df: /run/user/1000/doc: Operation not permitted (os error 1)

[fox0]

Describe the bug
df not work

To Reproduce
Steps to reproduce the behavior:

1. Run strace target/debug/df

newfstatat(AT_FDCWD, "/run/user/1000", {st_mode=S_IFDIR|0700, st_size=420, ...}, 0) = 0
statfs("/run/user/1000/doc", 0x7fff0b3dbe98) = -1 EPERM (Операция не позволена)

$ mount | grep '/run/user/1000/'
portal on /run/user/1000/doc type fuse.portal (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000)

Operaing system (OS) info:

$ uname -a
Linux deb12 6.9.7+bpo-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.9.7-1~bpo12+1 (2024-07-03) x86_64 GNU/Linux
$ cat /etc/debian_version 
12.7

Patch:

                let rc = libc::statfs(me.mnt_dir, &mut mount);
                if rc < 0 {
                    eprintln!("{}: {}", String::from(dirname.to_str().unwrap()), io::Error::last_os_error());
                    continue;  // <--
                }

or fox0@2806bb7

[jgarzik]

Would you be willing to submit a PR?

Your other changes are welcome to be considered as well. Just please put new features and cleanups in separate commits from bug fixes. (See Linux kernel expert talk about this in https://github.com/axboe/liburing/blob/master/CONTRIBUTING.md)