[Buildroot] [PATCH 1/1] package/systemd: pre-create directories for services

[Buildroot] [PATCH 1/1] package/systemd: pre-create directories for services

[Norbert Lange]

this adds a new hook and a corresponding variable to add
addirectories and files after installation.

various services need directories in /var when they are started,
and create them if necessary. Creating those before, allows
those services to start even if /var is read-only.

Signed-off-by: Norbert Lange <nolange79@gmail.com>
---
 package/systemd/systemd.mk | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/package/systemd/systemd.mk b/package/systemd/systemd.mk
index c202f5be02..b57365872e 100644
--- a/package/systemd/systemd.mk
+++ b/package/systemd/systemd.mk
@@ -317,6 +317,7 @@ endif
 
 ifeq ($(BR2_PACKAGE_SYSTEMD_LOGIND),y)
 SYSTEMD_CONF_OPTS += -Dlogind=true
+SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/linger/
 else
 SYSTEMD_CONF_OPTS += -Dlogind=false
 endif
@@ -336,6 +337,7 @@ endif
 ifeq ($(BR2_PACKAGE_SYSTEMD_HOMED),y)
 SYSTEMD_CONF_OPTS += -Dhomed=true
 SYSTEMD_DEPENDENCIES += cryptsetup openssl
+SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/home/
 else
 SYSTEMD_CONF_OPTS += -Dhomed=false
 endif
@@ -380,12 +382,14 @@ endif
 ifeq ($(BR2_PACKAGE_SYSTEMD_COREDUMP),y)
 SYSTEMD_CONF_OPTS += -Dcoredump=true
 SYSTEMD_COREDUMP_USER = systemd-coredump -1 systemd-coredump -1 * - - - systemd core dump processing
+SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/coredump/
 else
 SYSTEMD_CONF_OPTS += -Dcoredump=false
 endif
 
 ifeq ($(BR2_PACKAGE_SYSTEMD_PSTORE),y)
 SYSTEMD_CONF_OPTS += -Dpstore=true
+SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/pstore/
 else
 SYSTEMD_CONF_OPTS += -Dpstore=false
 endif
@@ -436,6 +440,7 @@ endif
 ifeq ($(BR2_PACKAGE_SYSTEMD_TIMESYNCD),y)
 SYSTEMD_CONF_OPTS += -Dtimesyncd=true
 SYSTEMD_TIMESYNCD_USER = systemd-timesync -1 systemd-timesync -1 * - - - systemd Time Synchronization
+SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/timesync/
 else
 SYSTEMD_CONF_OPTS += -Dtimesyncd=false
 endif
@@ -485,18 +490,23 @@ ifneq ($(SYSTEMD_FALLBACK_HOSTNAME),)
 SYSTEMD_CONF_OPTS += -Dfallback-hostname=$(SYSTEMD_FALLBACK_HOSTNAME)
 endif
 
+define SYSTEMD_INSTALL_ENTRY_HOOK
+	mkdir -p -m700 $(TARGET_DIR)/var/lib/private $(TARGET_DIR)/var/log/private \
+		$(TARGET_DIR)/var/cache/private
+	mkdir -p -m1777 $(TARGET_DIR)/var/tmp
+	$(if $(BR2_PACKAGE_SYSTEMD_MACHINED),mkdir -p -m700 $(TARGET_DIR)/var/lib/machines)
+	mkdir -p $(addprefix $(TARGET_DIR)/,var/lib $(filter %/,$(SYSTEMD_POST_INSTALL_ENTRIES)))
+	touch $(addprefix $(TARGET_DIR)/,etc/machine-id $(filter-out %/,$(SYSTEMD_POST_INSTALL_ENTRIES)))
+endef
+
 define SYSTEMD_INSTALL_INIT_HOOK
 	ln -fs multi-user.target \
 		$(TARGET_DIR)/usr/lib/systemd/system/default.target
 endef
 
