lpfs 0.2.0

//! /proc/[pid]/fd/ 
//! 
//! <pre> 
//! > This is a subdirectory containing one entry for each file
//! > which the process has open, named by its file descriptor, and
//! > which is a symbolic link to the actual file.  Thus, 0 is stan‐
//! > dard input, 1 standard output, 2 standard error, and so on.
//! > 
//! > For file descriptors for pipes and sockets, the entries will
//! > be symbolic links whose content is the file type with the
//! > inode.  A readlink(2) call on this file returns a string in
//! > the format:
//! >
//! >     type:[inode]
//! > 
//! > For example, socket:[2248868] will be a socket and its inode
//! > is 2248868.  For sockets, that inode can be used to find more
//! > information in one of the files under /proc/net/.
//! > 
//! > For file descriptors that have no corresponding inode (e.g.,
//! > file descriptors produced by bpf(2), epoll_create(2),
//! > eventfd(2), inotify_init(2), perf_event_open(2), signalfd(2),
//! > timerfd_create(2), and userfaultfd(2)), the entry will be a
//! > symbolic link with contents of the form
//! > 
//! >     anon_inode:<file-type>
//! > 
//! > In many cases (but not all), the file-type is surrounded by
//! > square brackets.
//! > 
//! > For example, an epoll file descriptor will have a symbolic
//! > link whose content is the string anon_inode:[eventpoll].
//! > 
//! > In a multithreaded process, the contents of this directory are
//! > not available if the main thread has already terminated (typi‐
//! > cally by calling pthread_exit(3)).
//! > 
//! > Programs that take a filename as a command-line argument, but
//! > don't take input from standard input if no argument is sup‐
//! > plied, and programs that write to a file named as a command-
//! > line argument, but don't send their output to standard output
//! > if no argument is supplied, can nevertheless be made to use
//! > standard input or standard output by using /proc/[pid]/fd
//! > files as command-line arguments.  For example, assuming that
//! > -i is the flag designating an input file and -o is the flag
//! > designating an output file:
//! > 
//! >     $ foobar -i /proc/self/fd/0 -o /proc/self/fd/1 ...
//! > 
//! > and you have a working filter.
//! > 
//! > /proc/self/fd/N is approximately the same as /dev/fd/N in some
//! > UNIX and UNIX-like systems.  Most Linux MAKEDEV scripts sym‐
//! > bolically link /dev/fd to /proc/self/fd, in fact.
//! > 
//! > Most systems provide symbolic links /dev/stdin, /dev/stdout,
//! > and /dev/stderr, which respectively link to the files 0, 1,
//! > and 2 in /proc/self/fd.  Thus the example command above could
//! > be written as:
//! > 
//! >     $ foobar -i /dev/stdin -o /dev/stdout ...
//! > 
//! > Permission to dereference or read (readlink(2)) the symbolic
//! > links in this directory is governed by a ptrace access mode
//! > PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
//! > 
//! > Note that for file descriptors referring to inodes (pipes and
//! > sockets, see above), those inodes still have permission bits
//! > and ownership information distinct from those of the
//! > /proc/[pid]/fd entry, and that the owner may differ from the
//! > user and group IDs of the process.  An unprivileged process
//! > may lack permissions to open them, as in this example:
//! > 
//! >     $ echo test | sudo -u nobody cat
//! >     test
//! >     $ echo test | sudo -u nobody cat /proc/self/fd/0
//! >     cat: /proc/self/fd/0: Permission denied
//! > 
//! > File descriptor 0 refers to the pipe created by the shell and
//! > owned by that shell's user, which is not nobody, so cat does
//! > not have permission to create a new file descriptor to read
//! > from that inode, even though it can still read from its exist‐
//! > ing file descriptor 0.
//! > 
//! > </pre>
//! > -- http://man7.org/linux/man-pages/man5/proc.5.html
//! 

//! > fd — A directory containing all of the file descriptors for a particular process. These are given in numbered links:
//! > total 0
//! > lrwx------    1 root     root           64 May  8 11:31 0 -> /dev/null
//! > lrwx------    1 root     root           64 May  8 11:31 1 -> /dev/null
//! > lrwx------    1 root     root           64 May  8 11:31 2 -> /dev/null
//! > lrwx------    1 root     root           64 May  8 11:31 3 -> /dev/ptmx
//! > lrwx------    1 root     root           64 May  8 11:31 4 -> socket:[7774817]
//! > lrwx------    1 root     root           64 May  8 11:31 5 -> /dev/ptmx
//! > lrwx------    1 root     root           64 May  8 11:31 6 -> socket:[7774829]
//! > lrwx------    1 root     root           64 May  8 11:31 7 -> /dev/ptmx
//! > 
//! > -- https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/deployment_guide/s1-proc-directories#s2-proc-processdirs
 

type Result<T> = std::result::Result<T, crate::ProcErr>;

macro_rules! fd_impl {
    ($path: expr) => {
        let dir_entries = std::fs::read_dir($path)?;
        let mut ret = vec![];
    
        for task_dir in dir_entries {
            let fd_str = task_dir?.file_name();
            let fd = fd_str
                .to_str()
                .ok_or_else(||"contains non-unicode chatacter")?
                .parse::<u32>()?;
            ret.push(fd);
        }
    
        Ok(ret)
    };
}

pub fn fd_of(pid: u32) -> Result<Vec<u32>> {
    fd_impl!{format!("/proc/{}/fd", pid)}
}

pub fn fd_self() -> Result<Vec<u32>> {
    fd_impl!{"/proc/self/fd"}
}

pub fn fd_of_task(pid: u32, tid: u32) -> Result<Vec<u32>> {
    fd_impl!{format!("/proc/{}/task/{}/fd", pid, tid)}
}

pub fn fd_self_task(tid: u32) -> Result<Vec<u32>> {
    fd_impl!{format!("/proc/self/task/{}/fd", tid)}
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_fd() {
        let ret = fd_self().unwrap();
        assert!(ret.contains(&0));
        assert!(ret.contains(&1));
        assert!(ret.contains(&2));
    }
}