linux-kernel - Re: [RFC PATCH v2 6/6] fuse: implementation of export_operations with FUSE_LOOKUP

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Message-ID: <CAJfpegu8-ddQeE9nnY5NH64KQHzr1Zfb=187Pb2uw14oTEPdOw@mail.gmail.com>
Date: Tue, 16 Dec 2025 11:58:25 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Luis Henriques <luis@...lia.com>
Cc: Amir Goldstein <amir73il@...il.com>, "Darrick J. Wong" <djwong@...nel.org>, 
	Bernd Schubert <bschubert@....com>, Kevin Chen <kchen@....com>, 
	Horst Birthelmer <hbirthelmer@....com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Matt Harvey <mharvey@...ptrading.com>, 
	kernel-dev@...lia.com
Subject: Re: [RFC PATCH v2 6/6] fuse: implementation of export_operations with FUSE_LOOKUP_HANDLE

On Fri, 12 Dec 2025 at 19:13, Luis Henriques <luis@...lia.com> wrote:
>
> This patch allows the NFS handle to use the new file handle provided by the
> LOOKUP_HANDLE operation.  It still allows the usage of nodeid+generation as
> an handle if this operation is not supported by the FUSE server or if no
> handle is available for a specific inode.  I.e. it can mix both file handle
> types FILEID_INO64_GEN{_PARENT} and FILEID_FUSE_WITH{OUT}_PARENT.
>
> Signed-off-by: Luis Henriques <luis@...lia.com>
> ---
>  fs/fuse/export.c         | 162 ++++++++++++++++++++++++++++++++++++---
>  include/linux/exportfs.h |   7 ++
>  2 files changed, 160 insertions(+), 9 deletions(-)
>
> diff --git a/fs/fuse/export.c b/fs/fuse/export.c
> index 4a9c95fe578e..b40d146a32f2 100644
> --- a/fs/fuse/export.c
> +++ b/fs/fuse/export.c
> @@ -3,6 +3,7 @@
>   * FUSE NFS export support.
>   *
>   * Copyright (C) 2001-2008  Miklos Szeredi <miklos@...redi.hu>
> + * Copyright (C) 2025 Jump Trading LLC, author: Luis Henriques <luis@...lia.com>
>   */
>
>  #include "fuse_i.h"
> @@ -10,7 +11,8 @@
>
>  struct fuse_inode_handle {
>         u64 nodeid;
> -       u32 generation;
> +       u32 generation; /* XXX change to u64, and use fid->i64.ino in encode/decode? */
> +       struct fuse_file_handle fh;
>  };
>
>  static struct dentry *fuse_get_dentry(struct super_block *sb,
> @@ -67,8 +69,8 @@ static struct dentry *fuse_get_dentry(struct super_block *sb,
>         return ERR_PTR(err);
>  }
>
> -static int fuse_encode_fh(struct inode *inode, u32 *fh, int *max_len,
> -                          struct inode *parent)
> +static int fuse_encode_gen_fh(struct inode *inode, u32 *fh, int *max_len,
> +                             struct inode *parent)
>  {
>         int len = parent ? 6 : 3;
>         u64 nodeid;
> @@ -96,38 +98,180 @@ static int fuse_encode_fh(struct inode *inode, u32 *fh, int *max_len,
>         }
>
>         *max_len = len;
> +
>         return parent ? FILEID_INO64_GEN_PARENT : FILEID_INO64_GEN;
>  }
>
> -static struct dentry *fuse_fh_to_dentry(struct super_block *sb,
> -               struct fid *fid, int fh_len, int fh_type)
> +static int fuse_encode_fuse_fh(struct inode *inode, u32 *fh, int *max_len,
> +                              struct inode *parent)
> +{
> +       struct fuse_inode *fi = get_fuse_inode(inode);
> +       struct fuse_inode *fip = NULL;
> +       struct fuse_inode_handle *handle = (void *)fh;
> +       int type = FILEID_FUSE_WITHOUT_PARENT;
> +       int len, lenp = 0;
> +       int buflen = *max_len << 2; /* max_len: number of words */
> +
> +       len = sizeof(struct fuse_inode_handle) + fi->fh->size;
> +       if (parent) {
> +               fip = get_fuse_inode(parent);
> +               if (fip->fh && fip->fh->size) {
> +                       lenp = sizeof(struct fuse_inode_handle) +
> +                               fip->fh->size;
> +                       type = FILEID_FUSE_WITH_PARENT;
> +               }
> +       }
> +
> +       if (buflen < (len + lenp)) {
> +               *max_len = (len + lenp) >> 2;
> +               return  FILEID_INVALID;
> +       }
> +
> +       handle[0].nodeid = fi->nodeid;
> +       handle[0].generation = inode->i_generation;

I think it should be either

  - encode nodeid + generation (backward compatibility),

  - or encode file handle for servers that support it

but not both.

Which means that fuse_iget() must be able to search the cache based on
the handle as well, but that should not be too difficult to implement
(need to hash the file handle).

Thanks,
Miklos