-define SYSTEMD_INSTALL_MACHINEID_HOOK
-	touch $(TARGET_DIR)/etc/machine-id
-endef
-
 SYSTEMD_POST_INSTALL_TARGET_HOOKS += \
+	SYSTEMD_INSTALL_ENTRY_HOOK \
 	SYSTEMD_INSTALL_INIT_HOOK \
-	SYSTEMD_INSTALL_MACHINEID_HOOK \
 	SYSTEMD_INSTALL_RESOLVCONF_HOOK
 
 define SYSTEMD_INSTALL_IMAGES_CMDS
@@ -532,6 +542,10 @@ endef
 
 SYSTEMD_TARGET_FINALIZE_HOOKS += SYSTEMD_INSTALL_NSSCONFIG_HOOK
 
+define SYSTEMD_PERMISSIONS
+	$(if $(SYSTEMD_TIMESYNCD_USER),/var/lib/systemd/timesync d 755 systemd-timesync systemd-timesync - - - - -)
+endef
+
 ifneq ($(call qstrip,$(BR2_TARGET_GENERIC_GETTY_PORT)),)
 # systemd provides multiple units to autospawn getty as neede
 # * getty at .service to start a getty on normal TTY
-- 
2.27.0

[Buildroot] [PATCH 1/1] package/systemd: pre-create directories for services

[Yann E. MORIN]

Norbert, All,

On 2020-07-18 01:42 +0200, Norbert Lange spake thusly:
> this adds a new hook and a corresponding variable to add
> addirectories and files after installation.
> 
> various services need directories in /var when they are started,
> and create them if necessary. Creating those before, allows
> those services to start even if /var is read-only.
> 
> Signed-off-by: Norbert Lange <nolange79@gmail.com>
> ---
>  package/systemd/systemd.mk | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/package/systemd/systemd.mk b/package/systemd/systemd.mk
> index c202f5be02..b57365872e 100644
> --- a/package/systemd/systemd.mk
> +++ b/package/systemd/systemd.mk
> @@ -317,6 +317,7 @@ endif
>  
>  ifeq ($(BR2_PACKAGE_SYSTEMD_LOGIND),y)
>  SYSTEMD_CONF_OPTS += -Dlogind=true
> +SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/linger/

The naming is not nice. Also, paths should be absolute:

    SYSTEMD_CREATE_DIRS += /var/lib/systemd/linger/

However, I am not fond of mixing the directories creation with two
infras: post-isntall hooks and _PERMISSIONS tables.

So, in fact:

    SYSTEMD_LOGIND_PERMISIONS = /var/lib/systemd/linger d 755 0 0 - - - - -

Ditto for the others conditional directories. And of course, we should
also treat the non-conditional ones similarly.

[--SNIP--]
> @@ -436,6 +440,7 @@ endif
>  ifeq ($(BR2_PACKAGE_SYSTEMD_TIMESYNCD),y)
>  SYSTEMD_CONF_OPTS += -Dtimesyncd=true
>  SYSTEMD_TIMESYNCD_USER = systemd-timesync -1 systemd-timesync -1 * - - - systemd Time Synchronization
> +SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/timesync/

    SYSTEMD_TIMESYNCD_PERMISIONS = /var/lib/systemd/timesync d 755 systemd-timesync systemd-timesync - - - - -

[--SNIP--]
> @@ -485,18 +490,23 @@ ifneq ($(SYSTEMD_FALLBACK_HOSTNAME),)
>  SYSTEMD_CONF_OPTS += -Dfallback-hostname=$(SYSTEMD_FALLBACK_HOSTNAME)
>  endif
>  
> +define SYSTEMD_INSTALL_ENTRY_HOOK
> +	mkdir -p -m700 $(TARGET_DIR)/var/lib/private $(TARGET_DIR)/var/log/private \
> +		$(TARGET_DIR)/var/cache/private
> +	mkdir -p -m1777 $(TARGET_DIR)/var/tmp
> +	$(if $(BR2_PACKAGE_SYSTEMD_MACHINED),mkdir -p -m700 $(TARGET_DIR)/var/lib/machines)
> +	mkdir -p $(addprefix $(TARGET_DIR)/,var/lib $(filter %/,$(SYSTEMD_POST_INSTALL_ENTRIES)))
> +	touch $(addprefix $(TARGET_DIR)/,etc/machine-id $(filter-out %/,$(SYSTEMD_POST_INSTALL_ENTRIES)))
> +endef

This would thus no longer be needed.

>  define SYSTEMD_INSTALL_INIT_HOOK
>  	ln -fs multi-user.target \
>  		$(TARGET_DIR)/usr/lib/systemd/system/default.target
>  endef
>  
> -define SYSTEMD_INSTALL_MACHINEID_HOOK
> -	touch $(TARGET_DIR)/etc/machine-id
> -endef

This could also probably be replaced with a non-conditional entry in the
permissions table, see below...

