mmap(win32): avoid expensive fstat() call

On Windows, we have to emulate the fstat() call to fill out information
that takes extra effort to obtain, such as the file permissions/type.

If all we want is the file size, we can use the much cheaper
GetFileSizeEx() function (available since Windows XP).

Suggested by Philip Kelley.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/compat/win32mmap.c b/compat/win32mmap.c
index b836169..519d51f 100644 (file)
--- a/compat/win32mmap.c
+++ b/compat/win32mmap.c
@@ -2,26 +2,24 @@
 
 void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset)
 {
-       HANDLE hmap;
+       HANDLE osfhandle, hmap;
        void *temp;
-       off_t len;
-       struct stat st;
+       LARGE_INTEGER len;
        uint64_t o = offset;
        uint32_t l = o & 0xFFFFFFFF;
        uint32_t h = (o >> 32) & 0xFFFFFFFF;
 
-       if (!fstat(fd, &st))
-               len = st.st_size;
-       else
+       osfhandle = (HANDLE)_get_osfhandle(fd);
+       if (!GetFileSizeEx(osfhandle, &len))
                die("mmap: could not determine filesize");
 
-       if ((length + offset) > len)
-               length = xsize_t(len - offset);
+       if ((length + offset) > len.QuadPart)
+               length = xsize_t(len.QuadPart - offset);
 
        if (!(flags & MAP_PRIVATE))
                die("Invalid usage of mmap when built with USE_WIN32_MMAP");
 
-       hmap = CreateFileMapping((HANDLE)_get_osfhandle(fd), NULL,
+       hmap = CreateFileMapping(osfhandle, NULL,
                prot == PROT_READ ? PAGE_READONLY : PAGE_WRITECOPY, 0, 0, NULL);
 
        if (!hmap) {