diff --git a/unix/dev_linux.go b/unix/dev_linux.go new file mode 100644 index 00000000..c902c39e --- /dev/null +++ b/unix/dev_linux.go @@ -0,0 +1,42 @@ +// Copyright 2017 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Functions to access/create device major and minor numbers matching the +// encoding used by the Linux kernel and glibc. +// +// The information below is extracted and adapted from bits/sysmacros.h in the +// glibc sources: +// +// dev_t in glibc is 64-bit, with 32-bit major and minor numbers. glibc's +// default encoding is MMMM Mmmm mmmM MMmm, where M is a hex digit of the major +// number and m is a hex digit of the minor number. This is backward compatible +// with legacy systems where dev_t is 16 bits wide, encoded as MMmm. It is also +// backward compatible with the Linux kernel, which for some architectures uses +// 32-bit dev_t, encoded as mmmM MMmm. + +package unix + +// Major returns the major component of a Linux device number. +func Major(dev uint64) uint32 { + major := uint32((dev & 0x00000000000fff00) >> 8) + major |= uint32((dev & 0xfffff00000000000) >> 32) + return major +} + +// Minor returns the minor component of a Linux device number. +func Minor(dev uint64) uint32 { + minor := uint32((dev & 0x00000000000000ff) >> 0) + minor |= uint32((dev & 0x00000ffffff00000) >> 12) + return minor +} + +// Mkdev returns a Linux device number generated from the given major and minor +// components. +func Mkdev(major, minor uint32) uint64 { + dev := uint64((major & 0x00000fff) << 8) + dev |= uint64((major & 0xfffff000) << 32) + dev |= uint64((minor & 0x000000ff) << 0) + dev |= uint64((minor & 0xffffff00) << 12) + return dev +} diff --git a/unix/dev_linux_test.go b/unix/dev_linux_test.go new file mode 100644 index 00000000..6e001f37 --- /dev/null +++ b/unix/dev_linux_test.go @@ -0,0 +1,51 @@ +// Copyright 2017 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package unix_test + +import ( + "fmt" + "testing" + + "golang.org/x/sys/unix" +) + +func TestDevices(t *testing.T) { + testCases := []struct { + path string + major uint32 + minor uint32 + }{ + // well known major/minor numbers according to + // https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/devices.txt + {"/dev/null", 1, 3}, + {"/dev/zero", 1, 5}, + {"/dev/random", 1, 8}, + {"/dev/full", 1, 7}, + {"/dev/urandom", 1, 9}, + {"/dev/tty", 5, 0}, + } + for _, tc := range testCases { + t.Run(fmt.Sprintf("%s %v:%v", tc.path, tc.major, tc.minor), func(t *testing.T) { + var stat unix.Stat_t + err := unix.Stat(tc.path, &stat) + if err != nil { + t.Errorf("failed to stat device: %v", err) + return + } + + dev := uint64(stat.Rdev) + if unix.Major(dev) != tc.major { + t.Errorf("for %s Major(%#x) == %d, want %d", tc.path, dev, unix.Major(dev), tc.major) + } + if unix.Minor(dev) != tc.minor { + t.Errorf("for %s Minor(%#x) == %d, want %d", tc.path, dev, unix.Minor(dev), tc.minor) + } + if unix.Mkdev(tc.major, tc.minor) != dev { + t.Errorf("for %s Mkdev(%d, %d) == %#x, want %#x", tc.path, tc.major, tc.minor, unix.Mkdev(tc.major, tc.minor), dev) + } + }) + + } +}