monochromatic-git-policy-cli 0.5.12

//! What:
//!  The filesystem section of `git cli-git doctor`: what the repository's main checkout sits on (btrfs subvolume,
//!  btrfs directory, overlayfs, other), whether the mount allows a regular user to delete a subvolume, and the exact
//!  commands that change what can be changed.
//! Why:
//!  Cheap worktrees need a btrfs subvolume, and deleting a worktree that is a subvolume in one step needs the mount
//!  option `user_subvol_rm_allowed`. Neither is visible to the person until something is slow, so the doctor says what
//!  holds and prints the command, never runs it. Everything is informational: the section goes to standard error after
//!  the hook report and never changes the exit status. It reads `statfs`, one inode number, `/proc/self/mountinfo`,
//!  `/run/ostree-booted` and `/proc/cmdline`, and starts nothing. The facts are gathered apart from the wording
//!  (`FilesystemFacts` in, text out), so the wording is tested on built facts and the exact-output controls of the
//!  doctor and the management command stay independent of the host they run on.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! const section = renderSection(await gatherFacts(mainCheckoutRoot)); // '' when no checkout was found
//! ```

use super::fs_kind::{FilesystemKind, filesystem_kind, is_subvolume_root};
use super::fs_mount_options::read_mount_facts;
use super::shell_quote::shell_quote;
use std::os::unix::ffi::OsStrExt;
use std::path::{Path, PathBuf};

/// The first words of the first line of the section, which a caller can cut the section off at.
pub const SECTION_MARKER: &str = "git cli-git doctor: filesystem:";

/// The mount option that lets a regular user delete a subvolume in one step.
pub const REMOVAL_OPTION: &str = "user_subvol_rm_allowed";

/// The marker file that systemd creates on an ostree or bootc host.
const OSTREE_BOOTED_PATH: &str = "/run/ostree-booted";

/// Where an ostree or bootc host mounts the filesystem that the kernel command line's `root=` and `rootflags=` name; `/`
///  there is a composefs overlay.
const SYSROOT_PATH: &str = "/sysroot";

/// The kernel command line of the running system.
const CMDLINE_PATH: &str = "/proc/cmdline";

/// What:
///  The mount that holds the checkout, reduced to what the section needs.
/// Why:
///   The remount command names the mount point, and the option check reads both option lists of the mount.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type MountSummary = { mountPoint: string; source: string; hasRemovalOption: boolean };
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct MountSummary {
    /// Where the filesystem is mounted.
    pub mount_point: PathBuf,
    /// The device or source the kernel lists for it.
    pub source: String,
    /// Whether `user_subvol_rm_allowed` is among the mount options or the superblock options.
    pub has_removal_option: bool,
}

/// What:
///  Everything the section is written from.
///  `Vec<String>` is an owned list of owned text.
/// Why:
///   One value holds the host facts, so the wording is a pure function of it.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type FilesystemFacts = { root: string; kind: FilesystemKind; rootIsSubvolume: boolean; mount?: MountSummary; rootSource?: string; ostreeBooted: boolean; kernelRootflags: string[] };
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct FilesystemFacts {
    /// The repository's main checkout.
    pub root: PathBuf,
    /// The filesystem kind holding it.
    pub kind: FilesystemKind,
    /// Whether the checkout is a subvolume root (inode 256 on btrfs).
    pub root_is_subvolume: bool,
    /// The mount holding it, when the mount table could be read.
    pub mount: Option<MountSummary>,
    /// The source of the filesystem the kernel command line's `rootflags=` configures: the mount at `/sysroot` on an
    /// ostree host, else the mount at `/`.
    pub root_source: Option<String>,
    /// Whether the host is an ostree or bootc deployment (`/run/ostree-booted` exists).
    pub ostree_booted: bool,
    /// The values of every `rootflags=` word on the running kernel command line, as written there (quotes included).
    pub kernel_rootflags: Vec<String>,
}

