Add a simple mmap wrapper for cross-platform mmap usage

Win32 has a variant of mmap that is harder to use than POSIX, but
to run natively and efficiently on Win32 we need some form of it.

gitfo_map_ro() provides a basic mmap function for use in locations
where we need read-only random data access to large ranges of a file,
such as a pack-*.idx.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/fileops.c b/src/fileops.c
index 16b9dc520..f494e4772 100644
--- a/src/fileops.c
+++ b/src/fileops.c
@@ -1,5 +1,6 @@
 #include "common.h"
 #include "fileops.h"
+#include <sys/mman.h>
 
 int gitfo_open(const char *path, int flags)
 {
@@ -106,6 +107,20 @@ void gitfo_free_buf(gitfo_buf *obj)
 	obj->data = NULL;
 }
 
+int gitfo_map_ro(gitfo_map *out, git_file fd, off_t begin, size_t len)
+{
+	out->data = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, begin);
+	if (out->data == (void*)-1)
+		return git_os_error();
+	out->len = len;
+	return GIT_SUCCESS;
+}
+
+void gitfo_free_map(gitfo_map *out)
+{
+	munmap(out->data, out->len);
+}
+
 /* cached diskio */
 struct gitfo_cache {
 	git_file fd;