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system: clarify /dev management using devtmpfs + {mdev, eudev}

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The "Dynamic using mdev" and "Dynamic using eudev" /dev management
methods are using devtmpfs, just like "Dynamic using devtmpfs only",
on top of which they add either mdev or eudev. But their names might
suggest they use mdev only or eudev only.

Clarify their descriptions by adding "devtmpfs +" to make it
unambiguous.

[Thomas: rewrap the paragraphs in the manual. It makes the diff a lot
less readable, but we actually want the result to be wrapped.]

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
This commit is contained in:
Luca Ceresoli 2015-10-04 11:43:35 +02:00 committed by Thomas Petazzoni
parent 844f240185
commit 571552c468
2 changed files with 32 additions and 29 deletions
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57
docs/manual/configure.txt
View File

@ -295,39 +295,42 @@ different solutions to handle the +/dev+ directory :
responsibility to enable those two options (if you fail to do so,
your Buildroot system will not boot).
* The third solution is *Dynamic using mdev*. This method also relies
on the _devtmpfs_ virtual filesystem detailed above (so the
requirement to have +CONFIG_DEVTMPFS+ and +CONFIG_DEVTMPFS_MOUNT+
enabled in the kernel configuration still apply), but adds the
+mdev+ userspace utility on top of it. +mdev+ is a program part of
BusyBox that the kernel will call every time a device is added or
removed. Thanks to the +/etc/mdev.conf+ configuration file, +mdev+
can be configured to for example, set specific permissions or
ownership on a device file, call a script or application whenever a
device appears or disappear, etc. Basically, it allows _userspace_
to react on device addition and removal events. +mdev+ can for
example be used to automatically load kernel modules when devices
appear on the system. +mdev+ is also important if you have devices
that require a firmware, as it will be responsible for pushing the
firmware contents to the kernel. +mdev+ is a lightweight
implementation (with fewer features) of +udev+. For more details
about +mdev+ and the syntax of its configuration file, see
* The third solution is *Dynamic using devtmpfs + mdev*. This method
also relies on the _devtmpfs_ virtual filesystem detailed above (so
the requirement to have +CONFIG_DEVTMPFS+ and
+CONFIG_DEVTMPFS_MOUNT+ enabled in the kernel configuration still
apply), but adds the +mdev+ userspace utility on top of it. +mdev+
is a program part of BusyBox that the kernel will call every time a
device is added or removed. Thanks to the +/etc/mdev.conf+
configuration file, +mdev+ can be configured to for example, set
specific permissions or ownership on a device file, call a script
or application whenever a device appears or disappear,
etc. Basically, it allows _userspace_ to react on device addition
and removal events. +mdev+ can for example be used to automatically
load kernel modules when devices appear on the system. +mdev+ is
also important if you have devices that require a firmware, as it
will be responsible for pushing the firmware contents to the
kernel. +mdev+ is a lightweight implementation (with fewer
features) of +udev+. For more details about +mdev+ and the syntax
of its configuration file, see
http://git.busybox.net/busybox/tree/docs/mdev.txt.
* The fourth solution is *Dynamic using eudev*. This method also
relies on the _devtmpfs_ virtual filesystem detailed above, but
adds the +eudev+ userspace daemon on top of it. +eudev+ is a daemon
that runs in the background, and gets called by the kernel when a
device gets added or removed from the system. It is a more
heavyweight solution than +mdev+, but provides higher flexibility.
+eudev+ is a standalone version of +udev+, the original userspace
daemon used in most desktop Linux distributions, which is now part
of Systemd. For more details, see http://en.wikipedia.org/wiki/Udev.
* The fourth solution is *Dynamic using devtmpfs + eudev*. This
method also relies on the _devtmpfs_ virtual filesystem detailed
above, but adds the +eudev+ userspace daemon on top of it. +eudev+
is a daemon that runs in the background, and gets called by the
kernel when a device gets added or removed from the system. It is a
more heavyweight solution than +mdev+, but provides higher
flexibility. +eudev+ is a standalone version of +udev+, the
original userspace daemon used in most desktop Linux distributions,
which is now part of Systemd. For more details, see
http://en.wikipedia.org/wiki/Udev.
The Buildroot developers recommendation is to start with the *Dynamic
using devtmpfs only* solution, until you have the need for userspace
to be notified when devices are added/removed, or if firmwares are
needed, in which case *Dynamic using mdev* is usually a good solution.
needed, in which case *Dynamic using devtmpfs + mdev* is usually a
good solution.
Note that if +systemd+ is chosen as init system, /dev management will
be performed by the +udev+ program provided by +systemd+.

4
system/Config.in
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@ -110,11 +110,11 @@ config BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_DEVTMPFS
bool "Dynamic using devtmpfs only"
config BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV
bool "Dynamic using mdev"
bool "Dynamic using devtmpfs + mdev"
select BR2_PACKAGE_BUSYBOX
config BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV
bool "Dynamic using eudev"
bool "Dynamic using devtmpfs + eudev"
depends on BR2_USE_WCHAR
depends on !BR2_STATIC_LIBS
depends on BR2_USE_MMU # eudev