ovl: check if upperdir fs supports O_TMPFILE

This is needed for choosing between concurrent copyup
using O_TMPFILE and legacy copyup using workdir+rename.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

3 files changed, 20 insertions, 0 deletions

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 8af450b0e57a..3822a909ce1f 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -127,6 +127,15 @@ static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
         return err;
 }
 
+static inline struct dentry *ovl_do_tmpfile(struct dentry *dentry, umode_t mode)
+{
+        struct dentry *ret = vfs_tmpfile(dentry, mode, 0);
+        int err = IS_ERR(ret) ? PTR_ERR(ret) : 0;
+
+        pr_debug("tmpfile(%pd2, 0%o) = %i\n", dentry, mode, err);
+        return ret;
+}
+
 static inline struct inode *ovl_inode_real(struct inode *inode, bool *is_upper)
 {
         unsigned long x = (unsigned long) READ_ONCE(inode->i_private);
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index d14bca1850d9..65f240001aa6 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -27,6 +27,7 @@ struct ovl_fs {
         struct ovl_config config;
         /* creds of process who forced instantiation of super block */
         const struct cred *creator_cred;
+        bool tmpfile;
 };
 
 /* private information held for every overlayfs dentry */
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 20f48abbb82f..ff05065b510f 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -825,6 +825,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                  * creation of workdir in previous step.
                  */
                 if (ufs->workdir) {
+                        struct dentry *temp;
+
                         err = ovl_check_d_type_supported(&workpath);
                         if (err < 0)
                                 goto out_put_workdir;
@@ -836,6 +838,14 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                          */
                         if (!err)
                                 pr_warn("overlayfs: upper fs needs to support d_type.\n");
+
+                        /* Check if upper/work fs supports O_TMPFILE */
+                        temp = ovl_do_tmpfile(ufs->workdir, S_IFREG | 0);
+                        ufs->tmpfile = !IS_ERR(temp);
+                        if (ufs->tmpfile)
+                                dput(temp);
+                        else
+                                pr_warn("overlayfs: upper fs does not support tmpfile.\n");
                 }
         }