crosvm: move kernel_cmdline to it's own crate

We'll want architecture code to be able to supply and manipulate Linux
kernel command lines, so let's move this out to it's own crate and
export the interfaces.

BUG=chromium:797868
TEST=./build_test passes on all architectures
TEST=crosvm runs on caroline

Change-Id: I94904055ac02582a4f4d8bbb54d0f41ed14b955d
Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/898351
Reviewed-by: Dylan Reid <dgreid@chromium.org>

2 files changed, 237 insertions, 0 deletions

diff --git a/kernel_cmdline/Cargo.toml b/kernel_cmdline/Cargo.toml
new file mode 100644
index 0000000..03c4338
--- /dev/null
+++ b/kernel_cmdline/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "kernel_cmdline"
+version = "0.1.0"
+
+[dependencies]
+libc = "*"
+
+[lib]
+path = "src/kernel_cmdline.rs"
diff --git a/kernel_cmdline/src/kernel_cmdline.rs b/kernel_cmdline/src/kernel_cmdline.rs
new file mode 100644
index 0000000..db6dffa
--- /dev/null
+++ b/kernel_cmdline/src/kernel_cmdline.rs
@@ -0,0 +1,228 @@
+// Copyright 2017 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+//! Helper for creating valid kernel command line strings.
+
+use std::result;
+use std::fmt;
+
+/// The error type for command line building operations.
+#[derive(PartialEq, Debug)]
+pub enum Error {
+    /// Operation would have resulted in a non-printable ASCII character.
+    InvalidAscii,
+    /// Key/Value Operation would have had a space in it.
+    HasSpace,
+    /// Key/Value Operation would have had an equals sign in it.
+    HasEquals,
+    /// Operation would have made the command line too large.
+    TooLarge,
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f,
+               "{}",
+               match *self {
+                   Error::InvalidAscii => "string contains non-printable ASCII character",
+                   Error::HasSpace => "string contains a space",
+                   Error::HasEquals => "string contains an equals sign",
+                   Error::TooLarge => "inserting string would make command line too long",
+               })
+    }
+}
+
+/// Specialized Result type for command line operations.
+pub type Result<T> = result::Result<T, Error>;
+
+fn valid_char(c: char) -> bool {
+    match c {
+        ' '...'~' => true,
+        _ => false,
+    }
+}
+
+fn valid_str(s: &str) -> Result<()> {
+    if s.chars().all(valid_char) {
+        Ok(())
+    } else {
+        Err(Error::InvalidAscii)
+    }
+}
+
+fn valid_element(s: &str) -> Result<()> {
+    if !s.chars().all(valid_char) {
+        Err(Error::InvalidAscii)
+    } else if s.contains(' ') {
+        Err(Error::HasSpace)
+    } else if s.contains('=') {
+        Err(Error::HasEquals)
+    } else {
+        Ok(())
+    }
+}
+
+/// A builder for a kernel command line string that validates the string as its being built. A
+/// `CString` can be constructed from this directly using `CString::new`.
+pub struct Cmdline {
+    line: String,
+    capacity: usize,
+}
+
+impl Cmdline {
+    /// Constructs an empty Cmdline with the given capacity, which includes the nul terminator.
+    /// Capacity must be greater than 0.
+    pub fn new(capacity: usize) -> Cmdline {
+        assert_ne!(capacity, 0);
+        Cmdline {
+            line: String::new(),
+            capacity: capacity,
+        }
+    }
+
+    fn has_capacity(&self, more: usize) -> Result<()> {
+        let needs_space = if self.line.is_empty() { 0 } else { 1 };
+        if self.line.len() + more + needs_space < self.capacity {
+            Ok(())
+        } else {
+            Err(Error::TooLarge)
+        }
+    }
+
+    fn start_push(&mut self) {
+        if !self.line.is_empty() {
+            self.line.push(' ');
+        }
+    }
+
+    fn end_push(&mut self) {
+        // This assert is always true because of the `has_capacity` check that each insert method
+        // uses.
+        assert!(self.line.len() < self.capacity);
+    }
+
+    /// Validates and inserts a key value pair into this command line
