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1 // Copyright 2017 The Go Authors. All rights reserved.
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2 // Use of this source code is governed by a BSD-style
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3 // license that can be found in the LICENSE file.
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4
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5 // Functions to access/create device major and minor numbers matching the
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6 // encoding used by the Linux kernel and glibc.
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7 //
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8 // The information below is extracted and adapted from bits/sysmacros.h in the
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9 // glibc sources:
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10 //
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11 // dev_t in glibc is 64-bit, with 32-bit major and minor numbers. glibc's
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12 // default encoding is MMMM Mmmm mmmM MMmm, where M is a hex digit of the major
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13 // number and m is a hex digit of the minor number. This is backward compatible
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14 // with legacy systems where dev_t is 16 bits wide, encoded as MMmm. It is also
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15 // backward compatible with the Linux kernel, which for some architectures uses
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16 // 32-bit dev_t, encoded as mmmM MMmm.
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17
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18 package unix
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19
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20 // Major returns the major component of a Linux device number.
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21 func Major(dev uint64) uint32 {
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22 major := uint32((dev & 0x00000000000fff00) >> 8)
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23 major |= uint32((dev & 0xfffff00000000000) >> 32)
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24 return major
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25 }
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26
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27 // Minor returns the minor component of a Linux device number.
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28 func Minor(dev uint64) uint32 {
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29 minor := uint32((dev & 0x00000000000000ff) >> 0)
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30 minor |= uint32((dev & 0x00000ffffff00000) >> 12)
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31 return minor
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32 }
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33
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34 // Mkdev returns a Linux device number generated from the given major and minor
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35 // components.
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36 func Mkdev(major, minor uint32) uint64 {
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37 dev := (uint64(major) & 0x00000fff) << 8
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38 dev |= (uint64(major) & 0xfffff000) << 32
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39 dev |= (uint64(minor) & 0x000000ff) << 0
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40 dev |= (uint64(minor) & 0xffffff00) << 12
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41 return dev
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42 }
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