to do this,
because copying 32 bit integers would not handle the case of guest
and host having different 'long' sizes.)

> +
> +                tv->tv_sec = tswap32(target_tv->tv_sec);
> +                tv->tv_usec = tswap32(target_tv->tv_usec);
> +            } else {
> +                gemu_log("Unsupported ancillary data: %d/%d\n",
> +                                            cmsg->cmsg_level, 
> cmsg->cmsg_type);
> +                memcpy(target_data, data, len);
> +            }
>          } else {
>              int *fd = (int *)data;
>              int *target_fd = (int *)target_data;

The logic here isn't laid out quite right: you have
  if (not SCM rights) {
     if (timestamp) {
        handle timestamp;
     } else {
        complain;
     }
  } else {
     handle SCM rights;
  }

and what you want is:
  if (SCM rights) {
     handle SCM rights;
  } else if (timestamp) {
     handle timestamp;
  } else {
     complain;
  }

(which has the same effect but is much easier to read and understand).

Also, your check for "is this a timestamp" should include
a check that cmsg_level is TARGET_SOL_SOCKET.

-- PMM