Implement printing a list of SysV IPC mqs

What could be improved is when printing the information to use a
better human readable format.

As usual the readme and the man page are both updated.

README.md

@@ -67,6 +67,10 @@ queue. Following optional arguments are supported:
 - `-m`, `--mode`: Permissions (octal) to create the queue
   with. Default: 0644.
 
+#### List all message queues
+Use the `list` command to print a list of all message queues. No
+further arguments are supported.
+
 #### Delete a message queue
 Use the `unlink` command to delete a message queue. This can either be
 done by providing a `key` or an `id` of the queue:

mqrs.1

@@ -241,6 +241,18 @@ Produce verbose output
 .B \-m, \-\-mode \fI<mode>\fP
 Permissions (octal) to create the queue with (default: 0644)
 .RE
+.SS list [FLAGS]
+Print a list of all existing SysV IPC message queues.
+.TP 8
+.SS FLAGS
+.RS
+.TP 8
+.B \-h, \-\-help
+Prints help information
+.TP 8
+.B \-v, \-\-verbose
+Produce verbose output
+.RE
 .SS unlink [FLAGS] [OPTIONS]
 Delete an existing SysV IPC message queue. It is mandatory to pass
 exactly one OPTION.

src/main.rs

@@ -25,6 +25,7 @@ enum PosixCommand {
 #[derive(Clap, Debug)]
 enum SysvCommand {
     Create(sysv::Create),
+    List(sysv::List),
     Unlink(sysv::Unlink),
 }
 
@@ -69,6 +70,7 @@ fn main() -> Result<()> {
         },
         Backend::Sysv(s) => match s {
             SysvCommand::Create(c) => c.run()?,
+            SysvCommand::List(l) => l.run()?,
             SysvCommand::Unlink(u) => u.run()?,
         },
     }

src/sysv.rs

@@ -1,5 +1,7 @@
 mod create;
+mod list;
 mod unlink;
 
 pub use create::Create;
+pub use list::List;
 pub use unlink::Unlink;

src/sysv/list.rs

@@ -0,0 +1,26 @@
+use anyhow::Result;
+use clap::Clap;
+use std::{
+    fs::File,
+    io::{BufRead, BufReader},
+};
+
+/// Print a list of existing message queues
+#[derive(Clap, Debug)]
+pub struct List {}
+
+impl List {
+    pub fn run(&self) -> Result<()> {
+        let file = BufReader::new(File::open("/proc/sysvipc/msg")?);
+
+        for line in file.lines() {
+            for field in line?.split_whitespace().collect::<Vec<&str>>() {
+                print!("{0: <10}", field);
+            }
+
+            println!();
+        }
+
+        Ok(())
+    }
+}