linux-kernel - Re: [PATCH v3 3/3] fs: fuse: add more information to fdinfo

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Message-ID: <CAC1kPDOdDdPQVKs0C-LmgT1_MGBWbFqy4F+5TeunYBkA=xq7+Q@mail.gmail.com>
Date: Fri, 9 May 2025 14:40:14 +0800
From: Chen Linxuan <chenlinxuan@...ontech.com>
To: chenlinxuan@...ontech.com
Cc: Miklos Szeredi <miklos@...redi.hu>, Amir Goldstein <amir73il@...il.com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] fs: fuse: add more information to fdinfo

On Fri, May 9, 2025 at 2:34 PM Chen Linxuan via B4 Relay
<devnull+chenlinxuan.uniontech.com@...nel.org> wrote:
>
> From: Chen Linxuan <chenlinxuan@...ontech.com>
>
> This commit add fuse connection device id, open_flags and backing
> files, to fdinfo of opened fuse files.
>
> Related discussions can be found at links below.
>
> Link: https://lore.kernel.org/all/CAOQ4uxgS3OUy9tpphAJKCQFRAn2zTERXXa0QN_KvP6ZOe2KVBw@mail.gmail.com/
> Link: https://lore.kernel.org/all/CAOQ4uxgkg0uOuAWO2wOPNkMmD9wqd5wMX+gTfCT-zVHBC8CkZg@mail.gmail.com/
> Cc: Amir Goldstein <amir73il@...il.com>
> Signed-off-by: Chen Linxuan <chenlinxuan@...ontech.com>
> ---
>  fs/fuse/file.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 754378dd9f7159f20fde6376962d45c4c706b868..1e54965780e9d625918c22a3dea48ba5a9a5ed1b 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -8,6 +8,8 @@
>
>  #include "fuse_i.h"
>
> +#include "linux/idr.h"
> +#include "linux/rcupdate.h"
>  #include <linux/pagemap.h>
>  #include <linux/slab.h>
>  #include <linux/kernel.h>
> @@ -3392,6 +3394,21 @@ static ssize_t fuse_copy_file_range(struct file *src_file, loff_t src_off,
>         return ret;
>  }
>
> +static void fuse_file_show_fdinfo(struct seq_file *seq, struct file *f)
> +{
> +       struct fuse_file *ff = f->private_data;
> +       struct fuse_conn *fc = ff->fm->fc;
> +       struct file *backing_file = fuse_file_passthrough(ff);
> +
> +       seq_printf(seq, "fuse conn:%u open_flags:%u\n", fc->dev, ff->open_flags);

Note: The fc->dev is already accessible to userspace.
The mnt_id field in /proc/PID/fdinfo/FD references a mount,
which can be found in /proc/PID/mountinfo.

And this file includes the device ID.

> +
> +       if (backing_file) {
> +               seq_puts(seq, "fuse backing_file: ");
> +               seq_file_path(seq, backing_file, " \t\n\\");
> +               seq_puts(seq, "\n");
> +       }
> +}
> +
>  static const struct file_operations fuse_file_operations = {
>         .llseek         = fuse_file_llseek,
>         .read_iter      = fuse_file_read_iter,
> @@ -3411,6 +3428,9 @@ static const struct file_operations fuse_file_operations = {
>         .poll           = fuse_file_poll,
>         .fallocate      = fuse_file_fallocate,
>         .copy_file_range = fuse_copy_file_range,
> +#ifdef CONFIG_PROC_FS
> +       .show_fdinfo    = fuse_file_show_fdinfo,
> +#endif
>  };
>
>  static const struct address_space_operations fuse_file_aops  = {
>
> --
> 2.43.0
>
>
>
>