1 | <sect2>
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2 | <title>Why we copy the kernel headers and don't symlink them</title>
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3 |
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4 | <para>In the past, it was common practice for people to symlink the
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5 | /usr/include/linux and asm directories to /usr/src/linux/include/linux
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6 | and asm respectively. This is a <emphasis>bad</emphasis> idea as
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7 | this extract from a post by Linus Torvalds to the Linux Kernel
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8 | Mailing List points out:</para>
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9 |
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10 | <screen>I would suggest that people who compile new kernels should:
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11 |
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12 | - not have a single symbolic link in sight (except the one that the
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13 | kernel build itself sets up, namely the "linux/include/asm" symlink
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14 | that is only used for the internal kernel compile itself)
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15 |
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16 | And yes, this is what I do. My /usr/src/linux still has the old 2.2.13
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17 | header files, even though I haven't run a 2.2.13 kernel in a _loong_
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18 | time. But those headers were what glibc was compiled against, so those
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19 | headers are what matches the library object files.
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20 |
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21 | And this is actually what has been the suggested environment for at
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22 | least the last five years. I don't know why the symlink business keeps
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23 | on living on, like a bad zombie. Pretty much every distribution still
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24 | has that broken symlink, and people still remember that the linux
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25 | sources should go into "/usr/src/linux" even though that hasn't been
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26 | true in a _loong_ time.</screen>
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27 |
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28 | <para>The relevant part here is where he states that the headers should
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29 | be the ones which <emphasis>glibc was compiled against</emphasis>. These are
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30 | the headers which should remain accessible and so by copying them, we ensure
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31 | that we follow these guidelines. Also note that as long as you don't have
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32 | those symlinks, it is perfectly alright to have the kernel sources
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33 | in <filename>/usr/src/linux</filename>.</para>
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34 |
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35 | </sect2>
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