From: Luca Ceresoli <luca@lucaceresoli.net>
To: buildroot@busybox.net
Subject: [Buildroot] [RFC 3/6] system: add mdev-only /dev management (without devtmpfs)
Date: Mon, 14 Sep 2015 18:05:52 +0200 [thread overview]
Message-ID: <55F6F060.2060901@lucaceresoli.net> (raw)
In-Reply-To: <20150909132929.5c01433e@free-electrons.com>
Dear Thomas,
Thomas Petazzoni wrote:
> Luca,
>
> On Tue, 8 Sep 2015 23:28:51 +0200, Luca Ceresoli wrote:
>> There are a few reasons for an embedded Linux system not to use devtmpfs,
>> but still want to have dynamic /dev management. The most notable is to use
>> a kernel < 2.6.32, which have no devtmpfs support.
>>
>> For such corner cases, we introduce the ability to use busybox mdev for
>> /dev management even without devtmpfs.
>>
>> First, we need the BR2_ROOTFS_STATIC_DEVICE_TABLE just like the static
>> /dev management, in order to have the very basic devices such as /dev/null
>> and /dev/console until mdev is enabled.
>
> As said in another e-mail, this is not really true: we just need a very
> simple, two devices long, hard-coded device table. There is no need to
> allow the user to customize it. It would in fact be potentially
> misleading because the user who would add more devices in this static
> device table would not see them on the target: they would be
> "overridden" by the tmpfs mounted in /dev.
Yup, I did that in patch 4.
But now I removed that patch, and replaced with a different
implementation based on Arnout's suggestion of using BUSYBOX_DEVICES.
>
>> But doing this in S10mdev, which already does something similar, would be a
>> bit complex because when S10mdev runs /dev/shm and /dev/pts are already
>> mounted. We might unmount, recreate and mount them again, but devices in
>> them might be already in use. Or we could leave the "old" alone, and mount
>> them again in the newly created /dev. Both solutions are dirty and
>> potentially problematic.
>>
>> Instead we hook in inittab (both busybox and sysvinit) and do the same
>> incantations there, right after mounting /sys (needed for mdev) but before
>> any other actions on /dev, such as creating and mounting /dev/shm and
>> /dev/pts. We also skip installing S10mdev: it would do the same things
>> twice. In order to keep the inittab files concise and maintainable, this
>> taks is delegated to a helper script, /sbin/activate-mdev.
>
> taks -> task
Sure.
>
> One thing I dislike a bit is that there is quite a bit overlap between
> S10mdev and activate-mdev. As Arnout suggested, can you just mount a
> tmpfs in /dev in the inittab in the "mdev without devtmpfs" case, and
> then keep the normal S10mdev script?
v2 will do things this way.
>
>> diff --git a/package/busybox/busybox.mk b/package/busybox/busybox.mk
>> index 6e302f4..f95ff52 100644
>> --- a/package/busybox/busybox.mk
>> +++ b/package/busybox/busybox.mk
>> @@ -55,11 +55,18 @@ define BUSYBOX_PERMISSIONS
>> endef
>>
>> # If mdev will be used for device creation enable it and copy S10mdev to /etc/init.d
>> +ifeq ($(BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV)$(BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV_ONLY),y)
>> ifeq ($(BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV),y)
>> define BUSYBOX_INSTALL_MDEV_SCRIPT
>> $(INSTALL) -D -m 0755 package/busybox/S10mdev \
>> $(TARGET_DIR)/etc/init.d/S10mdev
>> endef
>> +else
>> +define BUSYBOX_INSTALL_MDEV_SCRIPT
>> + $(INSTALL) -D -m 0755 package/busybox/activate-mdev \
>> + $(TARGET_DIR)/sbin/activate-mdev
>> +endef
>> +endif
>
> Any reason to enclose the internal condition inside a bigger condition?
>
> (Of course, this becomes moot if we can use S10mdev in both cases)
Indeed, I removed entirely that script in the next iteration.
>
>> diff --git a/package/skeleton/skeleton.mk b/package/skeleton/skeleton.mk
>> index 48e7085..975e2a5 100644
>> --- a/package/skeleton/skeleton.mk
>> +++ b/package/skeleton/skeleton.mk
>> @@ -141,6 +141,7 @@ TARGET_FINALIZE_HOOKS += SKELETON_SYSTEM_GETTY
>> endif
>>
>> ifeq ($(BR2_INIT_BUSYBOX)$(BR2_INIT_SYSV),y)
>> +
>
> Not really related to the change.
I just wanted to highlight the two main blocks inside that ifeq:
[un]commenting read-write mount and [un]commenting the mdev line. The
code there is lengthy and not very readable IMHO. But ok, removed that.
