overlayfs_clone: rsync the mounted rootfs

Closes #655

We can't rsync the delta as unpriv user because we can't create
the chardevs representing a whiteout.  We can however rsync the
rootfs and have the kernel create the whiteouts for us.

do_rsync: pass --delete

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

diff --git a/src/lxc/bdev.c b/src/lxc/bdev.c
index ada395880e4d1a53c62142185a29680de2f5e1ab..1694adbcb1f4203ab6fa0632e3ac68f24ede3ed9 100644 (file)
--- a/src/lxc/bdev.c
+++ b/src/lxc/bdev.c
@@ -72,6 +72,11 @@
 
 lxc_log_define(bdev, lxc);
 
+struct ovl_rsync_data {
+       struct bdev *orig;
+       struct bdev *new;
+};
+
 struct rsync_data_char {
        char *src;
        char *dest;
@@ -98,7 +103,7 @@ static int do_rsync(const char *src, const char *dest)
        s[l-2] = '/';
        s[l-1] = '\0';
 
-       execlp("rsync", "rsync", "-aHX", s, dest, (char *)NULL);
+       execlp("rsync", "rsync", "-aHX", "--delete", s, dest, (char *)NULL);
        exit(1);
 }
 
@@ -2328,6 +2333,68 @@ static int rsync_delta_wrapper(void *data)
        return rsync_delta(arg);
 }
 
+static int ovl_rsync(struct ovl_rsync_data *data)
+{
+       if (setgid(0) < 0) {
+               ERROR("Failed to setgid to 0");
+               return -1;
+       }
+       if (setgroups(0, NULL) < 0)
+               WARN("Failed to clear groups");
+       if (setuid(0) < 0) {
+               ERROR("Failed to setuid to 0");
+               return -1;
+       }
+
+       if (unshare(CLONE_NEWNS) < 0) {
+               SYSERROR("Unable to unshare mounts ns");
+               return -1;
+       }
+       if (detect_shared_rootfs()) {
+               if (mount(NULL, "/", NULL, MS_SLAVE|MS_REC, NULL)) {
+                       SYSERROR("Failed to make / rslave");
+                       ERROR("Continuing...");
+               }
+       }
+       if (overlayfs_mount(data->orig) < 0) {
+               ERROR("Failed mounting original container fs");
+               return -1;
+       }
+       if (overlayfs_mount(data->new) < 0) {
+               ERROR("Failed mounting new container fs");
+               return -1;
+       }
+       if (do_rsync(data->orig->dest, data->new->dest) < 0) {
+               ERROR("rsyncing %s to %s", data->orig->dest, data->new->dest);
+               return -1;
+       }
+
+       return 0;
+}
+
+static int ovl_rsync_wrapper(void *data)
+{
+       struct ovl_rsync_data *arg = data;
+       return ovl_rsync(arg);
+}
+
+static int ovl_do_rsync(struct bdev *orig, struct bdev *new, struct lxc_conf *conf)
+{
+       int ret = -1;
+       struct ovl_rsync_data rdata;
+
+       rdata.orig = orig;
+       rdata.new = new;
+       if (am_unpriv())
+               ret = userns_exec_1(conf, ovl_rsync_wrapper, &rdata);
+       else
+               ret = ovl_rsync(&rdata);
+       if (ret)
+               ERROR("copying overlayfs delta");
+
+       return ret;
+}
+
 static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char *oldname,
                const char *cname, const char *oldpath, const char *lxcpath, int snap,
                uint64_t newsize, struct lxc_conf *conf)
@@ -2460,19 +2527,6 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
                        WARN("Failed to update ownership of %s", work);
                free(work);
 
-               struct rsync_data_char rdata;
-               rdata.src = odelta;
-               rdata.dest = ndelta;
-               if (am_unpriv())
-                       ret = userns_exec_1(conf, rsync_delta_wrapper, &rdata);
-               else
-                       ret = rsync_delta(&rdata);
-               if (ret) {
-                       free(osrc);
-                       free(ndelta);
-                       ERROR("copying overlayfs delta");
-                       return -1;
-               }
                len = strlen(nsrc) + strlen(ndelta) + 12;
                new->src = malloc(len);
                if (!new->src) {
@@ -2485,6 +2539,8 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
                free(ndelta);
                if (ret < 0 || ret >= len)
                        return -ENOMEM;
+
+               return ovl_do_rsync(orig, new, conf);
        } else {
                ERROR("overlayfs clone of %s container is not yet supported",
                        orig->type);