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)
}
}
// munmap unmaps a DB's data file from memory.
func munmap(db *DB) error {
// Ignore the unmap if we have no mapped data.
if db.dataref == nil {
return nil
}
// Unmap using the original byte slice.
err := unix.Munmap(db.dataref)
db.dataref = nil
db.data = nil
db.datasz = 0
return err
}
// 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
}
func munmap(b []byte) (err error) {
return unix.Munmap(b)
}
// Close releases the shared object file and invalidates the patch.
func (p *Patch) Close() error {
return unix.Munmap(p.obj)
}
func (m *mmap) unmap() error {
return unix.Munmap(m.buf)
}