On Tue, 2024-10-08 at 15:11 +0200, Amir Goldstein wrote:
> On Tue, Oct 8, 2024 at 1:07 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> >
> > On Mon, 2024-10-07 at 17:26 +0200, Amir Goldstein wrote:
> > > On Wed, Sep 25, 2024 at 11:14 AM Christian Brauner <brauner@xxxxxxxxxx> wrote:
> > > >
> > > > > open_by_handle_at(2) does not have AT_ flags argument, but also, I find
> > > > > it more useful API that encoding a connectable file handle can mandate
> > > > > the resolving of a connected fd, without having to opt-in for a
> > > > > connected fd independently.
> > > >
> > > > This seems the best option to me too if this api is to be added.
> > >
> > > Thanks.
> > >
> > > Jeff, Chuck,
> > >
> > > Any thoughts on this?
> > >
> >
> > Sorry for the delay. I think encoding the new flag into the fh itself
> > is a reasonable approach.
> >
>
> Adding Jan.
> Sorry I forgot to CC you on the patches, but struct file_handle is officially
> a part of fanotify ABI, so your ACK is also needed on this change.
>
> > I'm less thrilled with using bitfields for this, just because I have a
> > general dislike of them, and they aren't implemented the same way on
> > all arches. Would it break ABI if we just turned the handle_type int
> > into two uint16_t's instead?
>
> I think it will because this will not be backward compat on LE arch:
>
> struct file_handle {
> __u32 handle_bytes;
> - int handle_type;
> + __u16 handle_type;
> + __u16 handle_flags;
> /* file identifier */
> unsigned char f_handle[] __counted_by(handle_bytes);
> };
>
Ok, good point.
> But I can also do without the bitfileds, maybe it's better this way.
> See diff from v2:
>
> diff --git a/fs/fhandle.c b/fs/fhandle.c
> index 4ce4ffddec62..64d44fc61d43 100644
> --- a/fs/fhandle.c
> +++ b/fs/fhandle.c
> @@ -87,9 +87,9 @@ static long do_sys_name_to_handle(const struct path *path,
> * decoding connectable non-directory file handles.
> */
> if (fh_flags & EXPORT_FH_CONNECTABLE) {
> + handle->handle_type |= FILEID_IS_CONNECTABLE;
> if (d_is_dir(path->dentry))
> - fh_flags |= EXPORT_FH_DIR_ONLY;
> - handle->handle_flags = fh_flags;
> + fh_flags |= FILEID_IS_DIR;
> }
> retval = 0;
> }
> @@ -352,7 +352,7 @@ static int handle_to_path(int mountdirfd, struct
> file_handle __user *ufh,
> retval = -EINVAL;
> goto out_path;
> }
> - if (f_handle.handle_flags & ~EXPORT_FH_USER_FLAGS) {
> + if (!FILEID_USER_TYPE_IS_VALID(f_handle.handle_type)) {
> retval = -EINVAL;
> goto out_path;
> }
> @@ -377,10 +377,14 @@ static int handle_to_path(int mountdirfd, struct
> file_handle __user *ufh,
> * are decoding an fd with connected path, which is accessible from
> * the mount fd path.
> */
> - ctx.fh_flags |= f_handle.handle_flags;
> - if (ctx.fh_flags & EXPORT_FH_CONNECTABLE)
> + if (f_handle.handle_type & FILEID_IS_CONNECTABLE) {
> + ctx.fh_flags |= EXPORT_FH_CONNECTABLE;
> ctx.flags |= HANDLE_CHECK_SUBTREE;
> -
> + if (f_handle.handle_type & FILEID_IS_DIR)
> + ctx.fh_flags |= EXPORT_FH_DIR_ONLY;
> + }
> + /* Filesystem code should not be exposed to user flags */
> + handle->handle_type &= ~FILEID_USER_FLAGS_MASK;
> retval = do_handle_to_path(handle, path, &ctx);
>
> out_handle:
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index 96b62e502f71..3e60bac74fa3 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -159,8 +159,17 @@ struct fid {
> #define EXPORT_FH_CONNECTABLE 0x1 /* Encode file handle with parent */
> #define EXPORT_FH_FID 0x2 /* File handle may be non-decodeable */
> #define EXPORT_FH_DIR_ONLY 0x4 /* Only decode file handle for a
> directory */
> -/* Flags allowed in encoded handle_flags that is exported to user */
> -#define EXPORT_FH_USER_FLAGS (EXPORT_FH_CONNECTABLE | EXPORT_FH_DIR_ONLY)
Maybe add a nice comment here about how the handle_type word is
partitioned?
> +
> +/* Flags supported in encoded handle_type that is exported to user */
> +#define FILEID_USER_FLAGS_MASK 0xffff0000
> +#define FILEID_USER_FLAGS(type) ((type) & FILEID_USER_FLAGS_MASK)
> +
> +#define FILEID_IS_CONNECTABLE 0x10000
> +#define FILEID_IS_DIR 0x40000
> +#define FILEID_VALID_USER_FLAGS (FILEID_IS_CONNECTABLE | FILEID_IS_DIR)
> +
> +#define FILEID_USER_TYPE_IS_VALID(type) \
> + (FILEID_USER_FLAGS(type) & ~FILEID_VALID_USER_FLAGS)
>
> /**
> * struct export_operations - for nfsd to communicate with file systems
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index cca7e575d1f8..6329fec40872 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1071,8 +1071,7 @@ struct file {
>
> struct file_handle {
> __u32 handle_bytes;
> - int handle_type:16;
> - int handle_flags:16;
> + int handle_type;
> /* file identifier */
> unsigned char f_handle[] __counted_by(handle_bytes);
> };
I like that better than bitfields, fwiw.
--
Jeff Layton <jlayton@xxxxxxxxxx>