>  SYSTEMD_POST_INSTALL_TARGET_HOOKS += \
> +	SYSTEMD_INSTALL_ENTRY_HOOK \
>  	SYSTEMD_INSTALL_INIT_HOOK \
> -	SYSTEMD_INSTALL_MACHINEID_HOOK \
>  	SYSTEMD_INSTALL_RESOLVCONF_HOOK
>  
>  define SYSTEMD_INSTALL_IMAGES_CMDS
> @@ -532,6 +542,10 @@ endef
>  
>  SYSTEMD_TARGET_FINALIZE_HOOKS += SYSTEMD_INSTALL_NSSCONFIG_HOOK
>  
> +define SYSTEMD_PERMISSIONS
> +	$(if $(SYSTEMD_TIMESYNCD_USER),/var/lib/systemd/timesync d 755 systemd-timesync systemd-timesync - - - - -)
> +endef

We usually do not use conditional in the permissions tables, but define
conditional variables that we then re-use (see above):

    define SYSTEMD_PERMISSIONS
        /etc/machine-id f 644 0 0 - - - - -
        $(SYSTEMD_LOGIND_PERMISIONS)
        $(SYSTEMD_TIMESYNCD_PERMISIONS)
        ...
    endef

Regards,
Yann E. MORIN.

> +
>  ifneq ($(call qstrip,$(BR2_TARGET_GENERIC_GETTY_PORT)),)
>  # systemd provides multiple units to autospawn getty as neede
>  # * getty at .service to start a getty on normal TTY
> -- 
> 2.27.0
> 

-- 
.-----------------.--------------------.------------------.--------------------.
|  Yann E. MORIN  | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___               |
| +33 561 099 427 `------------.-------:  X  AGAINST      |  \e/  There is no  |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL    |   v   conspiracy.  |
'------------------------------^-------^------------------^--------------------'

[Buildroot] [PATCH 1/1] package/systemd: pre-create directories for services

[Jérémy ROSEN]

I am kinda philosophically torn on this one...


According to man:file-hierarchy, /var MUST be writable (it MAY be a tmpfs
if the system has no persistent, writable storage)

This means that daemons can assume that /var will be writable, and we might
be starting a wild goose hunt to get them
working in all cases.
The clean way to have a file go in /var (at least with systemd) is to put
it in /usr/share/factory/var/ and systemd will copy it to
/var on first boot (or every boot if it's a tmpfs)

this has the added advantage that /var can be empty at install time, can be
easily reset by reformatting/emptying
without breaking the system.

I have no idea how factory is handled in sysV.

If buildroot wants to support read-only /var, it's supporting a "buggy
setup" according to various standards including FHS.
And yeah... it's a buggy setup, but it's also a common setup :(

So, I guess it's important to point that out but I don't really know what
the correct answer is for buildroot..

Jeremy


Le sam. 18 juil. 2020 ? 23:16, Yann E. MORIN <yann.morin.1998@free.fr> a
?crit :

