In order to avoid closing standard streams multiple times, commit
52aa1a661 (include/closestream: avoid close more than once, 2019-06-13)
introduced code to set the standard output and error streams to `NULL`.
As musl libc defines standard streams as constant pointers, the change
causes compiler errors on systems with that libc. According to ISO C89,
being able to assign to the standard text streams is not a requirement
for any C implementation, see footnote 238 in chapter §7.19.5.6:
The primary use of the freopen function is to change the file
associated with a standard text stream (stderr, stdin, or stdout),
as those identifiers need not be modifiable lvalues to which the
value returned by the fopen function may be assigned.
This commit implements a new function `flush_standard_stream` that tries
to reliably flush standard streams without actually closing them. By not
calling fclose(3P), we can neatly avoid the issue of accessing standard
streams in an unspecified state and thus remove the infringing `NULL`
assignments.
Properly flushing standard streams without fclose(3P) proves to be more
intricate than one may expect, though, as some filesystems like NFS may
defer flushing until they see a close(3P) of the underlying descriptor.
One may call fsync(3P) to remedy that, but this may incur a heavy
performance penalty in some scenarios. To work around the issue and
still get proper errors, we duplicate the stream's file descriptor and
close that one instead, which is sufficient to cause a flush.
Note that both `close_stdout` and `close_stdout_atexit` are misnamed
after this change, as we do not actually close the streams now. In order
to avoid unnecessary code churn, we still retain their current names.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
It seems better to have a way to control when atexit(close_stdout()) is
used, because close stdout means that for example ASAN (or another
into binary integrated tool) is not able to print the final summary.
Signed-off-by: Karel Zak <kzak@redhat.com>
Exclude __fpending() from build when function is not available. This is
more obvious than adding a dummy function and expecting compiler to
eliminate it as dead code.
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
Essentially this helper function is similar to close_stream(), but for
file descriptors.
When a file descriptors are close()'d status of write is often
overlooked. The close_fd() will try to determine what happen to writes
with fsync() before closing the file descriptor.
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
Frantisek Sumsal
Patrick Steinhardt
Karel Zak
Sami Kerola