overlay: fix race condition when switching to jffs2

There is a race between `cp -a /tmp/root/* /rom/overlay` from
libfstools/overlay.c and a process creating new file(s) before
pivot(/rom, /mnt) occured.
That is a process can create a file and it will not be copied.

To workaround this, do additional copy after jffs2 is ready.
This doesn't completely solve the problem but since there
was no other fix provided since original RFC [1], it is better
than nothiing.

[1] https://www.mail-archive.com/openwrt-devel@lists.openwrt.org/msg38218.html

Signed-off-by: Roman Yeryomin <roman@advem.lv>

diff --git a/libfstools/overlay.c b/libfstools/overlay.c
index 7ada5ffc3b37c1c370f945a55cceef6b2efe0a92..8423a57c36df8fd67b445c3ff76ecc9b2afd8db6 100644 (file)
--- a/libfstools/overlay.c
+++ b/libfstools/overlay.c
@@ -243,6 +243,10 @@ jffs2_switch(struct volume *v)
                ULOG_INFO("performing overlay whiteout\n");
                umount2("/tmp/root", MNT_DETACH);
                foreachdir("/overlay/", handle_whiteout);
+
+               /* try hard to be in sync */
+               ULOG_INFO("syncronizing overlay\n");
+               system("cp -a /tmp/root/upper/* / 2>/dev/null");
                break;
 
        case FS_EXT4: