Hello Yang Xu,
On Wed, 9 Sep 2020 at 05:57, Yang Xu <xuyang2018.jy@xxxxxxxxxxxxxx> wrote:
>
> When calling msgrcv with MSG_COPY flag on 3.8 or new kernel, it will
> report EINVAL error even we have disabled CONFIG_CHECKPOINT_RESTORE.
> It also needs to specify IPC_NOWAIT flag.
>
> Signed-off-by: Yang Xu <xuyang2018.jy@xxxxxxxxxxxxxx>
> ---
> man2/msgop.2 | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/man2/msgop.2 b/man2/msgop.2
> index 373e53aa7..e559097a7 100644
> --- a/man2/msgop.2
> +++ b/man2/msgop.2
> @@ -467,7 +467,9 @@ and the queue contains less than
> messages.
> .TP
> .BR ENOSYS " (since Linux 3.8)"
> -.I MSG_COPY
> +.B IPC_NOWAIT
> +and
> +.B MSG_COPY
> was specified in
> .IR msgflg ,
> and this kernel was configured without
> --
> 2.23.0
My apologies, I have a little bit of trouble to understand your commit
message, but the patch does seem to be wrong, at least as I understand
the code:
[[
#ifdef CONFIG_CHECKPOINT_RESTORE
...
#else
static inline struct msg_msg *prepare_copy(void __user *buf, size_t bufsz)
{
return ERR_PTR(-ENOSYS);
}
...
static long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long
msgtyp, int msgflg,
long (*msg_handler)(void __user *, struct msg_msg *, size_t))
{
...
if (msgflg & MSG_COPY) {
if ((msgflg & MSG_EXCEPT) || !(msgflg & IPC_NOWAIT))
return -EINVAL;
copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax));
...
}
]]
My reading of that code is:
if MSG_COPY && MSG_EXCEPT ==> EINVAL
if MSG_COPY && ! IPC_NOWAIT ==> EINVAL
if neither of the above: if MSG_COPY && ! CONFIG_CHECKPOINT_RESTORE ==> ENOSYS
And all of that seems already to be captured in the manual page:
EINVAL (since Linux 3.14)
msgflg specified MSG_COPY, but not IPC_NOWAIT.
EINVAL (since Linux 3.14)
msgflg specified both MSG_COPY and MSG_EXCEPT.
ENOSYS (since Linux 3.8)
MSG_COPY was specified in msgflg, and this kernel was con‐
figured without CONFIG_CHECKPOINT_RESTORE.
Have I missed something?
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
