libutil: Add a helper for O_TMPFILE + mmap()

I added `glnx_open_anonymous_tmpfile()`, but then later noticed
that the usage of this was really to be combined with `mmap()`,
and we had two versions of that in the delta code.  Add a helper.

(Bigger picture...how is this different from glibc's "mmap() of /dev/zero"
 approach for large chunks? One advantage is the storage can be "swapped" to
 `/var/tmp`, but still deleted automatically, rather than requiring swap space)

Closes: #973
Approved by: jlebon

1 files changed, 5 insertions, 0 deletions

diff --git a/src/libotutil/ot-fs-utils.h b/src/libotutil/ot-fs-utils.h
index 3b40d337..43bc6942 100644
--- a/src/libotutil/ot-fs-utils.h
+++ b/src/libotutil/ot-fs-utils.h
@@ -86,6 +86,11 @@ gboolean ot_dfd_iter_init_allow_noent (int dfd,
                                        gboolean *out_exists,
                                        GError **error);
 
+GBytes *
+ot_map_anonymous_tmpfile_from_content (GInputStream *instream,
+                                       GCancellable *cancellable,
+                                       GError      **error);
+
 GBytes *ot_file_mapat_bytes (int dfd,
                              const char *path,
                              GError **error);