Re: [PATCH v20 13/14] log: add support for systemd journal

[Luca Boccassi <bluca@debian.org>]

On Sat, 30 Mar 2024 at 16:46, Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> If DPDK application is being run as a systemd service, then
> it can use the journal protocol which allows putting more information
> in the log such as priority and other information.
>
> The use of journal protocol is automatically detected and
> handled.  Rather than having a dependency on libsystemd,
> just use the protocol directly as defined in:
>         https://systemd.io/JOURNAL_NATIVE_PROTOCOL/
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  doc/guides/prog_guide/log_lib.rst   |  14 ++
>  lib/eal/common/eal_common_options.c |  11 ++
>  lib/eal/common/eal_options.h        |   2 +
>  lib/log/log.c                       |   5 +
>  lib/log/log_internal.h              |   3 +
>  lib/log/log_journal.c               | 200 ++++++++++++++++++++++++++++
>  lib/log/log_private.h               |   2 +
>  lib/log/log_stubs.c                 |  11 +-
>  lib/log/meson.build                 |  10 +-
>  lib/log/version.map                 |   1 +
>  10 files changed, 255 insertions(+), 4 deletions(-)
>  create mode 100644 lib/log/log_journal.c

This is very nice work, I like it a lot!

> +/*
> + * send structured message using journal protocol
> + * See: https://systemd.io/JOURNAL_NATIVE_PROTOCOL/
> + */
> +static int
> +journal_send(const char *buf, size_t len)
> +{
> +       struct iovec iov[4];
> +       unsigned int n = 0;
> +       int priority = rte_log_cur_msg_loglevel() - 1;
> +       char msg[] = "MESSAGE=";
> +       char newline = '\n';
> +       char pbuf[16];  /* "PRIORITY=N\n" */
> +
> +       iov[n].iov_base = msg;
> +       iov[n++].iov_len = strlen(msg);
> +
> +       iov[n].iov_base = (char *)(uintptr_t)buf;
> +       iov[n++].iov_len = len;
> +
> +       /* if message doesn't end with newline, one will be applied. */
> +       if (buf[len - 1] != '\n') {
> +               iov[n].iov_base = &newline;
> +               iov[n++].iov_len = 1;
> +       }
> +
> +       /* priority value between 0 ("emerg") and 7 ("debug") */
> +       iov[n].iov_base = pbuf;
> +       iov[n++].iov_len = snprintf(pbuf, sizeof(pbuf),
> +                                   "PRIORITY=%d\n", priority);
> +
> +       return writev(log_journal_fd, iov, n);
> +}

Doesn't need to be implemented immediately, but the nicest thing about
talking directly to the journal is the ability to send lots of
arbitrary and useful metadata together with a message, so would be
nice if the logging function took an optional string vector that is
appended, or some other such mechanism.

A very useful example is creating a UUID and then setting
MESSAGE_ID=uuid when logging particularly important messages that are
useful to filter by this type - for example, when an interface state
changes to up/down. That way, one can do 'journalctl MESSAGE_ID=abc..'
and get all messages about interface state changes. A project can also
ship a catalog file that adds additional context to each ID, that is
automatically parsed and displayed to users.