/// What:
///  The words of a kernel command line, split as the kernel splits it: at whitespace outside double quotes.
/// Why:
///   A double quote toggles quoting wherever it stands in a word, so `rootflags="subvol=@my root"` is one word; the
///  kernel's `next_arg` (`lib/cmdline.c` and `kernel/params.c`) counts quotes the same way and strips them afterwards.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// const words = (cmdline: string) => splitOutsideQuotes(cmdline, /\s/);
/// ```
fn command_line_words(command_line: &str) -> Vec<&str> {
    let mut words: Vec<&str> = Vec::new();
    let mut start: Option<usize> = None;
    let mut in_quote: bool = false;
    for (index, character) in command_line.char_indices() {
        if character.is_whitespace() && !in_quote {
            if let Some(began) = start.take() {
                words.push(&command_line[began..index]);
            }
            continue;
        }
        if start.is_none() {
            start = Some(index);
        }
        if character == '"' {
            in_quote = !in_quote;
        }
    }
    if let Some(began) = start {
        words.push(&command_line[began..]);
    }
    return words;
}

/// What:
///  A kernel argument value without the quote that opens it and the quote that closes it.
/// Why:
///   The kernel strips a leading quote from a value and a trailing one when the value had a leading one; quotes inside a
///  value stay (they only toggled the splitting). The option check reads this form.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// const kernelValue = (raw: string) => raw.startsWith('"') ? raw.slice(1).replace(/"$/, '') : raw;
/// ```
pub fn kernel_value(raw: &str) -> String {
    let Some(rest) = raw.strip_prefix('"') else { return raw.to_string() };
    return rest.strip_suffix('"').unwrap_or(rest).to_string();
}

/// What:
///  The values of the `rootflags=` words of a kernel command line, as written there (a quoted value keeps its quotes).
/// Why:
///   The persistent command on an ostree host replaces that exact value, so it is read from the running system and
///  never guessed. The value is everything after the first `=`, because the value itself contains `=`. A word quoted as
///  a whole (`"rootflags=a b"`) is unwrapped first, as the kernel does.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// const rootflags = (cmdline: string) => words(cmdline).map(unwrap).filter((w) => w.startsWith('rootflags=')).map((w) => w.slice(10));
/// ```
pub fn parse_rootflags(command_line: &str) -> Vec<String> {
    return command_line_words(command_line)
        .into_iter()
        .filter_map(|word: &str| {
            let unwrapped: &str = word.strip_prefix('"').and_then(|inner: &str| { return inner.strip_suffix('"'); }).filter(|inner: &&str| { return !inner.is_empty(); }).unwrap_or(word);
            return unwrapped.strip_prefix("rootflags=");
        })
        .map(str::to_string)
        .collect();
}

/// What:
///  Read the facts for a checkout from the running system.
/// Why:
///   A fact that cannot be read becomes the plain answer (`None`, empty list, `false`), and the wording states less.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// const facts = await gatherFacts(root);
/// ```
pub fn gather_facts(root: &Path) -> Option<FilesystemFacts> {
    let kind: FilesystemKind = filesystem_kind(root).ok()?;
    let root_is_subvolume: bool = kind == FilesystemKind::Btrfs && is_subvolume_root(root).unwrap_or(false);
    let mount: Option<MountSummary> = read_mount_facts(root).ok().flatten().map(|facts| {
        return MountSummary { has_removal_option: facts.has_option(REMOVAL_OPTION), source: facts.source.clone(), mount_point: facts.mount_point };
    });
    let ostree_booted: bool = Path::new(OSTREE_BOOTED_PATH).exists();
    let root_source: Option<String> = read_mount_facts(Path::new(if ostree_booted { SYSROOT_PATH } else { "/" })).ok().flatten().map(|facts| { return facts.source; });
    let command_line: String = std::fs::read_to_string(CMDLINE_PATH).unwrap_or_default();
    return Some(FilesystemFacts {
        root: root.to_path_buf(),
        kind,
        root_is_subvolume,
        mount,
        root_source,
        ostree_booted,
        kernel_rootflags: parse_rootflags(command_line.as_str()),
    });
}

