Changeset 0058818

Timestamp:

10/01/2022 07:14:22 AM (19 months ago)

Author:

Xi Ruoyao <xry111@…>

Branches:

11.3, 11.3-rc1, 12.0, 12.0-rc1, 12.1, 12.1-rc1, bdubbs/gcc13, multilib, renodr/libudev-from-systemd, trunk, xry111/arm64, xry111/arm64-12.0, xry111/clfs-ng, xry111/loongarch, xry111/loongarch-12.0, xry111/loongarch-12.1, xry111/mips64el, xry111/pip3, xry111/rust-wip-20221008, xry111/update-glibc

Children:

2bf32ff

Parents:

a8f3814a

Message:

kernfs: modernize the explanation for bind mounting /dev

If you are using a "modern" distro (with devtmpfs and a modern udev
implementation), a bind mounting is actually not needed because you can
mount devtmpfs anyway. The only reason for bind mounting is to be
compatible with old host distros where /dev is a directory containing
many static device nodes, or is a tmpfs (not same as devtmpfs) popluated
by bootscript or an old udev (modern udev implementations, including
eudev and systemd-udev used by LFS, strictly requires a devtmpfs on
/dev).

So update the explanation to match the status quo.

Files:

• chapter07/kernfs.xml (modified) (1 diff)
• chapter09/udev.xml (modified) (1 diff)
• general.ent (modified) (1 diff)

chapter07/kernfs.xml

@@ -30 +30 @@
     <title>Mounting and Populating /dev</title>
 
-      <para>During a normal boot, the kernel automatically mounts the
-      <systemitem class="filesystem">devtmpfs</systemitem> filesystem on the
-      <filename class="directory">/dev</filename> directory; the
-      devices are created dynamically on that virtual filesystem when they
-      are first detected or accessed. Device creation is generally done during the
-      boot process by the kernel and the udev program.
-      Since the new system does not yet include udev and
-      has not yet been booted, it is necessary to mount and populate
-      the <filename class="directory">/dev</filename> directory manually. This is
-      accomplished by bind mounting the host system's
+      <para>During a normal boot of the LFS system, the kernel automatically
+      mounts the <systemitem class="filesystem">devtmpfs</systemitem>
+      filesystem on the
+      <filename class="directory">/dev</filename> directory; the kernel
+      creates device on that virtual filesystem during the boot process
+      or when a device is first detected or accessed. The udev daemon may
+      change the owner or permission of the device nodes created by the
+      kernel, or create new device nodes or symlinks to ease the work of
+      distro maintainers or system administrators.  (See
+      <xref linkend='ch-config-udev-device-node-creation'/> for details.)
+      If the host kernel supports &devtmpfs;, we can simply mount a
+      &devtmpfs; at <filename class='directory'>$LFS/dev</filename> and rely
+      on the kernel to populate it (the LFS building process does not need
+      the additional work onto &devtmpfs; by udev daemon).</para>
+
+      <para>But, some host kernels may lack &devtmpfs; support and these
+      host distros maintain the content of
+      <filename class="directory">/dev</filename> with different methods.
+      So the only host-agnostic way for populating
+      <filename class="directory">$LFS/dev</filename> is
+      bind mounting the host system's
       <filename class="directory">/dev</filename> directory. A bind mount is
       a special type of mount that allows you to create a mirror of a

chapter09/udev.xml

@@ -94 +94 @@
     </sect3>
 
-    <sect3>
+    <sect3 id='ch-config-udev-device-node-creation'>
       <title>Device Node Creation</title>
 

general.ent

@@ -122 +122 @@
 <!ENTITY root            "<systemitem class='username'>root</systemitem>">
 <!ENTITY lfs-user        "<systemitem class='username'>lfs</systemitem>">
+<!ENTITY devtmpfs        "<systemitem class='filesystem'>devtmpfs</systemitem>">
 <!ENTITY fstab           "<filename>/etc/fstab</filename>">
 <!ENTITY boot-dir        "<filename class='directory'>/boot</filename>">