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>
pull/236/head
Johannes Schindelin 7 years ago committed by Junio C Hamano
parent 7ce7ee2d82
commit d5425d10ca
  1. 16
      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) {

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