From d71297353dc45eaf8f7c252246490746708530f9 Mon Sep 17 00:00:00 2001 From: Maxime Ripard Date: Thu, 9 Oct 2014 15:07:35 +0200 Subject: [PATCH] libfstools/mount: Support latest overlayfs versions The latest overlayfs revisions (v23 and above) require an additional directory to be given in the options. Since we need to support both pre-v23 and post-v23 versions, take a lazy approach and try to first mount without a workdir, and if it fails, try with it. Signed-off-by: Maxime Ripard --- libfstools/mount.c | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) diff --git a/libfstools/mount.c b/libfstools/mount.c index efcfcd8..903043f 100644 --- a/libfstools/mount.c +++ b/libfstools/mount.c @@ -90,11 +90,35 @@ fopivot(char *rw_root, char *ro_root) } snprintf(overlay, sizeof(overlay), "overlayfs:%s", rw_root); - snprintf(lowerdir, sizeof(lowerdir), "lowerdir=/,upperdir=%s", rw_root); + /* + * First, try to mount without a workdir, for overlayfs v22 and before. + * If it fails, it means that we are probably using a v23 and + * later versions that require a workdir + */ + snprintf(lowerdir, sizeof(lowerdir), "lowerdir=/,upperdir=%s", rw_root); if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, lowerdir)) { - fprintf(stderr, "mount failed: %s\n", strerror(errno)); - return -1; + char upperdir[64], workdir[64]; + + snprintf(upperdir, sizeof(upperdir), "%s/upper", rw_root); + snprintf(workdir, sizeof(workdir), "%s/work", rw_root); + snprintf(lowerdir, sizeof(lowerdir), "lowerdir=/,upperdir=%s,workdir=%s", + upperdir, workdir); + + /* + * Overlay FS v23 and later requires both a upper and + * a work directory, both on the same filesystem, but + * not part of the same subtree. + * We can't really deal with these constraints without + * creating two new subdirectories in /overlay. + */ + mkdir(upperdir, 0755); + mkdir(workdir, 0755); + + if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, lowerdir)) { + fprintf(stderr, "mount failed: %s, options %s\n", strerror(errno), lowerdir); + return -1; + } } return pivot("/mnt", ro_root); -- 2.25.1