[PATCH v3 2/5] ovl: relax same fs constrain for constant st_ino

Amir Goldstein
2017-06-01T09:02:51Z

For the case of all layers not on the same fs, use the copy up
origin st_ino/st_dev for non-dir, if we know it.

This guarantied constant and persistent st_ino/st_dev for non-dir,
but not system-wide uniqueness, like in the same fs case.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
fs/overlayfs/inode.c | 32 +++++++++++++++++++-------------
1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index d613e2c41242..5f285c179bbd 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -65,6 +65,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
struct path realpath;
const struct cred *old_cred;
bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
+ bool samefs = ovl_same_sb(dentry->d_sb);
int err;

type = ovl_path_real(dentry, &realpath);
@@ -74,16 +75,16 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
goto out;

/*
- * When all layers are on the same fs, all real inode number are
- * unique, so we use the overlay st_dev, which is friendly to du -x.
- *
- * We also use st_ino of the copy up origin, if we know it.
- * This guaranties constant st_dev/st_ino across copy up.
+ * For non-dir or same fs, we use st_ino of the copy up origin, if we
+ * know it. This guaranties constant st_dev/st_ino across copy up.
*
* If filesystem supports NFS export ops, this also guaranties
* persistent st_ino across mount cycle.
+ *
+ * When all layers are on the same fs, all real inode number are
+ * unique, so we use the overlay st_dev, which is friendly to du -x.
*/
- if (ovl_same_sb(dentry->d_sb)) {
+ if (!is_dir || samefs) {
if (OVL_TYPE_ORIGIN(type)) {
struct kstat lowerstat;
u32 lowermask = STATX_INO | (!is_dir ? STATX_NLINK : 0);
@@ -94,7 +95,6 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
if (err)
goto out;

- WARN_ON_ONCE(stat->dev != lowerstat.dev);
/*
* Lower hardlinks are broken on copy up to different
* upper files, so we cannot use the lower origin st_ino
@@ -102,17 +102,23 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
*/
if (is_dir || lowerstat.nlink == 1)
stat->ino = lowerstat.ino;
+
+ if (samefs)
+ WARN_ON_ONCE(stat->dev != lowerstat.dev);
+ else
+ stat->dev = lowerstat.dev;
}
- stat->dev = dentry->d_sb->s_dev;
- } else if (is_dir) {
+ if (samefs)
+ stat->dev = dentry->d_sb->s_dev;
+ } else {
/*
- * If not all layers are on the same fs the pair {real st_ino;
- * overlay st_dev} is not unique, so use the non persistent
- * overlay st_ino.
- *
* Always use the overlay st_dev for directories, so 'find
* -xdev' will scan the entire overlay mount and won't cross the
* overlay mount boundaries.
+ *
+ * If not all layers are on the same fs the pair {real st_ino;
+ * overlay st_dev} is not unique, so use the non persistent
+ * overlay st_ino for directories.
*/
stat->dev = dentry->d_sb->s_dev;
stat->ino = dentry->d_inode->i_ino;
--
2.7.4