/// The wording for a filesystem that is neither btrfs nor overlayfs.
fn other_lines(facts: &FilesystemFacts) -> Vec<String> {
    return vec![format!(
        "{} {} is on a filesystem other than btrfs or overlayfs. `git worktree add` uses Git's own checkout there, and no faster method applies.",
        SECTION_MARKER,
        facts.root.display()
    )];
}

/// The wording for overlayfs.
fn overlay_lines(facts: &FilesystemFacts) -> Vec<String> {
    return vec![
        format!("{} {} is on overlayfs.", SECTION_MARKER, facts.root.display()),
        String::from("  Cloning a file's data into another file inside the same overlay works, so the wrapper's copy of ignored files uses clones there; a snapshot does not apply, because snapshots need a btrfs subvolume and the btrfs under an overlay cannot be addressed from inside it."),
        String::from("  `git worktree add` uses Git's own checkout, which was several times slower on an overlay than on btrfs in one measurement (doc/planning/cli-git-btrfs-worktree.md, section Overlayfs)."),
    ];
}

/// The value with the option added: inside the closing quote of a quoted value, at the end of any other.
fn with_removal_option(raw: &str) -> String {
    if raw.starts_with('"') && raw.len() > 1 && let Some(inner) = raw.strip_suffix('"') {
        return format!("{inner},{REMOVAL_OPTION}\"");
    }
    return format!("{raw},{REMOVAL_OPTION}");
}

/// The persistent way to set the option on an ostree host, for the filesystem the kernel command line configures.
fn kernel_argument_lines(facts: &FilesystemFacts) -> Vec<String> {
    return match facts.kernel_rootflags.as_slice() {
        [old] if kernel_value(old).split(',').any(|option: &str| { return option == REMOVAL_OPTION; }) => vec![format!(
            "  Kept across boots: the running kernel command line already lists `{REMOVAL_OPTION}` in `rootflags=`, so a mount that lacks it was made before that; reboot, and compare with the output of `rpm-ostree kargs`."
        )],
        [old] => vec![
            String::from("  Kept across boots on this ostree host, then reboot (the value is the `rootflags=` of the running kernel command line; compare it with the output of `rpm-ostree kargs` before running):"),
            format!(
                "    sudo rpm-ostree kargs {} {}",
                shell_quote(format!("--delete=rootflags={old}").as_bytes()),
                shell_quote(format!("--append=rootflags={}", with_removal_option(old)).as_bytes())
            ),
            String::from("  Use delete and append, not `--replace`: the value contains `=`, and libostree splits each argument at the first `=`, so `--replace=rootflags=...` reads the old value as only the part before the next `=`."),
        ],
        [] => vec![String::from("  Kept across boots: this ostree host's kernel command line has no `rootflags=` word, so the mount options come from somewhere else (for example `/etc/fstab`); add the option there.")],
        _ => vec![String::from("  Kept across boots: this host's kernel command line has several `rootflags=` words, so no single command is printed; edit them with `rpm-ostree kargs --editor`.")],
    };
}

/// The commands that make the removal option active, for the host the facts describe.
fn removal_option_lines(facts: &FilesystemFacts, mount: &MountSummary) -> Vec<String> {
    let mount_point: &Path = mount.mount_point.as_path();
    let mut lines: Vec<String> = vec![
        format!("  The mount {} lacks `{REMOVAL_OPTION}`. Without it, deleting a worktree that is a subvolume works but unlinks its files one by one; with it, one call deletes the subvolume.", mount_point.display()),
        format!("  Active until the next boot or unmount: sudo mount --options remount,{REMOVAL_OPTION} {}", shell_quote(mount_point.as_os_str().as_bytes())),
    ];
    let on_root_filesystem: bool = facts.root_source.as_deref() == Some(mount.source.as_str());
    if facts.ostree_booted && on_root_filesystem {
        lines.extend(kernel_argument_lines(facts));
    } else if facts.ostree_booted {
        lines.push(format!("  Kept across boots: {} is not the root filesystem, so the kernel command line's `rootflags=` does not apply to it; add the option to its `/etc/fstab` entry or its systemd mount unit, then reboot.", mount_point.display()));
    } else {
        lines.push(format!("  Kept across boots on a conventional host: add `{REMOVAL_OPTION}` to the options of this filesystem's entry in /etc/fstab (every btrfs entry that shares its filesystem), then reboot."));
    }
    return lines;
}

