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>
Johannes Schindelin committed
Apr 22, 2016 at 16:31 UTC
d5425d10ca68a297061f87f4460dd7e0b32b39a6
1 file changed
+7
-9
compat/win32mmap.c
+7
-9
@@ -2,26 +2,24 @@
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void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t offset)
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{
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- HANDLE hmap;
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+ HANDLE osfhandle, hmap;
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void *temp;
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- off_t len;
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- struct stat st;
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+ LARGE_INTEGER len;
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uint64_t o = offset;
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uint32_t l = o & 0xFFFFFFFF;
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uint32_t h = (o >> 32) & 0xFFFFFFFF;
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- if (!fstat(fd, &st))
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- len = st.st_size;
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- else
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+ osfhandle = (HANDLE)_get_osfhandle(fd);
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+ if (!GetFileSizeEx(osfhandle, &len))
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die("mmap: could not determine filesize");
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- if ((length + offset) > len)
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- length = xsize_t(len - offset);
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+ if ((length + offset) > len.QuadPart)
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+ length = xsize_t(len.QuadPart - offset);
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if (!(flags & MAP_PRIVATE))
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die("Invalid usage of mmap when built with USE_WIN32_MMAP");
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- hmap = CreateFileMapping((HANDLE)_get_osfhandle(fd), NULL,
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+ hmap = CreateFileMapping(osfhandle, NULL,
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prot == PROT_READ ? PAGE_READONLY : PAGE_WRITECOPY, 0, 0, NULL);
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if (!hmap) {