On lookup of non directory, we try to decode the origin file handle
stored in upper inode. The origin file handle is supposed to be decoded
to a disconnected non-dir dentry, which is fine, because we only need
the lower inode of a copy up origin.
However, if the origin file handle somehow turns out to be a directory
we pay the expensive cost of reconnecting the directory dentry, only to
get a mismatch file type and drop the dentry.
Optimize this case by explicitly opting out of reconnecting the dentry.
Opting-out of reconnect is done by passing a NULL acceptable callback
to exportfs_decode_fh().
While the case described above is a strange corner case that does not
really need to be optimized, the API added for this optimization will
be used by a following patch to optimize a more common case of decoding
an overlayfs file handle.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/exportfs/expfs.c | 9 +++++++++
fs/overlayfs/export.c | 4 ++--
fs/overlayfs/namei.c | 16 +++++++++-------
fs/overlayfs/overlayfs.h | 5 +++--
4 files changed, 23 insertions(+), 11 deletions(-)
diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 329a5d103846..645158dc33f1 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -435,6 +435,15 @@ struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
if (IS_ERR_OR_NULL(result))
return ERR_PTR(-ESTALE);
+ /*
+ * If no acceptance criteria was specified by caller, a disconnected
+ * dentry is also accepatable. Callers may use this mode to query if
+ * file handle is stale or to get a reference to an inode without
+ * risking the high overhead caused by directory reconnect.
+ */
+ if (!acceptable)
+ return result;
+
if (d_is_dir(result)) {
/*
* This request is for a directory.
diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index e688cf019460..15411350a7a1 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -685,7 +685,7 @@ static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
if (!ofs->upper_mnt)
return ERR_PTR(-EACCES);
- upper = ovl_decode_real_fh(fh, ofs->upper_mnt);
+ upper = ovl_decode_real_fh(fh, ofs->upper_mnt, true);
if (IS_ERR_OR_NULL(upper))
return upper;
@@ -735,7 +735,7 @@ static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
}
/* Then lookup origin by fh */
- err = ovl_check_origin_fh(ofs, fh, NULL, &stack);
+ err = ovl_check_origin_fh(ofs, fh, true, NULL, &stack);
if (err) {
goto out_err;
} else if (index) {
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 6e31a4f9e47f..e62e06c735ef 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -179,7 +179,8 @@ static struct ovl_fh *ovl_get_fh(struct dentry *dentry, const char *name)
goto out;
}
-struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt)
+struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
+ bool connected)
{
struct dentry *real;
int bytes;
@@ -194,7 +195,7 @@ struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt)
bytes = (fh->len - offsetof(struct ovl_fh, fid));
real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
bytes >> 2, (int)fh->type,
- ovl_acceptable, mnt);
+ connected ? ovl_acceptable : NULL, mnt);
if (IS_ERR(real)) {
/*
* Treat stale file handle to lower file as "origin unknown".
@@ -320,14 +321,15 @@ static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
}
-int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
+int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
struct dentry *upperdentry, struct ovl_path **stackp)
{
struct dentry *origin = NULL;
int i;
for (i = 0; i < ofs->numlower; i++) {
- origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt);
+ origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt,
+ connected);
if (origin)
break;
}
@@ -371,7 +373,7 @@ static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
if (IS_ERR_OR_NULL(fh))
return PTR_ERR(fh);
- err = ovl_check_origin_fh(ofs, fh, upperdentry, stackp);
+ err = ovl_check_origin_fh(ofs, fh, false, upperdentry, stackp);
kfree(fh);
if (err) {
@@ -461,7 +463,7 @@ struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index)
if (IS_ERR_OR_NULL(fh))
return ERR_CAST(fh);
- upper = ovl_decode_real_fh(fh, ofs->upper_mnt);
+ upper = ovl_decode_real_fh(fh, ofs->upper_mnt, true);
kfree(fh);
if (IS_ERR_OR_NULL(upper))
@@ -568,7 +570,7 @@ int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
/* Check if non-dir index is orphan and don't warn before cleaning it */
if (!d_is_dir(index) && d_inode(index)->i_nlink == 1) {
- err = ovl_check_origin_fh(ofs, fh, index, &stack);
+ err = ovl_check_origin_fh(ofs, fh, false, index, &stack);
if (err)
goto fail;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index dd6c10e5a7db..b51613b355c5 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -266,8 +266,9 @@ static inline bool ovl_is_impuredir(struct dentry *dentry)
/* namei.c */
int ovl_check_fh_len(struct ovl_fh *fh, int fh_len);
-struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt);
-int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
+struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
+ bool connected);
+int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
struct dentry *upperdentry, struct ovl_path **stackp);
int ovl_verify_set_fh(struct dentry *dentry, const char *name,
struct dentry *real, bool is_upper, bool set);
--
2.7.4
--
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