fdio: Add cleanup+flush API for FILE*

Mostly in ostree/rpm-ostree, we work in either raw `int fd`, or
`G{Input,Output}Stream`.  One exception is the rpm-ostree `/etc/passwd`
handling, which uses `FILE*` since that's what glibc exposes.

And in general, there are use cases for `FILE*`; the raw `GUnixOutputStream` for
example isn't buffered, and doing so via e.g. `GBufferedOutputStream` means
allocating *two* GObjects and even worse going through multiple vfuncs for every
write.

`FILE*` is used heavily in systemd, and provides buffering. It is a bit cheaper
than gobjects, but has its own trap; by default every operation locks a mutex.
For more information on that, see `unlocked_stdio(3)`. However, callers can
avoid that by using e.g. `fwrite_unlocked`, which I plan to do for most users of
`FILE*` that aren't writing to one of the standard streams like `stdout` etc.

1 files changed, 17 insertions, 0 deletions

diff --git a/glnx-fdio.h b/glnx-fdio.h
index f459e93..150b22e 100644
--- a/glnx-fdio.h
+++ b/glnx-fdio.h
@@ -50,6 +50,23 @@ const char *glnx_basename (const char *path)
   return (basename) (path);
 }
 
+/* Utilities for standard FILE* */
+static inline void
+glnx_stdio_file_cleanup (void *filep)
+{
+  FILE *f = filep;
+  if (f)
+    fclose (f);
+}
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(FILE, glnx_stdio_file_cleanup)
+
+/**
+ * glnx_stdio_file_flush:
+ * Call fflush() and check ferror().
+ */
+gboolean
+glnx_stdio_file_flush (FILE *f, GError **error);
+
 typedef struct {
   gboolean initialized;
   gboolean anonymous;