Try to use the new vfs rename flag RENAME_DT_WHT, to request from
underlying file system to mark whiteout directory entries as DT_WHT
instead of DT_CHR.
When whiteouts are classified as DT_WHT, ovl_dir_read_merged() can
distinguish between whiteouts to real character devices without
having to stat the suspect inodes.
Because this is only done for optimization, it is not a problem
if file system does not respect the new RENAME_DT_WHT flag, which
is most likely the case, so we retry the rename without the flag.
Even if DT_WHT type is set on rename using an experimental file
system patch, file system repair tools may later re-classify the
file type. That would break the optimization, but will not break
the functionality of ovl_dir_read_merged().
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/overlayfs/dir.c | 12 +++++++++---
fs/overlayfs/readdir.c | 2 +-
2 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 16e06dd..0e1c3f2 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -630,7 +630,13 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
struct dentry *upper;
struct dentry *opaquedir = NULL;
int err;
- int flags = 0;
+ /*
+ * Mark whiteout objects as DT_WHT instead of DT_CHR, so it easy
+ * to distinguish them real character devices in iterate_dir().
+ * File system repair tools may re-classify the file type
+ * and that will break optimization, but not functionality.
+ */
+ int flags = RENAME_DT_WHT;
if (WARN_ON(!workdir))
return -EROFS;
@@ -665,12 +671,12 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
goto out_dput_upper;
if (d_is_dir(upper))
- flags = RENAME_EXCHANGE;
+ flags |= RENAME_EXCHANGE;
err = ovl_do_rename(wdir, whiteout, udir, upper, flags);
if (err)
goto kill_whiteout;
- if (flags)
+ if (flags & RENAME_EXCHANGE)
ovl_cleanup(wdir, upper);
ovl_dentry_version_inc(dentry->d_parent);
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index f241b4e..32c5c96 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -98,7 +98,7 @@ static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
p->len = len;
p->type = d_type;
p->ino = ino;
- p->is_whiteout = false;
+ p->is_whiteout = (d_type == DT_WHT);
if (d_type == DT_CHR) {
p->next_maybe_whiteout = rdd->first_maybe_whiteout;
--
2.7.4
--
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