Re: [PATCH v3 4/9] cachefiles: use tmpfile_open() helper

[Christian Brauner <brauner@xxxxxxxxxx>]

On Tue, Sep 20, 2022 at 09:36:27PM +0200, Miklos Szeredi wrote:
> Use the tmpfile_open() helper instead of doing tmpfile creation and opening
> separately.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
>  fs/cachefiles/namei.c | 26 ++++++++++----------------
>  1 file changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
> index d3a5884fe5c9..44f575328af4 100644
> --- a/fs/cachefiles/namei.c
> +++ b/fs/cachefiles/namei.c
> @@ -451,18 +451,19 @@ struct file *cachefiles_create_tmpfile(struct cachefiles_object *object)
>  	const struct cred *saved_cred;
>  	struct dentry *fan = volume->fanout[(u8)object->cookie->key_hash];
>  	struct file *file;
> -	struct path path;
> +	struct path path = { .mnt = cache->mnt, .dentry = fan };
>  	uint64_t ni_size;
>  	long ret;

Maybe we shouldn't use struct path to first refer to the parent path and
then to the tmp path to avoid any potential confusion and instead rely
on a compount initializer for the tmpfile_open() call (__not tested__)?:

diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index 44f575328af4..979b2f173ac3 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -451,7 +451,7 @@ struct file *cachefiles_create_tmpfile(struct cachefiles_object *object)
        const struct cred *saved_cred;
        struct dentry *fan = volume->fanout[(u8)object->cookie->key_hash];
        struct file *file;
-       struct path path = { .mnt = cache->mnt, .dentry = fan };
+       struct path path;
        uint64_t ni_size;
        long ret;

@@ -460,8 +460,10 @@ struct file *cachefiles_create_tmpfile(struct cachefiles_object *object)

        ret = cachefiles_inject_write_error();
        if (ret == 0) {
-               file = tmpfile_open(&init_user_ns, &path, S_IFREG,
-                                   O_RDWR | O_LARGEFILE | O_DIRECT,
+               file = tmpfile_open(&init_user_ns,
+                                   &{const struct path} {.mnt = cache->mnt,
+                                                         .dentry = fan},
+                                   S_IFREG, O_RDWR | O_LARGEFILE | O_DIRECT,
                                    cache->cache_cred);
                ret = PTR_ERR_OR_ZERO(file);
        }
@@ -472,7 +474,9 @@ struct file *cachefiles_create_tmpfile(struct cachefiles_object *object)
                        cachefiles_io_error_obj(object, "Failed to create tmpfile");
                goto err;
        }
-       /* From now path refers to the tmpfile */
+
+       /* prepare tmp path */
+       path.mnt = cache->mnt;
        path.dentry = file->f_path.dentry;

        trace_cachefiles_tmpfile(object, d_backing_inode(path.dentry));