+    pub fn insert<T: AsRef<str>>(&mut self, key: T, val: T) -> Result<()> {
+        let k = key.as_ref();
+        let v = val.as_ref();
+
+        valid_element(k)?;
+        valid_element(v)?;
+        self.has_capacity(k.len() + v.len() + 1)?;
+
+        self.start_push();
+        self.line.push_str(k);
+        self.line.push('=');
+        self.line.push_str(v);
+        self.end_push();
+
+        Ok(())
+    }
+
+    /// Validates and inserts a string to the end of the current command line
+    pub fn insert_str<T: AsRef<str>>(&mut self, slug: T) -> Result<()> {
+        let s = slug.as_ref();
+        valid_str(s)?;
+
+        self.has_capacity(s.len())?;
+
+        self.start_push();
+        self.line.push_str(s);
+        self.end_push();
+
+        Ok(())
+    }
+
+    /// Returns the cmdline in progress without nul termination
+    pub fn as_str(&self) -> &str {
+        self.line.as_str()
+    }
+}
+
+impl Into<Vec<u8>> for Cmdline {
+    fn into(self) -> Vec<u8> {
+        self.line.into_bytes()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::ffi::CString;
+
+    #[test]
+    fn insert_hello_world() {
+        let mut cl = Cmdline::new(100);
+        assert_eq!(cl.as_str(), "");
+        assert!(cl.insert("hello", "world").is_ok());
+        assert_eq!(cl.as_str(), "hello=world");
+
+        let s = CString::new(cl).expect("failed to create CString from Cmdline");
+        assert_eq!(s, CString::new("hello=world").unwrap());
+    }
+
+    #[test]
+    fn insert_multi() {
+        let mut cl = Cmdline::new(100);
+        assert!(cl.insert("hello", "world").is_ok());
+        assert!(cl.insert("foo", "bar").is_ok());
+        assert_eq!(cl.as_str(), "hello=world foo=bar");
+    }
+
+    #[test]
+    fn insert_space() {
+        let mut cl = Cmdline::new(100);
+        assert_eq!(cl.insert("a ", "b"), Err(Error::HasSpace));
+        assert_eq!(cl.insert("a", "b "), Err(Error::HasSpace));
+        assert_eq!(cl.insert("a ", "b "), Err(Error::HasSpace));
+        assert_eq!(cl.insert(" a", "b"), Err(Error::HasSpace));
+        assert_eq!(cl.as_str(), "");
+    }
+
+    #[test]
+    fn insert_equals() {
+        let mut cl = Cmdline::new(100);
+        assert_eq!(cl.insert("a=", "b"), Err(Error::HasEquals));
+        assert_eq!(cl.insert("a", "b="), Err(Error::HasEquals));
+        assert_eq!(cl.insert("a=", "b "), Err(Error::HasEquals));
+        assert_eq!(cl.insert("=a", "b"), Err(Error::HasEquals));
+        assert_eq!(cl.insert("a", "=b"), Err(Error::HasEquals));
+        assert_eq!(cl.as_str(), "");
+    }
+
+    #[test]
+    fn insert_emoji() {
+        let mut cl = Cmdline::new(100);
+        assert_eq!(cl.insert("heart", "💖"), Err(Error::InvalidAscii));
+        assert_eq!(cl.insert("💖", "love"), Err(Error::InvalidAscii));
+        assert_eq!(cl.as_str(), "");
+    }
+
+    #[test]
+    fn insert_string() {
+        let mut cl = Cmdline::new(13);
+        assert_eq!(cl.as_str(), "");
+        assert!(cl.insert_str("noapic").is_ok());
+        assert_eq!(cl.as_str(), "noapic");
+        assert!(cl.insert_str("nopci").is_ok());
+        assert_eq!(cl.as_str(), "noapic nopci");
+    }
+
+    #[test]
+    fn insert_too_large() {
+        let mut cl = Cmdline::new(4);
+        assert_eq!(cl.insert("hello", "world"), Err(Error::TooLarge));
+        assert_eq!(cl.insert("a", "world"), Err(Error::TooLarge));
+        assert_eq!(cl.insert("hello", "b"), Err(Error::TooLarge));
+        assert!(cl.insert("a", "b").is_ok());
+        assert_eq!(cl.insert("a", "b"), Err(Error::TooLarge));
+        assert_eq!(cl.insert_str("a"), Err(Error::TooLarge));
+        assert_eq!(cl.as_str(), "a=b");
+
+        let mut cl = Cmdline::new(10);
+        assert!(cl.insert("ab", "ba").is_ok()); // adds 5 length
+        assert_eq!(cl.insert("c", "da"), Err(Error::TooLarge)); // adds 5 (including space) length
+        assert!(cl.insert("c", "d").is_ok()); // adds 4 (including space) length
+    }
+}