Hi Michael
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));
The #ifdef CONFIG_CHECKPOINT_RESTORE only affected prepare_copy function
and the EINVAL judgment is not included in #ifdef.
So, if current kernel config disables CONFIG_CHECKPOINT_RESTORE, Using
MSG_COPY without IPC_NOWAIT will still hit EINVAL error firstly and
doesn't run into prepare_copy function to hit ENOSYS error.
Best Regards
Yang Xu
...
}
]]
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
