[lxc-devel] [PATCH 1/2 v2] Add clone_update_unexp_ovl_dir() function

[Serge Hallyn]

Quoting Christian Brauner (christianvanbrauner at gmail.com):
> On Oct 30, 2015 4:08 PM, "Serge Hallyn" <serge.hallyn at ubuntu.com> 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 | 103
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  src/lxc/confile.h |   3 ++
> > >  2 files changed, 106 insertions(+)
> > >
> > > diff --git a/src/lxc/confile.c b/src/lxc/confile.c
> > > index f7d6814..bc5b7ef 100644
> > > --- a/src/lxc/confile.c
> > > +++ b/src/lxc/confile.c
> > > @@ -2598,6 +2598,109 @@ void clear_unexp_config_line(struct lxc_conf
> *conf, const char *key, bool rm_sub
> > >       }
> > >  }
> > >
> > > +bool clone_update_unexp_ovl_dir(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)
> > > +                     return true;
> >
> > I think you should
> >
> >                 if (p >= lend)
> >                         continue;
> >
> > (and then you can skip the !*p check above as this should catch that)
> >
> > What you have will only get confused on invalid configs, but this would
> > be stricter and make me feel better.
> 
> Agreed. Than we should change that in the other function
> (clone_update_unexp_hooks()) as well.
> 
> >
> > > +             /* We check that when an lxc.mount.entry is found the
> substrings
> > > +              * " overlay " or " aufs " are present before we try to
> update
> > > +              * the line. This seems like a bit more safety. We can
> check for
> > > +              * " overlay " and " aufs " since both substrings need to
> have
> > > +              * at least one space before and after them. When the
> space
> > > +              * before or after is missing it is very likely that these
> > > +              * substrings are part of a path or something else. So we
> > > +              * shouldn't bother to do any further work...
> > > +              */
> > > +             if (!strstr(p, " overlay ") && !strstr(p, " aufs ")) {
> > > +                     lstart = lend;
> > > +                     continue;
> > > +             }
> >
> > But this will find " overlay " in any subsequent lines too right?  Don't
> you
> > need to limit your search to the line?  Maybe by saving *lend and setting
> > *lend = '\0'?
> 
> But we do want to check in all lines, don't we? If we do not find the
> substring in the current line we skip it and check the next one.

Right, so the you set *lend back to the saved *lend before going to the
top of the loop - there's someplace else i lxc that does this.