Beispiel #1
0
// mmap memory maps a DB's data file.
func mmap(db *DB, sz int) error {
	// Truncate and fsync to ensure file size metadata is flushed.
	// https://github.com/boltdb/bolt/issues/284
	if !db.NoGrowSync && !db.readOnly {
		if err := db.file.Truncate(int64(sz)); err != nil {
			return fmt.Errorf("file resize error: %s", err)
		}
		if err := db.file.Sync(); err != nil {
			return fmt.Errorf("file sync error: %s", err)
		}
	}

	// Map the data file to memory.
	b, err := unix.Mmap(int(db.file.Fd()), 0, sz, syscall.PROT_READ, syscall.MAP_SHARED|db.MmapFlags)
	if err != nil {
		return err
	}

	// Advise the kernel that the mmap is accessed randomly.
	if err := unix.Madvise(b, syscall.MADV_RANDOM); err != nil {
		return fmt.Errorf("madvise: %s", err)
	}

	// Save the original byte slice and convert to a byte array pointer.
	db.dataref = b
	db.data = (*[maxMapSize]byte)(unsafe.Pointer(&b[0]))
	db.datasz = sz
	return nil
}
Beispiel #2
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func TestMmap(t *testing.T) {
	b, err := unix.Mmap(-1, 0, unix.Getpagesize(), unix.PROT_NONE, unix.MAP_ANON|unix.MAP_PRIVATE)
	if err != nil {
		t.Fatalf("Mmap: %v", err)
	}
	if err := unix.Munmap(b); err != nil {
		t.Fatalf("Munmap: %v", err)
	}
}
Beispiel #3
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func mmap(name string) ([]byte, error) {
	file, err := os.Open(name)
	if err != nil {
		return nil, err
	}
	defer file.Close()
	stat, err := file.Stat()
	if err != nil {
		return nil, err
	}
	return unix.Mmap(int(file.Fd()), 0, int(stat.Size()), unix.PROT_EXEC|unix.PROT_WRITE|unix.PROT_READ, unix.MAP_PRIVATE)
}
Beispiel #4
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func mmap(f *os.File, offset int64, length int) ([]byte, error) {
	mmap, err := unix.Mmap(int(f.Fd()), 0, length, syscall.PROT_READ, syscall.MAP_SHARED)
	if err != nil {
		return nil, err
	}

	if err := unix.Madvise(mmap, syscall.MADV_RANDOM); err != nil {
		return nil, err
	}

	return mmap, nil
}
Beispiel #5
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// mmap the given file, get the mincore vector, then
// return it as an []bool
func FileMincore(f *os.File, size int64) ([]bool, error) {
	//skip could not mmap error when the file size is 0
	if int(size) == 0 {
		return nil, nil
	}
	// mmap is a []byte
	mmap, err := unix.Mmap(int(f.Fd()), 0, int(size), unix.PROT_NONE, unix.MAP_SHARED)
	if err != nil {
		return nil, fmt.Errorf("could not mmap: %v", err)
	}
	// TODO: check for MAP_FAILED which is ((void *) -1)
	// but maybe unnecessary since it looks like errno is always set when MAP_FAILED

	// one byte per page, only LSB is used, remainder is reserved and clear
	vecsz := (size + int64(os.Getpagesize()) - 1) / int64(os.Getpagesize())
	vec := make([]byte, vecsz)

	// get all of the arguments to the mincore syscall converted to uintptr
	mmap_ptr := uintptr(unsafe.Pointer(&mmap[0]))
	size_ptr := uintptr(size)
	vec_ptr := uintptr(unsafe.Pointer(&vec[0]))

	// use Go's ASM to submit directly to the kernel, no C wrapper needed
	// mincore(2): int mincore(void *addr, size_t length, unsigned char *vec);
	// 0 on success, takes the pointer to the mmap, a size, which is the
	// size that came from f.Stat(), and the vector, which is a pointer
	// to the memory behind an []byte
	// this writes a snapshot of the data into vec which a list of 8-bit flags
	// with the LSB set if the page in that position is currently in VFS cache
	ret, _, err := unix.Syscall(unix.SYS_MINCORE, mmap_ptr, size_ptr, vec_ptr)
	if ret != 0 {
		return nil, fmt.Errorf("syscall SYS_MINCORE failed: %v", err)
	}
	defer unix.Munmap(mmap)

	mc := make([]bool, vecsz)

	// there is no bitshift only bool
	for i, b := range vec {
		if b%2 == 1 {
			mc[i] = true
		} else {
			mc[i] = false
		}
	}

	return mc, nil
}
Beispiel #6
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// mmap memory maps a DB's data file.
func mmap(db *DB, sz int) error {
	// Map the data file to memory.
	b, err := unix.Mmap(int(db.file.Fd()), 0, sz, syscall.PROT_READ, syscall.MAP_SHARED|db.MmapFlags)
	if err != nil {
		return err
	}

	// Advise the kernel that the mmap is accessed randomly.
	if err := unix.Madvise(b, syscall.MADV_RANDOM); err != nil {
		return fmt.Errorf("madvise: %s", err)
	}

	// Save the original byte slice and convert to a byte array pointer.
	db.dataref = b
	db.data = (*[maxMapSize]byte)(unsafe.Pointer(&b[0]))
	db.datasz = sz
	return nil
}
Beispiel #7
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func mmap(fd int, length int) (data []byte, err error) {
	return unix.Mmap(fd, 0, length, syscall.PROT_READ, syscall.MAP_SHARED)
}
Beispiel #8
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func (m *mmap) mapFile() error {
	var err error
	m.buf, err = unix.Mmap(int(m.src.Fd()), 0, int(m.sz), unix.PROT_READ, unix.MAP_SHARED)
	return err
}