/// The wording for btrfs.
fn btrfs_lines(facts: &FilesystemFacts) -> Vec<String> {
    let mut lines: Vec<String> = Vec::new();
    if facts.root_is_subvolume {
        lines.push(format!("{} {} is a btrfs subvolume.", SECTION_MARKER, facts.root.display()));
    } else {
        lines.push(format!("{} {} is on btrfs but is an ordinary directory, not a subvolume.", SECTION_MARKER, facts.root.display()));
        lines.push(String::from("  Making it a subvolume can help with performance: worktrees can then be made from btrfs snapshots, which took a median of 0.35 s to 1.09 s in the design measurements, against 2.1 s to 2.7 s for Git's checkout and 28.35 s with an ignored tree of 72 thousand entries, and share every data block with their source (doc/planning/cli-git-btrfs-worktree.md, section Measurements)."));
        lines.push(String::from("  This version of the wrapper does not create worktrees from snapshots yet; `git worktree add` still uses Git's checkout. The conversion keeps the original tree until you delete it."));
        lines.push(String::from("  Stop agent sessions and editors that have their working directory inside the checkout first, then:"));
        lines.push(String::from("    git cli-git migrate-to-subvolume --dry-run"));
        lines.push(String::from("    git cli-git migrate-to-subvolume"));
    }
    match &facts.mount {
        Some(mount) if mount.has_removal_option => {
            lines.push(format!("  The mount {} has `{REMOVAL_OPTION}`: a subvolume worktree is deleted in one call.", mount.mount_point.display()));
        }
        Some(mount) => lines.extend(removal_option_lines(facts, mount)),
        None => lines.push(String::from("  The mount table could not be read, so `user_subvol_rm_allowed` was not checked.")),
    }
    return lines;
}

/// What:
///  The section text for the facts: lines ending in a line feed, the first beginning with `SECTION_MARKER`.
/// Why:
///   Pure wording, so every case is tested without the host.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// const text = renderSection(facts);
/// ```
pub fn render_section(facts: &FilesystemFacts) -> String {
    let lines: Vec<String> = match facts.kind {
        FilesystemKind::Btrfs => btrfs_lines(facts),
        FilesystemKind::Overlayfs => overlay_lines(facts),
        FilesystemKind::Other => other_lines(facts),
    };
    let mut text: String = lines.join("\n");
    text.push('\n');
    return text;
}

/// What:
///  The section for the repository whose common Git directory is given, read from the running system; empty when that
///  directory is not a `.git` directory (a bare repository has no main checkout) or its filesystem cannot be identified.
/// Why:
///   This is what the command appends to the doctor's standard error. Git chose the common directory, so a worktree,
///  `-C` and `--git-dir` all lead to the right main checkout without a second guess. A repository the command cannot
///  place adds no line, because a guess about the wrong directory would mislead.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// const section = hostSection(commonGitDirectory);
/// ```
pub fn host_section(common_directory: &Path) -> String {
    if common_directory.file_name().is_none_or(|name: &std::ffi::OsStr| { return name != ".git"; }) {
        return String::new();
    }
    let Some(root) = common_directory.parent() else { return String::new() };
    return gather_facts(root).map(|facts: FilesystemFacts| { return render_section(&facts); }).unwrap_or_default();
}

/// Filesystem section controls stay out of the release executable.
#[cfg(test)]
#[path = "doctor_filesystem_tests.rs"]
mod tests;