> Norbert, All,
>
> On 2020-07-18 01:42 +0200, Norbert Lange spake thusly:
> > this adds a new hook and a corresponding variable to add
> > addirectories and files after installation.
> >
> > various services need directories in /var when they are started,
> > and create them if necessary. Creating those before, allows
> > those services to start even if /var is read-only.
> >
> > Signed-off-by: Norbert Lange <nolange79@gmail.com>
> > ---
> >  package/systemd/systemd.mk | 24 +++++++++++++++++++-----
> >  1 file changed, 19 insertions(+), 5 deletions(-)
> >
> > diff --git a/package/systemd/systemd.mk b/package/systemd/systemd.mk
> > index c202f5be02..b57365872e 100644
> > --- a/package/systemd/systemd.mk
> > +++ b/package/systemd/systemd.mk
> > @@ -317,6 +317,7 @@ endif
> >
> >  ifeq ($(BR2_PACKAGE_SYSTEMD_LOGIND),y)
> >  SYSTEMD_CONF_OPTS += -Dlogind=true
> > +SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/linger/
>
> The naming is not nice. Also, paths should be absolute:
>
>     SYSTEMD_CREATE_DIRS += /var/lib/systemd/linger/
>
> However, I am not fond of mixing the directories creation with two
> infras: post-isntall hooks and _PERMISSIONS tables.
>
> So, in fact:
>
>     SYSTEMD_LOGIND_PERMISIONS = /var/lib/systemd/linger d 755 0 0 - - - - -
>
> Ditto for the others conditional directories. And of course, we should
> also treat the non-conditional ones similarly.
>
> [--SNIP--]
> > @@ -436,6 +440,7 @@ endif
> >  ifeq ($(BR2_PACKAGE_SYSTEMD_TIMESYNCD),y)
> >  SYSTEMD_CONF_OPTS += -Dtimesyncd=true
> >  SYSTEMD_TIMESYNCD_USER = systemd-timesync -1 systemd-timesync -1 * - -
> - systemd Time Synchronization
> > +SYSTEMD_POST_INSTALL_ENTRIES += var/lib/systemd/timesync/
>
>     SYSTEMD_TIMESYNCD_PERMISIONS = /var/lib/systemd/timesync d 755
> systemd-timesync systemd-timesync - - - - -
>
> [--SNIP--]
> > @@ -485,18 +490,23 @@ ifneq ($(SYSTEMD_FALLBACK_HOSTNAME),)
> >  SYSTEMD_CONF_OPTS += -Dfallback-hostname=$(SYSTEMD_FALLBACK_HOSTNAME)
> >  endif
> >
> > +define SYSTEMD_INSTALL_ENTRY_HOOK
> > +     mkdir -p -m700 $(TARGET_DIR)/var/lib/private
> $(TARGET_DIR)/var/log/private \
> > +             $(TARGET_DIR)/var/cache/private
> > +     mkdir -p -m1777 $(TARGET_DIR)/var/tmp
> > +     $(if $(BR2_PACKAGE_SYSTEMD_MACHINED),mkdir -p -m700
> $(TARGET_DIR)/var/lib/machines)
> > +     mkdir -p $(addprefix $(TARGET_DIR)/,var/lib $(filter
> %/,$(SYSTEMD_POST_INSTALL_ENTRIES)))
> > +     touch $(addprefix $(TARGET_DIR)/,etc/machine-id $(filter-out
> %/,$(SYSTEMD_POST_INSTALL_ENTRIES)))
> > +endef
>
> This would thus no longer be needed.
>
> >  define SYSTEMD_INSTALL_INIT_HOOK
> >       ln -fs multi-user.target \
> >               $(TARGET_DIR)/usr/lib/systemd/system/default.target
> >  endef
> >
> > -define SYSTEMD_INSTALL_MACHINEID_HOOK
> > -     touch $(TARGET_DIR)/etc/machine-id
> > -endef
>
> This could also probably be replaced with a non-conditional entry in the
> permissions table, see below...
>
> >  SYSTEMD_POST_INSTALL_TARGET_HOOKS += \
> > +     SYSTEMD_INSTALL_ENTRY_HOOK \
> >       SYSTEMD_INSTALL_INIT_HOOK \
> > -     SYSTEMD_INSTALL_MACHINEID_HOOK \
> >       SYSTEMD_INSTALL_RESOLVCONF_HOOK
> >
> >  define SYSTEMD_INSTALL_IMAGES_CMDS
> > @@ -532,6 +542,10 @@ endef
> >
> >  SYSTEMD_TARGET_FINALIZE_HOOKS += SYSTEMD_INSTALL_NSSCONFIG_HOOK
> >
> > +define SYSTEMD_PERMISSIONS
> > +     $(if $(SYSTEMD_TIMESYNCD_USER),/var/lib/systemd/timesync d 755
> systemd-timesync systemd-timesync - - - - -)
> > +endef
>
> We usually do not use conditional in the permissions tables, but define
> conditional variables that we then re-use (see above):
>
>     define SYSTEMD_PERMISSIONS
>         /etc/machine-id f 644 0 0 - - - - -
>         $(SYSTEMD_LOGIND_PERMISIONS)
>         $(SYSTEMD_TIMESYNCD_PERMISIONS)
>         ...
>     endef
>
> Regards,
> Yann E. MORIN.
>
> > +
> >  ifneq ($(call qstrip,$(BR2_TARGET_GENERIC_GETTY_PORT)),)
> >  # systemd provides multiple units to autospawn getty as neede
> >  # * getty at .service to start a getty on normal TTY
> > --
> > 2.27.0
> >
>
> --
>
> .-----------------.--------------------.------------------.--------------------.
> |  Yann E. MORIN  | Real-Time Embedded | /"\ ASCII RIBBON | Erics'
> conspiracy: |
> | +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___
>      |
> | +33 561 099 427 `------------.-------:  X  AGAINST      |  \e/  There is
> no  |
> | http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL    |   v
>  conspiracy.  |
>
> '------------------------------^-------^------------------^--------------------'
>


