This adds a new safe_fork() wrapper around fork() and makes use of it
everywhere. The new wrapper does a couple of things we previously did
manually and separately in a safer, more correct and automatic way:
1. Optionally resets signal handlers/mask in the child
2. Sets a name on all processes we fork off right after forking off (and
the patch assigns useful names for all processes we fork off now,
following a systematic naming scheme: always enclosed in () – in order
to indicate that these are not proper, exec()ed processes, but only
forked off children, and if the process is long-running with only our
own code, without execve()'ing something else, it gets am "sd-" prefix.)
3. Optionally closes all file descriptors in the child
4. Optionally sets a PR_SET_DEATHSIG to SIGTERM in the child, in a safe
way so that the parent dying before this happens being handled
safely.
5. Optionally reopens the logs
6. Optionally connects stdin/stdout/stderr to /dev/null
7. Debug logs about the forked off processes.
In the future we might want to allow additional syntax (for example
"unset VAR". But let's check that the data we're getting does not contain
anything unexpected.
The output of processes can be gathered, and passed back to the callee.
(This commit just implements the basic functionality and tests.)
After the preparation in previous commits, the change in functionality is
relatively simple. For coding convenience, alarm is prepared *before* any
children are executed, and not before. This shouldn't matter usually, since
just forking of the children should be pretty quick. One could also argue that
this is more correct, because we will also catch the case when (for whatever
reason), forking itself is slow.
Three callback functions and three levels of serialization are used:
- from individual generator processes to the generator forker
- from the forker back to the main process
- deserialization in the main process
v2:
- replace an structure with an indexed array of callbacks
Essentially the same logic as in conf_files_list() was independently implemented in
do_execute(). With previous commit, do_execute() can just call conf_files_list() to
get a list of executable paths.
