[lxc-devel] [PATCH] overlayfs: overlayfs.v22 or higher needs workdir option

[KATOH Yasufumi]

This patch creates workdir as "olwork", and retry mount with workdir
option when mount is failed.
It is used to prepare files before atomically swithing with
destination, and needs to be on the same filesystem as upperdir. It's
OK for it to be empty.

Signed-off-by: KATOH Yasufumi <karma at jazz.email.ne.jp>
---
 src/lxc/bdev.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 89 insertions(+), 7 deletions(-)

diff --git a/src/lxc/bdev.c b/src/lxc/bdev.c
index 8a819ab..ae5c77c 100644
--- a/src/lxc/bdev.c
+++ b/src/lxc/bdev.c
@@ -2154,10 +2154,12 @@ static int overlayfs_detect(const char *path)
 static int overlayfs_mount(struct bdev *bdev)
 {
 	char *options, *dup, *lower, *upper;
-	int len;
+	char *options_work, *work, *lastslash;
+	int lastslashidx;
+	int len, len2;
 	unsigned long mntflags;
 	char *mntdata;
-	int ret;
+	int ret, ret2;
 
 	if (strcmp(bdev->type, "overlayfs"))
 		return -22;
@@ -2175,6 +2177,19 @@ static int overlayfs_mount(struct bdev *bdev)
 	*upper = '\0';
 	upper++;
 
+	// overlayfs.v22 or higher needs workdir option
+	// if upper is /var/lib/lxc/c2/delta0,
+	// then workdir is /var/lib/lxc/c2/olwork
+	lastslash = strrchr(upper, '/');
+	if (!lastslash)
+		return -22;
+	lastslash++;
+	lastslashidx = lastslash - upper;
+
+	work = alloca(lastslashidx + 7);
+	strncpy(work, upper, lastslashidx+7);
+	strcpy(work+lastslashidx, "olwork");
+
 	if (parse_mntopts(bdev->mntopts, &mntflags, &mntdata) < 0) {
 		free(mntdata);
 		return -22;
@@ -2187,21 +2202,44 @@ static int overlayfs_mount(struct bdev *bdev)
 		len = strlen(lower) + strlen(upper) + strlen("upperdir=,lowerdir=,") + strlen(mntdata) + 1;
 		options = alloca(len);
 		ret = snprintf(options, len, "upperdir=%s,lowerdir=%s,%s", upper, lower, mntdata);
+
+		len2 = strlen(lower) + strlen(upper) + strlen(work)
+			+ strlen("upperdir=,lowerdir=,workdir=") + strlen(mntdata) + 1;
+		options_work = alloca(len2);
+		ret2 = snprintf(options, len2, "upperdir=%s,lowerdir=%s,workdir=%s,%s",
+				upper, lower, work, mntdata);
 	}
 	else {
 		len = strlen(lower) + strlen(upper) + strlen("upperdir=,lowerdir=") + 1;
 		options = alloca(len);
 		ret = snprintf(options, len, "upperdir=%s,lowerdir=%s", upper, lower);
+
+		len2 = strlen(lower) + strlen(upper) + strlen(work)
+			+ strlen("upperdir=,lowerdir=,workdir=") + 1;
+		options_work = alloca(len2);
+		ret2 = snprintf(options_work, len2, "upperdir=%s,lowerdir=%s,workdir=%s",
+			upper, lower, work);
 	}
-	if (ret < 0 || ret >= len) {
+	if (ret < 0 || ret >= len || ret2 < 0 || ret2 >= len2) {
 		free(mntdata);
 		return -1;
 	}
 
+	// mount without workdir option for overlayfs before v21
 	ret = mount(lower, bdev->dest, "overlayfs", MS_MGC_VAL | mntflags, options);
-	if (ret < 0)
-		SYSERROR("overlayfs: error mounting %s onto %s options %s",
+	if (ret < 0) {
+		INFO("overlayfs: error mounting %s onto %s options %s. retry with workdir",
 			lower, bdev->dest, options);
+
+		// retry with workdir option for overlayfs v22 and higher
+		ret = mount(lower, bdev->dest, "overlayfs", MS_MGC_VAL | mntflags, options_work);
+		if (ret < 0)
+			SYSERROR("overlayfs: error mounting %s onto %s options %s",
+				lower, bdev->dest, options_work);
+		else
+			INFO("overlayfs: mounted %s onto %s options %s",
+				lower, bdev->dest, options_work);
+	}
 	else
 		INFO("overlayfs: mounted %s onto %s options %s",
 			lower, bdev->dest, options);
@@ -2266,6 +2304,7 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
 
 	if (strcmp(orig->type, "dir") == 0) {
 		char *delta, *lastslash;
+		char *work;
 		int ret, len, lastslashidx;
 
 		// if we have /var/lib/lxc/c2/rootfs, then delta will be
@@ -2291,6 +2330,25 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
 		if (am_unpriv() && chown_mapped_root(delta, conf) < 0)
 			WARN("Failed to update ownership of %s", delta);
 
+		// make workdir for overlayfs.v22 or higher
+		// workdir is /var/lib/lxc/c2/olwork
+		// it is used to prepare files before atomically swithing with destination,
+		// and needs to be on the same filesystem as upperdir,
+		// so it's OK for it to be empty.
+		work = malloc(lastslashidx + 7);
+		if (!work)
+			return -1;
+		strncpy(work, new->dest, lastslashidx+1);
+		strcpy(work+lastslashidx, "olwork");
+		if (mkdir(work, 0755) < 0) {
+			SYSERROR("error: mkdir %s", work);
+			free(work);
+			return -1;
+		}
+		if (am_unpriv() && chown_mapped_root(work, conf) < 0)
+			WARN("Failed to update ownership of %s", work);
+		free(work);
+
 		// the src will be 'overlayfs:lowerdir:upperdir'
 		len = strlen(delta) + strlen(orig->src) + 12;
 		new->src = malloc(len);
@@ -2307,8 +2365,9 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
 		// I think we want to use the original lowerdir, with a
 		// private delta which is originally rsynced from the
 		// original delta
-		char *osrc, *odelta, *nsrc, *ndelta;
-		int len, ret;
+		char *osrc, *odelta, *nsrc, *ndelta, *work;
+		char *lastslash;
+		int len, ret, lastslashidx;
 		if (!(osrc = strdup(orig->src)))
 			return -22;
 		nsrc = index(osrc, ':') + 1;
@@ -2331,6 +2390,29 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
 		}
 		if (am_unpriv() && chown_mapped_root(ndelta, conf) < 0)
 			WARN("Failed to update ownership of %s", ndelta);
+
+		// make workdir for overlayfs.v22 or higher
+		// for details, see above.
+		lastslash = strrchr(ndelta, '/');
+		if (!lastslash)
+			return -1;
+		lastslash++;
+		lastslashidx = lastslash - ndelta;
+
+		work = malloc(lastslashidx + 7);
+		if (!work)
+			return -1;
+		strncpy(work, ndelta, lastslashidx+1);
+		strcpy(work+lastslashidx, "olwork");
+		if ((mkdir(work, 0755) < 0) && errno != EEXIST) {
+			SYSERROR("error: mkdir %s", work);
+			free(work);
+			return -1;
+		}
+		if (am_unpriv() && chown_mapped_root(work, conf) < 0)
+			WARN("Failed to update ownership of %s", work);
+		free(work);
+
 		struct rsync_data_char rdata;
 		rdata.src = odelta;
 		rdata.dest = ndelta;
-- 
2.1.1