github.com/bir3/gocompiler@v0.9.2202/src/xvendor/golang.org/x/sys/unix/dev_linux.go (about)

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