install: correctly detect DASDs if they're behind a symlink

src/blockdev.rs

@@ -18,7 +18,7 @@ use nix::{errno::Errno, mount};
 use regex::Regex;
 use std::collections::HashMap;
 use std::convert::TryInto;
-use std::fs::{metadata, read_dir, read_link, read_to_string, remove_dir, File, OpenOptions};
+use std::fs::{metadata, read_dir, read_to_string, remove_dir, File, OpenOptions};
 use std::num::{NonZeroU32, NonZeroU64};
 use std::os::linux::fs::MetadataExt;
 use std::os::raw::c_int;
@@ -30,6 +30,7 @@ use std::thread::sleep;
 use std::time::Duration;
 
 use crate::errors::*;
+use crate::io::resolve_link;
 
 #[derive(Debug)]
 pub struct Disk {
@@ -374,21 +375,17 @@ impl Partition {
         // Now assume a kpartx "partition", where the path is a symlink to
         // an unpartitioned DM device node.
         // /sys/block/dm-1
-        match read_link(Path::new(&self.path)) {
-            Ok(target) => {
-                let devdir = basedir.join(
-                    Path::new(&target)
-                        .file_name()
-                        .chain_err(|| format!("target {} has no filename", self.path))?,
-                );
-                if devdir.exists() {
-                    return Ok(devdir);
-                }
+        let (target, is_link) = resolve_link(&self.path)?;
+        if is_link {
+            let devdir = basedir.join(
+                target
+                    .file_name()
+                    .chain_err(|| format!("target {} has no filename", target.display()))?,
+            );
+            if devdir.exists() {
+                return Ok(devdir);
             }
-            // ignore if not symlink
-            Err(e) if e.kind() == std::io::ErrorKind::InvalidInput => (),
-            Err(e) => return Err(e).chain_err(|| format!("reading link {}", self.path)),
-        };
+        }
 
         // Give up
         bail!(

src/install.rs

@@ -101,7 +101,7 @@ pub fn install(config: &InstallConfig) -> Result<()> {
         }
     }
 
-    if config.device.starts_with("/dev/dasd") {
+    if is_dasd(config)? {
         #[cfg(target_arch = "s390x")]
         s390x::prepare_dasd(&config)?;
     }
@@ -186,7 +186,7 @@ fn write_disk(
     let sector_size = get_sector_size(dest)?;
 
     // copy the image
-    let image_copy = if config.device.starts_with("/dev/dasd") {
+    let image_copy = if is_dasd(config)? {
         #[cfg(target_arch = "s390x")]
         {
             s390x::image_copy_s390x
@@ -485,6 +485,11 @@ fn clear_partition_table(dest: &mut File, table: &mut dyn PartTable) -> Result<(
     Ok(())
 }
 
+fn is_dasd(config: &InstallConfig) -> Result<bool> {
+    let (target, _) = resolve_link(&config.device)?;
+    Ok(target.to_string_lossy().starts_with("/dev/dasd"))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/io.rs

@@ -13,7 +13,9 @@
 // limitations under the License.
 
 use error_chain::bail;
+use std::fs::read_link;
 use std::io::{ErrorKind, Read, Write};
+use std::path::{Path, PathBuf};
 
 use crate::errors::*;
 
@@ -76,3 +78,14 @@ pub fn copy_exactly_n(
     }
     Ok(n)
 }
+
+// If path is a symlink, resolve it and return (target, true)
+// If not, return (path, false)
+pub fn resolve_link<P: AsRef<Path>>(path: P) -> Result<(PathBuf, bool)> {
+    let path = path.as_ref();
+    match read_link(path) {
+        Ok(target) => Ok((target, true)),
+        Err(e) if e.kind() == std::io::ErrorKind::InvalidInput => Ok((path.to_path_buf(), false)),
+        Err(e) => Err(e).chain_err(|| format!("reading link {}", path.display())),
+    }
+}