[lxc-devel] [PATCH 1/2 v3] Add clone_update_unexp_ovl_paths() function

[Serge Hallyn]

Quoting Christian Brauner (christianvanbrauner at gmail.com):
> On Mon, Nov 02, 2015 at 02:38:16PM +0000, Serge Hallyn wrote:
> > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > This functions updates absolute paths for overlay upper- and workdirs so users
> > > can simply clone and start new containers without worrying about absolute paths
> > > in lxc.mount.entry overlay entries.
> > > 
> > > Signed-off-by: Christian Brauner <christianvanbrauner at gmail.com>
> > > ---
> > >  src/lxc/confile.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  src/lxc/confile.h |   3 ++
> > >  2 files changed, 105 insertions(+)
> > > 
> > > diff --git a/src/lxc/confile.c b/src/lxc/confile.c
> > > index f7d6814..47b0b8b 100644
> > > --- a/src/lxc/confile.c
> > > +++ b/src/lxc/confile.c
> > > @@ -2598,6 +2598,108 @@ void clear_unexp_config_line(struct lxc_conf *conf, const char *key, bool rm_sub
> > >  	}
> > >  }
> > >  
> > > +bool clone_update_unexp_ovl_paths(struct lxc_conf *conf, const char *oldpath,
> > > +				  const char *newpath, const char *oldname,
> > > +				  const char *newname, const char *ovldir)
> > > +{
> > > +	const char *key = "lxc.mount.entry";
> > > +	int ret;
> > > +	char *lstart = conf->unexpanded_config;
> > > +	char *lend;
> > > +	char *p;
> > > +	char *q;
> > > +	size_t newdirlen = strlen(ovldir) + strlen(newpath) + strlen(newname) + 2;
> > > +	size_t olddirlen = strlen(ovldir) + strlen(oldpath) + strlen(oldname) + 2;
> > > +	char *olddir = alloca(olddirlen + 1);
> > > +	char *newdir = alloca(newdirlen + 1);
> > > +
> > > +	ret = snprintf(olddir, olddirlen + 1, "%s=%s/%s", ovldir, oldpath, oldname);
> > > +	if (ret < 0 || ret >= olddirlen + 1) {
> > > +		ERROR("Bug in %s", __func__);
> > > +		return false;
> > > +	}
> > > +	ret = snprintf(newdir, newdirlen + 1, "%s=%s/%s", ovldir, newpath, newname);
> > > +	if (ret < 0 || ret >= newdirlen + 1) {
> > > +		ERROR("Bug in %s", __func__);
> > > +		return false;
> > > +	}
> > > +	if (!conf->unexpanded_config)
> > > +		return true;
> > > +	while (*lstart) {
> > > +		lend = strchr(lstart, '\n');
> > > +		if (!lend)
> > > +			lend = lstart + strlen(lstart);
> > > +		else
> > > +			lend++;
> > > +		if (strncmp(lstart, key, strlen(key)) != 0) {
> > > +			lstart = lend;
> > > +			continue;
> > > +		}
> > > +		p = strchr(lstart + strlen(key), '=');
> > > +		if (!p) {
> > > +			lstart = lend;
> > > +			continue;
> > > +		}
> > > +		p++;
> > > +		while (isblank(*p))
> > > +			p++;
> > > +		if (p >= lend)
> > > +                        continue;
> > > +                /* Whenever an lxc.mount.entry entry is found in a line we check
> > > +                *  if the substring " overlay" or the substring " aufs" is
> > > +                *  present before doing any further work. We check for "
> > > +                *  overlay" and " aufs" since both substrings need to have at
> > > +                *  least one space before them in a valid overlay
> > > +                *  lxc.mount.entry (/A B overlay).  When the space before is
> > > +                *  missing it is very likely that these substrings are part of a
> > > +                *  path or something else. */
> > > +		if (!strstr(p, " overlay") && !strstr(p, " aufs")) {
> > > +			lstart = lend;
> > > +			continue;
> > > +		}
> > > +		if (!(q = strstr(p, olddir))) {
> > > +			lstart = lend;
> > > +			continue;
> > > +		}
> > 
> > You're still not doing anything to ensure that 'overlays'/'aufs' and the
> > olddir are actually occurring on this same line.  So they could be showing
> > up in a comment or just later line.  Temporarily turning lend into '\0' is
> > the easiest way, but you could also do something like
> > 
> > 		if (!(q = strstr(p, " overlay")) && !(q=strstr(p, " aufs")))
> > 			goto next;
> > 		if (q >= lend)
> > 			goto next;
> > 
> > 		if (!(q = strstr(p, olddir)) || q >= lend)
> > 			goto next;
> > 
> > 		...
> > 
> > 		break;
> > next:
> > 		lstart = lend;
> > 		continue;
> 
> Wait, what I want is to find all lines:
> 
> lxc.mount.entry = /A B overlay upperdir=/B,workdir=/C
> 
> This also includes lines like:
> 
> # lxc.mount.entry = /A B overlay upperdir=/B,workdir=/C

Yes, but if i have 

lxc.mount.entry = /a B none bind,create=dir
# maybe i should use overlayfs?
# then i could mount it at upperdir=/B

You'll be treating that as one line.

> that are comments. If a comment is a valid lxc.mount.entry entry it seems
> updating it does not really matter. (That's also what clone_update_unexp_hooks()
> does for lxc.hook.* entries.)
> 
> I don't want to stop on the *first* match... I want to update all

I'm not saying to stop at the first match, hence 'goto next'.

> lxc.mount.entry entries. The way you do it seems like it stops as soon as it has
> found the *first* match. Is this what you want/expect from this function?