>> diff --git a/system/Config.in b/system/Config.in
>> index 5bf5048..a10de1e 100644
>> --- a/system/Config.in
>> +++ b/system/Config.in
>> @@ -106,6 +106,10 @@ choice
>> config BR2_ROOTFS_DEVICE_CREATION_STATIC
>> bool "Static using device table"
>>
>> +config BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV_ONLY
>> + bool "Dynamic using mdev only"
>> + select BR2_PACKAGE_BUSYBOX
>> +
>> config BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_DEVTMPFS
>> bool "Dynamic using devtmpfs only"
>>
>> @@ -144,7 +148,7 @@ config BR2_ROOTFS_DEVICE_TABLE
>> config BR2_ROOTFS_STATIC_DEVICE_TABLE
>> string "Path to the device tables"
>> default "system/device_table_dev.txt"
>> - depends on BR2_ROOTFS_DEVICE_CREATION_STATIC
>> + depends on BR2_ROOTFS_DEVICE_CREATION_STATIC || BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV_ONLY
>
> As suggested above, we probably don't want to show this option in the
> BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV_ONLY case.
That's not present in v2.
--
Luca
next prev parent reply other threads:[~2015-09-14 16:05 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-08 21:28 [Buildroot] [RFC 0/6] mdev-only /dev management (without devtmpfs) Luca Ceresoli
2015-09-08 21:28 ` [Buildroot] [RFC 1/6] Move mounting /sys from fstab to inittab Luca Ceresoli
2015-09-09 9:12 ` Arnout Vandecappelle
2015-09-08 21:28 ` [Buildroot] [RFC 2/6] system: clarify /dev management using devtmpfs + {mdev, eudev} Luca Ceresoli
2015-09-09 9:40 ` Arnout Vandecappelle
2015-09-09 10:53 ` Luca Ceresoli
2015-09-09 10:54 ` Arnout Vandecappelle
2015-09-08 21:28 ` [Buildroot] [RFC 3/6] system: add mdev-only /dev management (without devtmpfs) Luca Ceresoli
2015-09-09 9:21 ` Arnout Vandecappelle
2015-09-09 12:29 ` Luca Ceresoli
2015-09-09 12:32 ` Arnout Vandecappelle
2015-09-09 13:54 ` Thomas Petazzoni
2015-09-14 13:47 ` Luca Ceresoli
2015-09-14 22:23 ` Arnout Vandecappelle
2015-09-15 22:35 ` Luca Ceresoli
2015-09-14 20:53 ` Peter Korsgaard
2015-09-14 21:34 ` Thomas Petazzoni
2015-09-14 21:38 ` Peter Korsgaard
2015-09-15 7:30 ` Thomas Petazzoni
2015-09-15 8:09 ` Peter Korsgaard
2015-09-15 9:41 ` Thomas Petazzoni
2015-09-15 12:01 ` Peter Korsgaard
2015-09-15 12:27 ` Arnout Vandecappelle
2015-09-15 12:32 ` Peter Korsgaard
2015-09-18 16:37 ` Luca Ceresoli
2015-09-15 13:03 ` Thomas Petazzoni
2015-09-15 13:14 ` Peter Korsgaard
2015-09-15 22:34 ` Luca Ceresoli
2015-10-01 9:36 ` Luca Ceresoli
2015-10-01 10:03 ` Peter Korsgaard
2015-09-15 22:31 ` Luca Ceresoli
2015-09-16 7:32 ` Peter Korsgaard
2015-09-18 15:47 ` Luca Ceresoli
2015-09-09 9:34 ` Arnout Vandecappelle
2015-09-09 11:23 ` Thomas Petazzoni
2015-09-09 11:29 ` Thomas Petazzoni
2015-09-09 20:33 ` Arnout Vandecappelle
2015-09-14 16:07 ` Luca Ceresoli
2015-09-14 16:05 ` Luca Ceresoli [this message]
2015-09-14 19:34 ` Thomas Petazzoni
2015-09-14 20:19 ` Arnout Vandecappelle
2015-09-15 22:07 ` Luca Ceresoli
2015-09-08 21:28 ` [Buildroot] [RFC 4/6] system: strip the initial /dev for mdev-only /dev management Luca Ceresoli
2015-09-08 21:28 ` [Buildroot] [RFC 5/6] docs/manual: document "Dynamic using mdev only" " Luca Ceresoli
2015-09-09 10:39 ` Arnout Vandecappelle
2015-09-08 21:28 ` [Buildroot] [RFC 6/6] **** DO NOT COMMIT THIS **** ugly stuff to test mdev-only " Luca Ceresoli
2015-09-09 9:26 ` [Buildroot] [RFC 0/6] mdev-only /dev management (without devtmpfs) Arnout Vandecappelle
2015-09-09 11:30 ` Thomas Petazzoni
2015-09-14 21:03 ` Peter Korsgaard
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