bugfix: Switch losetup to --direct-io=off by default

When using a loopback device pointing to a file on a 9p filesystem (e.g.
the home mount of a podman machine), using direct-io=on causes the
partitioning via sgdisk to fail. This is a temporary fix until podman
machine switches away from 9p or another fix is found. Direct IO can be
enabled via the BOOTC_DIRECT_IO=on environment variable.

Fixes #485

Signed-off-by: Chris Kyrouac <ckyrouac@redhat.com>

Author: ckyrouac

docs/src/bootc-install.md

@@ -167,6 +167,8 @@ podman run --rm --privileged --pid=host --security-opt label=type:unconfined_t
 
 Notice that we use `--generic-image` for this use case.
 
+Set the environment variable `BOOTC_DIRECT_IO=on` to create the loopback device with direct-io enabled.
+
 ### Using `bootc install to-existing-root`
 
 This is a variant of `install to-filesystem`, which maximizes convenience for using

lib/src/blockdev.rs

@@ -8,6 +8,7 @@ use once_cell::sync::Lazy;
 use regex::Regex;
 use serde::Deserialize;
 use std::collections::HashMap;
+use std::env;
 use std::fs::File;
 use std::os::unix::io::AsRawFd;
 use std::path::Path;
@@ -83,8 +84,24 @@ pub(crate) struct LoopbackDevice {
 impl LoopbackDevice {
     // Create a new loopback block device targeting the provided file path.
     pub(crate) fn new(path: &Path) -> Result<Self> {
+        let direct_io = match env::var("BOOTC_DIRECT_IO") {
+            Ok(val) => {
+                if val == "on" {
+                    "on"
+                } else {
+                    "off"
+                }
+            }
+            Err(_e) => "off",
+        };
+
         let dev = Task::new("losetup", "losetup")
-            .args(["--show", "--direct-io=on", "-P", "--find"])
+            .args([
+                "--show",
+                format!("--direct-io={direct_io}").as_str(),
+                "-P",
+                "--find",
+            ])
             .arg(path)
             .quiet()
             .read()?;