42 lines
1.5 KiB
Go
42 lines
1.5 KiB
Go
// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Functions to access/create device major and minor numbers matching the
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// encoding used by the Linux kernel and glibc.
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//
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// The information below is extracted and adapted from bits/sysmacros.h in the
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// glibc sources:
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//
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// dev_t in glibc is 64-bit, with 32-bit major and minor numbers. glibc's
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// default encoding is MMMM Mmmm mmmM MMmm, where M is a hex digit of the major
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// number and m is a hex digit of the minor number. This is backward compatible
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// with legacy systems where dev_t is 16 bits wide, encoded as MMmm. It is also
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// backward compatible with the Linux kernel, which for some architectures uses
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// 32-bit dev_t, encoded as mmmM MMmm.
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package unix
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// Major returns the major component of a Linux device number.
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func Major(dev uint64) uint32 {
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major := uint32((dev & 0x00000000000fff00) >> 8)
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major |= uint32((dev & 0xfffff00000000000) >> 32)
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return major
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}
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// Minor returns the minor component of a Linux device number.
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func Minor(dev uint64) uint32 {
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minor := uint32((dev & 0x00000000000000ff) >> 0)
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minor |= uint32((dev & 0x00000ffffff00000) >> 12)
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return minor
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}
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// Mkdev returns a Linux device number generated from the given major and minor
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// components.
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func Mkdev(major, minor uint32) uint64 {
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dev := (uint64(major) & 0x00000fff) << 8
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dev |= (uint64(major) & 0xfffff000) << 32
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dev |= (uint64(minor) & 0x000000ff) << 0
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dev |= (uint64(minor) & 0xffffff00) << 12
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return dev
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}
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