Between fork() and exec() in the child process it is only safe to use
async-signal-safe functions. Surprisingly, snprintf() is not such
function. See e.g. https://stackoverflow.com/a/6771799 and how snprintf
is not listed in signal-safety(7) manual.
Therefore we must prepare the fd argument strings before fork(). That is
only possible if we also do not dup() fd in the child process. Hence we
remove the close-on-exec flag instead in the child process which has
copies of the parent's file descriptors. Fortunately fcntl() is safe.
struct fdstr is helping to reduce code clutter a bit.
Additionally, if fork() fails, we now clean up the fds we created.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Pekka Paalanen
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