The display of the /proc/PID/ns renders very wide. Make it
narrower by eliminating some nonessential info via some
awk(1) filtering.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Andrei Vagin implemented a change I suggested:
clock-IDs are now be expressed in symbolic form (e.g.,
"monotonic") instead of numeric form (e.g., 1) when reading
/proc/PID/timerns_offsets, and can be expressed either
symbolically or numerically when writing to that file.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
In particular, note the ERANGE restrictions reported by
Thomas Gleixner.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
signal.7: Which signal is delivered in response to a CPU exception
is under-documented and does not always make sense. See
<https://bugzilla.kernel.org/show_bug.cgi?id=205831> for an
example where it doesn’t make sense; per the discussion there,
this cannot be changed because of backward compatibility concerns,
so let’s instead document the problem.
sigaction.2: For related reasons, the kernel doesn’t always fill
in all of the fields of the siginfo_t when delivering signals from
CPU exceptions. Document this as well. I imagine this one
_could_ be fixed, but the problem would still be relevant to
anyone using an older kernel.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The example is misleading. It is not a good idea to unlink an
existing socket because we might try to start the server multiple
times. In this case it is preferable to receive an error.
We could add code that removes the socket when the server process
is killed but that would stretch the example too far.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Note the kernel version that added SO_TIMESTAMPNS,
and (from the kernel commit) note tha SO_TIMESTAMPNS and
SO_TIMESTAMP are mutually exclusive.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
===========
DESCRIPTION
===========
I added a paragraph for ``SO_TIMESTAMP``, and modified the
paragraph for ``SIOCGSTAMP`` in relation to ``SO_TIMESTAMPNS``.
I based the documentation on the existing ``SO_TIMESTAMP``
documentation, and
on my experience using ``SO_TIMESTAMPNS``.
I asked a question on stackoverflow, which helped me understand
``SO_TIMESTAMPNS``:
https://stackoverflow.com/q/60971556/6872717
Testing of the feature being documented
=======================================
I wrote a simple server and client test.
In the client side, I connected a socket specifying
``SOCK_STREAM`` and ``"tcp"``.
Then I enabled timestamp in ns:
.. code-block:: c
int enable = 1;
if (setsockopt(sd, SOL_SOCKET, SO_TIMESTAMPNS, &enable,
sizeof(enable)))
goto err;
Then I prepared the msg header:
.. code-block:: c
char buf[BUFSIZ];
char cbuf[BUFSIZ];
struct msghdr msg;
struct iovec iov;
memset(buf, 0, ARRAY_BYTES(buf));
iov.iov_len = ARRAY_BYTES(buf) - 1;
iov.iov_base = buf;
msg.msg_name = NULL;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = cbuf;
msg.msg_controllen = ARRAY_BYTES(cbuf);
And got some times before and after receiving the msg:
.. code-block:: c
struct timespec tm_before, tm_recvmsg, tm_after, tm_msg;
clock_gettime(CLOCK_REALTIME, &tm_before);
usleep(500000);
clock_gettime(CLOCK_REALTIME, &tm_recvmsg);
n = recvmsg(sd, &msg, MSG_WAITALL);
if (n < 0)
goto err;
usleep(1000000);
clock_gettime(CLOCK_REALTIME, &tm_after);
After that I read the timestamp of the msg:
.. code-block:: c
struct cmsghdr *cmsg;
for (cmsg = CMSG_FIRSTHDR(&msg); cmsg;
cmsg = CMSG_NXTHDR(&msg, cmsg)) {
if (cmsg->cmsg_level == SOL_SOCKET &&
cmsg->cmsg_type == SO_TIMESTAMPNS) {
memcpy(&tm_msg, CMSG_DATA(cmsg), sizeof(tm_msg));
break;
}
}
if (!cmsg)
goto err;
And finally printed the results:
.. code-block:: c
double tdiff;
printf("%s\n", buf);
tdiff = timespec_diff_ms(&tm_before, &tm_recvmsg);
printf("tm_r - tm_b = %lf ms\n", tdiff);
tdiff = timespec_diff_ms(&tm_before, &tm_after);
printf("tm_a - tm_b = %lf ms\n", tdiff);
tdiff = timespec_diff_ms(&tm_before, &tm_msg);
printf("tm_m - tm_b = %lf ms\n", tdiff);
Which printed:
::
asdasdfasdfasdfadfgdfghfthgujty 6, 0;
tm_r - tm_b = 500.000000 ms
tm_a - tm_b = 1500.000000 ms
tm_m - tm_b = 18.000000 ms
System:
::
Linux debian 5.4.0-4-amd64 #1 SMP Debian 5.4.19-1 (2020-02-13) x86_64
GNU/Linux
gcc (Debian 9.3.0-8) 9.3.0
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Linux 5.6 added the new well-known VMADDR_CID_LOCAL for
local communication.
This patch explains how to use it and removes the legacy
VMADDR_CID_RESERVED no longer available.
Reviewed-by: Jorgen Hansen <jhansen@vmware.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Add a '.RE' macro to terminate the last .RS block.
There is no change in the output.
Signed-off-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
In many cases, these don't improve readability, and (when stacked)
they sometimes have the side effect of sometimes forcing text
to be justified within a narrow column range.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
PVS-Studio reports that in
char buf[8192];
/* ... */
nh = (struct nlmsghdr *) buf,
the pointer 'buf' is cast to a more strictly aligned pointer type.
This is undefined behaviour. One possible solution to make sure
that buf is correctly aligned is to declare buf as an array of
struct nlmsghdr. Other solutions include allocating the array on
the heap, use an union, or stdalign features. With this patch,
the buffer still contains 8192 bytes.
This was raised on Stack Overflow:
https://stackoverflow.com/questions/57745580/netlink-receive-buffer-alignment
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk