win32: Add routines to abstract memory-mapped file functions

In particular, the git__mmap() and git__munmap() routines provide
the interface to platform specific memory-mapped file facilities.
We provide implementations for unix and win32, which can be found
in their own sub-directories.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 125 insertions, 0 deletions

diff --git a/src/win32/map.c b/src/win32/map.c
new file mode 100644
index 000000000..7d685c722
--- /dev/null
+++ b/src/win32/map.c
@@ -0,0 +1,125 @@
+
+#include "map.h"
+#include <errno.h>
+
+
+static DWORD get_page_size(void)
+{
+	static DWORD page_size;
+	SYSTEM_INFO sys;
+
+	if (!page_size) {
+		GetSystemInfo(&sys);
+		page_size = sys.dwAllocationGranularity;
+	}
+
+	return page_size;
+}
+
+int git__mmap(git_map *out, size_t len, int prot, int flags, int fd, off_t offset)
+{
+	HANDLE fh = (HANDLE)_get_osfhandle(fd);
+	DWORD page_size = get_page_size();
+	DWORD fmap_prot = 0;
+	DWORD view_prot = 0;
+	DWORD off_low = 0;
+	DWORD off_hi  = 0;
+	off_t page_start;
+	off_t page_offset;
+
+	assert((out != NULL) && (len > 0));
+
+	if ((out == NULL) || (len == 0)) {
+		errno = EINVAL;
+		return GIT_ERROR;
+	}
+
+	out->data = NULL;
+	out->len = 0;
+	out->fmh = NULL;
+
+	if (fh == INVALID_HANDLE_VALUE) {
+		errno = EBADF;
+		return GIT_ERROR;
+	}
+
+	if (prot & GIT_PROT_WRITE)
+		fmap_prot |= PAGE_READWRITE;
+	else if (prot & GIT_PROT_READ)
+		fmap_prot |= PAGE_READONLY;
+	else {
+		errno = EINVAL;
+		return GIT_ERROR;
+	}
+
+	if (prot & GIT_PROT_WRITE)
+		view_prot |= FILE_MAP_WRITE;
+	if (prot & GIT_PROT_READ)
+		view_prot |= FILE_MAP_READ;
+
+	if (flags & GIT_MAP_FIXED) {
+		errno = EINVAL;
+		return GIT_ERROR;
+	}
+
+	page_start = (offset / page_size) * page_size;
+	page_offset = offset - page_start;
+
+	if (page_offset != 0) {  /* offset must be multiple of page size */
+		errno = EINVAL;
+		return GIT_ERROR;
+	}
+
+	out->fmh = CreateFileMapping(fh, NULL, fmap_prot, 0, 0, NULL);
+	if (!out->fmh || out->fmh == INVALID_HANDLE_VALUE) {
+		/* errno = ? */
+		out->fmh = NULL;
+		return GIT_ERROR;
+	}
+
+	off_low = (DWORD)(page_start);
+	if (sizeof(off_t) > 4)
+		off_hi = (DWORD)(page_start >> 32);
+	out->data = MapViewOfFile(out->fmh, view_prot, off_hi, off_low, len);
+	if (!out->data) {
+		/* errno = ? */
+		CloseHandle(out->fmh);
+		out->fmh = NULL;
+		return GIT_ERROR;
+	}
+	out->len = len;
+
+	return GIT_SUCCESS;
+}
+
+int git__munmap(git_map *map)
+{
+	assert(map != NULL);
+
+	if (!map)
+		return GIT_ERROR;
+
+	if (map->data) {
+		if (!UnmapViewOfFile(map->data)) {
+			/* errno = ? */
+			CloseHandle(map->fmh);
+			map->data = NULL;
+			map->fmh = NULL;
+			return GIT_ERROR;
+		}
+		map->data = NULL;
+	}
+
+	if (map->fmh) {
+		if (!CloseHandle(map->fmh)) {
+			/* errno = ? */
+			map->fmh = NULL;
+			return GIT_ERROR;
+		}
+		map->fmh = NULL;
+	}
+
+	return GIT_SUCCESS;
+}
+
+