On Fri, Aug 15, 2025 at 1:51 AM Thomas Bertschinger
<tahbertschinger@xxxxxxxxx> wrote:
>
> Create a helper do_name_to_handle_at() that takes an additional argument,
> lookup_flags, beyond the syscall arguments.
>
> Because name_to_handle_at(2) doesn't take any lookup flags, it always
> passes 0 for this argument.
>
> Future callers like io_uring may pass LOOKUP_CACHED in order to request
> a non-blocking lookup.
>
> This helper's name is confusingly similar to do_sys_name_to_handle()
> which takes care of returning the file handle, once the filename has
> been turned into a struct path. To distinguish the names more clearly,
> rename the latter to do_path_to_handle().
>
> Signed-off-by: Thomas Bertschinger <tahbertschinger@xxxxxxxxx>
> ---
> fs/fhandle.c | 61 ++++++++++++++++++++++++++++-----------------------
> fs/internal.h | 7 ++++++
> 2 files changed, 41 insertions(+), 27 deletions(-)
>
> diff --git a/fs/fhandle.c b/fs/fhandle.c
> index 7c236f64cdea..57da648ca866 100644
> --- a/fs/fhandle.c
> +++ b/fs/fhandle.c
> @@ -14,10 +14,10 @@
> #include "internal.h"
> #include "mount.h"
>
> -static long do_sys_name_to_handle(const struct path *path,
> - struct file_handle __user *ufh,
> - void __user *mnt_id, bool unique_mntid,
> - int fh_flags)
> +static long do_path_to_handle(const struct path *path,
> + struct file_handle __user *ufh,
> + void __user *mnt_id, bool unique_mntid,
> + int fh_flags)
> {
> long retval;
> struct file_handle f_handle;
> @@ -111,27 +111,11 @@ static long do_sys_name_to_handle(const struct path *path,
> return retval;
> }
>
> -/**
> - * sys_name_to_handle_at: convert name to handle
> - * @dfd: directory relative to which name is interpreted if not absolute
> - * @name: name that should be converted to handle.
> - * @handle: resulting file handle
> - * @mnt_id: mount id of the file system containing the file
> - * (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
> - * @flag: flag value to indicate whether to follow symlink or not
> - * and whether a decodable file handle is required.
> - *
> - * @handle->handle_size indicate the space available to store the
> - * variable part of the file handle in bytes. If there is not
> - * enough space, the field is updated to return the minimum
> - * value required.
> - */
> -SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
> - struct file_handle __user *, handle, void __user *, mnt_id,
> - int, flag)
> +long do_name_to_handle_at(int dfd, const char __user *name,
> + struct file_handle __user *handle, void __user *mnt_id,
> + int flag, int lookup_flags)
> {
> struct path path;
> - int lookup_flags;
> int fh_flags = 0;
> int err;
>
> @@ -155,19 +139,42 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
> else if (flag & AT_HANDLE_CONNECTABLE)
> fh_flags |= EXPORT_FH_CONNECTABLE;
>
> - lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
> + if (flag & AT_SYMLINK_FOLLOW)
> + lookup_flags |= LOOKUP_FOLLOW;
> if (flag & AT_EMPTY_PATH)
> lookup_flags |= LOOKUP_EMPTY;
> err = user_path_at(dfd, name, lookup_flags, &path);
> if (!err) {
> - err = do_sys_name_to_handle(&path, handle, mnt_id,
> - flag & AT_HANDLE_MNT_ID_UNIQUE,
> - fh_flags);
> + err = do_path_to_handle(&path, handle, mnt_id,
> + flag & AT_HANDLE_MNT_ID_UNIQUE,
> + fh_flags);
> path_put(&path);
> }
> return err;
> }
>
> +/**
> + * sys_name_to_handle_at: convert name to handle
> + * @dfd: directory relative to which name is interpreted if not absolute
> + * @name: name that should be converted to handle.
> + * @handle: resulting file handle
> + * @mnt_id: mount id of the file system containing the file
> + * (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
> + * @flag: flag value to indicate whether to follow symlink or not
> + * and whether a decodable file handle is required.
> + *
> + * @handle->handle_size indicate the space available to store the
> + * variable part of the file handle in bytes. If there is not
> + * enough space, the field is updated to return the minimum
> + * value required.
> + */
> +SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
> + struct file_handle __user *, handle, void __user *, mnt_id,
> + int, flag)
> +{
> + return do_name_to_handle_at(dfd, name, handle, mnt_id, flag, 0);
> +}
> +
> static int get_path_anchor(int fd, struct path *root)
> {
> if (fd >= 0) {
> diff --git a/fs/internal.h b/fs/internal.h
> index 38e8aab27bbd..af7e0810a90d 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -355,3 +355,10 @@ int anon_inode_getattr(struct mnt_idmap *idmap, const struct path *path,
> int anon_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> struct iattr *attr);
> void pidfs_get_root(struct path *path);
> +
> +/*
> + * fs/fhandle.c
> + */
> +long do_name_to_handle_at(int dfd, const char __user *name,
> + struct file_handle __user *handle,
> + void __user *mnt_id, int flag, int lookup_flags);
I really dislike do_XXX() helpers because we use them interchangeably
sometimes to wrap vfs_XXX() helpers and sometimes the other way around,
so exporting them in the vfs internal interface is a very bad pattern IMO.
io_uring has a common pattern that requires a helper with all the syscall
args and for that purpose, it uses do_renameat2(), do_unlinkat(), ...
I would much rather that we stop this pattern and start with following
the do_sys_XXX() pattern as in the do_sys_ftruncate() helper.
Lucky for us, you just renamed the confusing helper named
do_sys_name_to_handle(), so you are free to reuse this name
(+ _at) in a non confusing placement.
Thanks,
Amir.
