[lxc-devel] [PATCH v3] Parse rootfs->path

[Serge Hallyn]

Quoting Christian Brauner (christianvanbrauner at gmail.com):
> On Tue, Oct 20, 2015 at 03:30:19PM +0000, Serge Hallyn wrote:
> > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > The mount_entry_overlay_dirs() and mount_entry_aufs_dirs() functions create
> > > workdirs and upperdirs for overlay and aufs lxc.mount.entry entries. They try
> > > to make sure that the workdirs and upperdirs can only be created under the
> > > containerdir (e.g. /path/to/the/container/CONTAINERNAME). In order to do this
> > > the right hand side of
> > > 
> > >                 if ((strncmp(upperdir, lxcpath, dirlen) == 0) && (strncmp(upperdir, rootfs->path, rootfslen) != 0))
> > > 
> > > was thought to check if the rootfs->path is not present in the workdir and
> > > upperdir mount options. But the current check is bogus since it will be
> > > trivially true whenever the container is a block-dev or overlay or aufs backed
> > > since the rootfs->path will then have a form like e.g.
> > > 
> > >         overlayfs:/some/path:/some/other/path
> > > 
> > > This patch adds the function ovl_get_rootfs_dir() which parses rootfs->path by
> > > searching backwards for the first occurrence of the delimiter pair ":/". We do
> > > not simply search for ":" since it might be used in path names. If ":/" is not
> > > found we assume the container is directory backed and simply return
> > > strdup(rootfs->path).
> > > 
> > > Signed-off-by: Christian Brauner <christianvanbrauner at gmail.com>
> > > ---
> > >  src/lxc/conf.c | 115 ++++++++++++++++++++++++++++++++++++++++++++-------------
> > >  1 file changed, 90 insertions(+), 25 deletions(-)
> > > 
> > > diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> > > index 16a62f8..301fe50 100644
> > > --- a/src/lxc/conf.c
> > > +++ b/src/lxc/conf.c
> > > @@ -1815,12 +1815,65 @@ static void cull_mntent_opt(struct mntent *mntent)
> > >  	}
> > >  }
> > >  
> > > +static char *ovl_get_rootfs_dir(const char *rootfs_path, size_t *rootfslen)
> > > +{
> > > +	char *end = NULL;
> > > +	char *s1 = NULL;
> > > +	char *s2 = NULL;
> > > +	char *rootfsdir = NULL;
> > > +	char *tmp = NULL;
> > > +	size_t len = 0;
> > > +	size_t slen = 0;
> > > +
> > > +	if (!rootfs_path || !rootfslen )
> > > +		return NULL;
> > > +
> > > +	*rootfslen = 0;
> > > +
> > > +	s1 = strdup(rootfs_path);
> > > +	if (!s1)
> > > +		return NULL;
> > > +
> > > +	s2 = malloc(strlen(rootfs_path) + 1);
> > > +	if (!s2) {
> > > +		free(s1);
> > > +		return NULL;
> > > +	}
> > > +	end = stpcpy(s2, rootfs_path);
> > > +
> > > +	/* If we find :/ in rootfs_path it means we either have a block-dev or
> > > +	 * overlay or aufs container. */
> > > +	while ((tmp = strrchr(s1, ':'))) {
> > > +		len = strlen(tmp);
> > > +		*rootfslen += len;
> > 
> > If it is "overlay:/some/rootfs:/some/delta0", you will find the
> > delta0 and return it as rootfsdir?
> > 
> > (or am i misreading?)
> Nope, I thought that in the case where the /some/rootfs refers to another
> containers rootfs it doesn't make sense to check against that path since this is
> covered by the left hand side of the check further down. But in the case of
> purely overlay-backed container it doesn't make sense... I'll rewrite that
> part. Are there any more special cases apart from aufs and overlay. We have
> 
> blockdev:/some/path
> 
> overlayfs:/some/path:/some/delta0
> aufs:/some/path:/some/delta0
> 
> Any more?

well bdev.c also looks for

loop:, lvm:, nbd:, and even dir:.  Not sure anyone uses these.

> > 
> > > +		if (strncmp(tmp, ":/", 2) == 0) {
> > > +			rootfsdir = strdup(end - *rootfslen + 1);
> > > +			break;
> > > +		} else {
> > > +			slen = strlen(s1);
> > > +			s1[slen - len] = '\0';
> > > +		}
> > > +	}
> > > +	free(s1);
> > > +
> > > +	if (!*rootfslen && !tmp)
> > > +		rootfsdir = s2;
> > > +	else
> > > +		free(s2);
> > > +
> > > +	if (rootfsdir)
> > > +		*rootfslen = strlen(rootfsdir);
> > > +
> > > +	return rootfsdir;
> > > +}
> > _______________________________________________
> > lxc-devel mailing list
> > lxc-devel at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-devel



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