On Fri, Oct 29, 2021 at 01:37:49AM +0300, Amir Goldstein wrote:
> On Thu, Oct 28, 2021 at 11:41 PM Georg Müller <georgmueller@xxxxxxx> wrote:
> >
> > Hi,
> >
> > I was trying to implement .tmpfile for overlayfs inode_operations to support O_TMPFILE.
> >
> > Docker with aufs supports it, but this is deprecated and removed from current docker. I now have a work-around in my code (create tmpfile+unlink), but
> > I thought it might be a good idea to have tmpfile support in overlayfs.
> >
> > I was trying to do it on my own, but I have some headaches to what is necessary to achieve the goal.
> >
> > From my understanding, I have to find the dentry for the upper dir (or workdir) and call vfs_tmpdir() for this, but I am running from oops to oops.
> >
> > Is there some hint what I have to do to achieve the goal?
> >
>
> You'd want to use ovl_create_object() and probably pass a tmpfile argument
> then pass it on struct ovl_cattr to ovl_create_or_link() after that
> it becomes more complicated. You'd need ovl_create_tempfile() like
> ovl_create_upper().
> You can follow xfs_generic_create() for some clues.
> You need parts of ovl_instantiate() but not all of it - it's a mess.
Here's something I prepared earlier ;)
Don't know why it got stuck, quite possibly I realized some fatal flaw that I
can't remember anymore...
Seems to work though, so getting this out for review and testing.
Thanks,
Miklos
---
fs/overlayfs/dir.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 122 insertions(+)
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -1295,6 +1295,127 @@ static int ovl_rename(struct user_namesp
return err;
}
+static int ovl_create_upper_tmpfile(struct dentry *dentry, struct inode *inode,
+ umode_t mode)
+{
+ struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
+ struct dentry *newdentry;
+ struct ovl_inode_params oip;
+
+ if (!IS_POSIXACL(d_inode(upperdir)))
+ mode &= ~current_umask();
+
+ newdentry = vfs_tmpfile(&init_user_ns, upperdir, mode, 0);
+ if (IS_ERR(newdentry))
+ return PTR_ERR(newdentry);
+
+ oip = (struct ovl_inode_params) {
+ .upperdentry = newdentry,
+ .newinode = inode,
+ };
+
+ ovl_dentry_set_upper_alias(dentry);
+ ovl_dentry_update_reval(dentry, newdentry,
+ DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
+
+ /*
+ * ovl_obtain_alias() can be called after ovl_create_real()
+ * and before we get here, so we may get an inode from cache
+ * with the same real upperdentry that is not the inode we
+ * pre-allocated. In this case we will use the cached inode
+ * to instantiate the new dentry.
+ */
+ inode = ovl_get_inode(dentry->d_sb, &oip);
+ if (IS_ERR(inode)) {
+ dput(newdentry);
+ return PTR_ERR(inode);
+ }
+ /* d_tmpfile() expects inode to have a positive link count */
+ set_nlink(inode, 1);
+
+ d_tmpfile(dentry, inode);
+ if (inode != oip.newinode) {
+ pr_warn_ratelimited("newly created inode found in cache (%pd2)\n",
+ dentry);
+ }
+ return 0;
+}
+
+static int ovl_create_tmpfile(struct dentry *dentry, struct inode *inode,
+ umode_t mode)
+{
+ int err;
+ const struct cred *old_cred;
+ struct cred *override_cred;
+ struct dentry *parent = dentry->d_parent;
+
+ err = ovl_copy_up(parent);
+ if (err)
+ return err;
+
+ old_cred = ovl_override_creds(dentry->d_sb);
+
+ err = -ENOMEM;
+ override_cred = prepare_creds();
+ if (override_cred) {
+ override_cred->fsuid = inode->i_uid;
+ override_cred->fsgid = inode->i_gid;
+ err = security_dentry_create_files_as(dentry, mode,
+ &dentry->d_name, old_cred,
+ override_cred);
+ if (err) {
+ put_cred(override_cred);
+ goto out_revert_creds;
+ }
+ put_cred(override_creds(override_cred));
+ put_cred(override_cred);
+
+ err = ovl_create_upper_tmpfile(dentry, inode, mode);
+ }
+out_revert_creds:
+ revert_creds(old_cred);
+ return err;
+}
+
+
+static int ovl_tmpfile(struct user_namespace *mnt_userns, struct inode *dir,
+ struct dentry *dentry, umode_t mode)
+{
+ int err;
+ struct inode *inode;
+
+ dentry->d_fsdata = ovl_alloc_entry(0);
+ if (!dentry->d_fsdata)
+ return -ENOMEM;
+
+ err = ovl_want_write(dentry);
+ if (err)
+ goto out;
+
+ /* Preallocate inode to be used by ovl_get_inode() */
+ err = -ENOMEM;
+ inode = ovl_new_inode(dentry->d_sb, mode, 0);
+ if (!inode)
+ goto out_drop_write;
+
+ spin_lock(&inode->i_lock);
+ inode->i_state |= I_CREATING;
+ spin_unlock(&inode->i_lock);
+
+ inode_init_owner(&init_user_ns, inode, dentry->d_parent->d_inode, mode);
+ mode = inode->i_mode;
+
+ err = ovl_create_tmpfile(dentry, inode, mode);
+ /* Did we end up using the preallocated inode? */
+ if (inode != d_inode(dentry))
+ iput(inode);
+
+out_drop_write:
+ ovl_drop_write(dentry);
+out:
+ return err;
+}
+
const struct inode_operations ovl_dir_inode_operations = {
.lookup = ovl_lookup,
.mkdir = ovl_mkdir,
@@ -1313,4 +1434,5 @@ const struct inode_operations ovl_dir_in
.update_time = ovl_update_time,
.fileattr_get = ovl_fileattr_get,
.fileattr_set = ovl_fileattr_set,
+ .tmpfile = ovl_tmpfile,
};
