The test_overrides() test must be run first, otherwise we'll already
likely not have a clean environment to test in. Furthermore, when
testing discovery, make sure that NOIMPLICIT is not set.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

test_perf was still relying on the old behaviour of ul_openlog(): no
more, it uses ul_set_log_flags() now.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

Moved some tests around between test_umberlog and
test_umberlog_preload, so only those tests remain in
test_umberlog_preload that do test something that the LD_PRELOAD lib
variant provides.

Also added a comment above each test to quickly clarify what they're
meant to test.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

Based on a suggestion by Miloslav Trmač <mitr@redhat.com>, rename
LOG_UL_NODISCOVER to LOG_UL_NOIMPLICIT, and clarify the documentation
slightly.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

When compiled with --disable-discovery, the LD_PRELOAD variant will
have automatic field discovery disabled. This does not affect the
linkable library, which always has them enabled by default.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

Instead of piggy-backing on ul_openlog(), and accepting new flags at
openlog()-time, use a separate function, ul_set_log_flags() to achieve
the same.

This way, anyone who wants to flip any of the new flags, will have to
use ul_set_log_flags(), as ul_openlog() ignores them from now on.

This is based on work done by Miloslav Trmač <mitr@redhat.com>, and is
both an API and an ABI breakage.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

In order to satisfy the desire of using libumberlog, specifically
ul_format(), without having to worry about syslog() & friends being
overridden, split the library into two parts:

A linkable library, which provides the new API, but does not override
the legacy syslog() functions; and a new, LD_PRELOAD-able part, which
does override the old ones.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

Signed-off-by: Gergely Nagy <algernon@balabit.hu>

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

This simplifies the syslog() path a little, and allows us to express
"host name should be cached but no value is set.".

Because host name field is already emptied by default and in closelog (),
this also means uncached data is used before openlog () and after
closelog ().

Signed-off-by: Miloslav Trmač <mitr@redhat.com>