PKGBUILD/vendor/periph.io/x/periph/host/pmem/pagemap.go

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2018-12-04 18:11:50 +00:00
// Copyright 2016 The Periph Authors. All rights reserved.
// Use of this source code is governed under the Apache License, Version 2.0
// that can be found in the LICENSE file.
package pmem
import (
"encoding/binary"
"errors"
"fmt"
"os"
)
// ReadPageMap reads a physical address mapping for a virtual page address from
// /proc/self/pagemap.
//
// It returns the physical address that corresponds to the start of the virtual
// page within which the virtual address virtAddr is located.
//
// The meaning of the return value is documented at
// https://www.kernel.org/doc/Documentation/vm/pagemap.txt
func ReadPageMap(virtAddr uintptr) (uint64, error) {
if !isLinux {
return 0, errors.New("pmem: pagemap is not supported on this platform")
}
return readPageMapLinux(virtAddr)
}
//
var (
pageMap fileIO
pageMapErr error
)
func readPageMapLinux(virtAddr uintptr) (uint64, error) {
var b [8]byte
mu.Lock()
defer mu.Unlock()
if pageMap == nil && pageMapErr == nil {
// Open /proc/self/pagemap.
//
// It is a uint64 array where the index represents the virtual 4Kb page
// number and the value represents the physical page properties backing
// this virtual page.
pageMap, pageMapErr = openFile("/proc/self/pagemap", os.O_RDONLY|os.O_SYNC)
}
if pageMapErr != nil {
return 0, pageMapErr
}
// Convert address to page number, then index in uint64 array.
offset := int64(virtAddr / pageSize * 8)
if _, err := pageMap.Seek(offset, os.SEEK_SET); err != nil {
return 0, fmt.Errorf("pmem: failed to seek at 0x%x for 0x%x: %v", offset, virtAddr, err)
}
n, err := pageMap.Read(b[:])
if err != nil {
return 0, fmt.Errorf("pmem: failed to read at 0x%x for 0x%x: %v", offset, virtAddr, err)
}
if n != len(b) {
return 0, fmt.Errorf("pmem: failed to read the amount of data %d", len(b))
}
return binary.LittleEndian.Uint64(b[:]), nil
}