Interpose `open` library function

`open` is not as side effect free as I had imagined - i.e. if the flag `O_TRUNC` is passed it truncates the file contents alongside opening the file descriptor. In practice this is done by _emacs_ prior to writing the new file content and as such needs to be intercepted so we can start tracking the file before it is changed.

Interposing `open` required some changes to make the library work without including `fcntl.h`. This header not only defines some of the flags we require to check if a library call actually is able to change files but also defines the `open` library function.

While implementing this change I noticed that the function interpositions implemented in C++ actually need to be declared as `external "C"` so their names do not get wrangled during compilation. I suspect that this was previously implicitly done for e.g. `mmap` and `write` by the included C standard library headers. However this did not work for `open` which is why all function interpositions are now explicitly declared external.

End result: _emacs_ file changes are now tracked correctly.

1 files changed, 0 insertions, 3 deletions

diff --git a/src/actual.h b/src/actual.h
index a860590..ae951b9 100644
--- a/src/actual.h
+++ b/src/actual.h
@@ -6,9 +6,6 @@
 #endif
 
 #include <dlfcn.h>
-#include <sys/mman.h>
-#include <sys/uio.h>
-
 #include <memory>
 #include <cstring>