netdev - Re: [PATCH iproute2-next v2] arpd: create /var/lib/arpd on first use

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Message-ID: <Zff9ReznTN4h-Jrh@framework>
Date: Mon, 18 Mar 2024 09:37:25 +0100
From: Max Gautier <mg@....gautier.name>
To: Ratheesh Kannoth <rkannoth@...vell.com>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH iproute2-next v2] arpd: create /var/lib/arpd on first use

On Mon, Mar 18, 2024 at 08:26:13AM +0530, Ratheesh Kannoth wrote:
> On 2024-03-17 at 14:31:24, Max Gautier (mg@....gautier.name) wrote:
> > The motivation is to build distributions packages without /var to go
> > towards stateless systems, see link below (TL;DR: provisionning anything
> > outside of /usr on boot).
> >
> > We only try do create the database directory when it's in the default
> > location, and assume its parent (/var/lib in the usual case) exists.
> >
> > Links: https://0pointer.net/blog/projects/stateless.html
> > Signed-off-by: Max Gautier <mg@....gautier.name>
> > ---
> >  Makefile    |  2 +-
> >  misc/arpd.c | 12 +++++++++++-
> >  2 files changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 8024d45e..2b2c3dec 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -42,6 +42,7 @@ DEFINES+=-DCONF_USR_DIR=\"$(CONF_USR_DIR)\" \
> >           -DCONF_ETC_DIR=\"$(CONF_ETC_DIR)\" \
> >           -DNETNS_RUN_DIR=\"$(NETNS_RUN_DIR)\" \
> >           -DNETNS_ETC_DIR=\"$(NETNS_ETC_DIR)\" \
> > +         -DARPDDIR=\"$(ARPDDIR)\" \
> >           -DCONF_COLOR=$(CONF_COLOR)
> >
> >  #options for AX.25
> > @@ -104,7 +105,6 @@ config.mk:
> >  install: all
> >  	install -m 0755 -d $(DESTDIR)$(SBINDIR)
> >  	install -m 0755 -d $(DESTDIR)$(CONF_USR_DIR)
> > -	install -m 0755 -d $(DESTDIR)$(ARPDDIR)
> >  	install -m 0755 -d $(DESTDIR)$(HDRDIR)
> >  	@for i in $(SUBDIRS);  do $(MAKE) -C $$i install; done
> >  	install -m 0644 $(shell find etc/iproute2 -maxdepth 1 -type f) $(DESTDIR)$(CONF_USR_DIR)
> > diff --git a/misc/arpd.c b/misc/arpd.c
> > index 1ef837c6..a64888aa 100644
> > --- a/misc/arpd.c
> > +++ b/misc/arpd.c
> > @@ -19,6 +19,7 @@
> >  #include <fcntl.h>
> >  #include <sys/uio.h>
> >  #include <sys/socket.h>
> > +#include <sys/stat.h>
> >  #include <sys/time.h>
> >  #include <time.h>
> >  #include <signal.h>
> > @@ -35,7 +36,8 @@
> >  #include "rt_names.h"
> >
> >  DB	*dbase;
> > -char	*dbname = "/var/lib/arpd/arpd.db";
> > +char const	default_dbname[] = ARPDDIR "/arpd.db";
> > +char const	*dbname = default_dbname;
> >
> >  int	ifnum;
> >  int	*ifvec;
> > @@ -668,6 +670,14 @@ int main(int argc, char **argv)
> >  		}
> >  	}
> >
> > +	if (strcmp(default_dbname, dbname) == 0
> > +			&& mkdir(ARPDDIR, 0755) != 0
> > +			&& errno != EEXIST
> why do you need errno != EEXIST case ? mkdir() will return error in this case as well.

EEXIST is not an error in this case: if the default location already
exist, all is good. mkdir would still return -1 in this case, so we need
to exclude it manually.

> > +			) {
> > +		perror("create_db_dir");
> > +		exit(-1);
> > +	}
> > +
> >  	dbase = dbopen(dbname, O_CREAT|O_RDWR, 0644, DB_HASH, NULL);
> >  	if (dbase == NULL) {
> >  		perror("db_open");
> > --
> > 2.44.0
> >

-- 
Max Gautier