Previously when a log message grew beyond the maximum AF_UNIX/SOCK_DGRAM
datagram limit we'd send an fd to a deleted file in /dev/shm instead.
Because the sender could still modify the file after delivery we had to
immediately copy the data on the receiving side.
With memfds we can optimize this logic, and also remove the dependency
on /dev/shm: simply send a sealed memfd around, and if we detect the
seal memory map the fd and use it directly.
safe_close() automatically becomes a NOP when a negative fd is passed,
and returns -1 unconditionally. This makes it easy to write lines like
this:
fd = safe_close(fd);
Which will close an fd if it is open, and reset the fd variable
correctly.
By making use of this new scheme we can drop a > 200 lines of code that
was required to test for non-negative fds or to reset the closed fd
variable afterwards.
Current glibc implementation is safe. Kernel does this atomically,
and write is actually implemented through writev. So if write is
async-signal-safe, than writev pretty much must be too.
signal(7) provides a list of functions which may be called from a
signal handler. Other functions, which only call those functions and
don't access global memory and are reentrant are also safe.
sd_j_sendv was mostly OK, but would call mkostemp and writev in a
fallback path, which are unsafe.
Being able to call sd_j_sendv in a async-signal-safe way is important
because it allows it be used in signal handlers.
Safety is achieved by replacing mkostemp with open(O_TMPFILE) and an
open-coded writev replacement which uses write. Unfortunately,
O_TMPFILE is only available on kernels >= 3.11. When O_TMPFILE is
unavailable, an open-coded mkostemp is used.
https://bugzilla.gnome.org/show_bug.cgi?id=722889
"syslog(3) and sd_journal_print() may largely be used interchangeably
functionality-wise" according to sd_journal_print(3). This socket
should be always available except in rare circumstatances, and we
don't random applications to fail on logging, so let's do what syslog
did. The alternative of forcing all callers to do error handling for
this rare case doesn't really have any benefits, since if they can't
log there isn't much they can do anyway.
https://bugzilla.redhat.com/show_bug.cgi?id=1023041
I'm assuming that it's fine if a _const_ or _pure_ function
calls assert. It is assumed that the assert won't trigger,
and even if it does, it can only trigger on the first call
with a given set of parameters, and we don't care if the
compiler moves the order of calls.
../src/journal/journal-send.c: In function 'sd_journal_sendv':
../src/journal/journal-send.c:250:73: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
This splits the JSON output mode into different modes: json and
json-pretty. The former printing one entry per line, the latter showing
JSON objects nicely indented and in multiple lines to make it easier to
read for humans.
We finally got the OK from all contributors with non-trivial commits to
relicense systemd from GPL2+ to LGPL2.1+.
Some udev bits continue to be GPL2+ for now, but we are looking into
relicensing them too, to allow free copy/paste of all code within
systemd.
The bits that used to be MIT continue to be MIT.
The big benefit of the relicensing is that closed source code may now
link against libsystemd-login.so and friends.
This logic can be turned off by defining SD_JOURNAL_SUPPRESS_LOCATION
before including sd-journal.h.
This also saves/restores errno in all logging functions, in order to be
useful as logging calls without side-effects.
This also adds a couple of __unlikely__ around the early checks in the
logging calls, in order to minimize the runtime impact.