-- 
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*J?r?my ROSEN*
Architecte technique

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[Buildroot] [PATCH 1/1] package/systemd: pre-create directories for services

[Norbert Lange]

Am Mo., 20. Juli 2020 um 10:42 Uhr schrieb J?r?my ROSEN <
jeremy.rosen@smile.fr>:

> I am kinda philosophically torn on this one...
>
>
> According to man:file-hierarchy, /var MUST be writable (it MAY be a tmpfs
> if the system has no persistent, writable storage)
>

I'd not confuse the "distribution image" (the thing that buildroot creates)
with the running system.

To me, buildroot should do *everything that's possible* up-front.


> This means that daemons can assume that /var will be writable, and we
> might be starting a wild goose hunt to get them
> working in all cases.
>

Nope, definitely not the aim for buildroot. Personally I would aim at some
sort of base system still being accessible, even if /var is read-only
(might happen if the block-device has errors).
systemd actively tries to do this, v246 will have some fallbacks do
services can start if /var/tmp is read-only (albeit in obviously reduced
fashion).

The clean way to have a file go in /var (at least with systemd) is to put
> it in /usr/share/factory/var/ and systemd will copy it to
> /var on first boot (or every boot if it's a tmpfs)
>

No, no, no. the factory approach is one of the most fragile I have ever
seen., See [1] for a short list of issues,
[2] for a patch with conflicting use.
That's something requiring a "wild goose hunt" to get in shape.

A clean approach is to mount a overlayfs, ideally already in the initramfs,
or to separate /usr into a RO image. Both approaches are hindered with the
intransparent
logic hidden behind the innocent REMOUNT_ROOTFS_RW option.

The best in-image option would be to either:
- hook /sbin/init
- create a systemd-unit that is run after /var is mounted and before
tmpfilesd-create is run.

At one of these points, do either an overlayfs or copying over the contents
to a new tmpfs, then bindmounting it to /var.

I'd still do this as a separate option to REMOUNT_ROOTFS_RW, perhaps even
as its own package.

this has the added advantage that /var can be empty at install time, can be
> easily reset by reformatting/emptying
> without breaking the system.
>

Thats what tmpfilesd is for, ideally it doesn't require copying over the
old contents. Then it works with an empty /var whether you use the rw or ro
option in buildroot,
you just might need to add a tmpfs mount there.

I have no idea how factory is handled in sysV.
>
> If buildroot wants to support read-only /var, it's supporting a "buggy
> setup" according to various standards including FHS.
> And yeah... it's a buggy setup, but it's also a common setup :(
>

I'd call it a robust setup, if things still work in a reduced fashion.
But again I use buildroot as a "distribution image" generator, I do mount
an overlayfs over the whole fs in the initramfs,
something that seems official support as you cant mount a .tar file.


>
> So, I guess it's important to point that out but I don't really know what
> the correct answer is for buildroot..
>

For this patch, its just a question if the work (as in maintainance cost)
is acceptable to pre-create the directories,
I don't see any downsides, philosophically or pragmatically.

How RO-systems should be supported is another question, but in my
opionion a bind-mount script that works
on all init-systems (just maybe hooked-in differently) and doesnt causes a
host of side-effects would be alot better than the status quo.

I'll append a small example, how such a bind-mount script (with overlay)
would look like.

[1] - http://lists.busybox.net/pipermail/buildroot/2020-July/287016.html
[2] - http://lists.busybox.net/pipermail/buildroot/2020-July/287200.html

ROOTFSDIR=/tmp/rootfs
OVLDIR=/run/ovl

# create a separate filesystem for testing
mkdir $ROOTFSDIR
mount -t tmpfs tmpfs_root_to $ROOTFSDIR
mkdir $ROOTFSDIR/var
touch $ROOTFSDIR/var/upperfile
mount -o remount,ro $ROOTFSDIR

# real overlay script

mkdir $OVLDIR
mount -t tmpfs tmpfs_root_ovl $OVLDIR
mkdir $OVLDIR/lower $OVLDIR/upper $OVLDIR/work

mount --bind $ROOTFSDIR/var $OVLDIR/lower
mount -t overlay -o
lowerdir=$OVLDIR/lower,upperdir=$OVLDIR/upper,workdir=$OVLDIR/work
overlay_var $ROOTFSDIR/var
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