fix(cpio): correct dev_t -> rmajor/rminor mapping

dev_t -> major/minor number mapping is more complicated than the incorrect major=(dev_t >> 8) minor=(dev_t & 0xff) mapping that we currently perform. Fix mapping to match Linux / glibc behaviour. Fixes: #1695 Reported-by: Ethan Wu <[email protected]> Signed-off-by: David Disseldorp <[email protected]>
dracutdevs · Feb 17, 2022 · acc629a · acc629a
1 parent 8bd7ddf
commit acc629a
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/src/dracut-cpio/src/main.rs b/src/dracut-cpio/src/main.rs
@@ -361,9 +361,12 @@ fn archive_path<W: Seek + Write>(
  // no zero terminator for symlink target path
  }
 
+ // Linux kernel uses 32-bit dev_t, encoded as mmmM MMmm. glibc uses 64-bit
+ // MMMM Mmmm mmmM MMmm, which is compatible with the former.
  if ftype.is_block_device() || ftype.is_char_device() {
- rmajor = (md.rdev() >> 8) as u32;
- rminor = (md.rdev() & 0xff) as u32;
+ let rd = md.rdev();
+ rmajor = (((rd >> 32) & 0xfffff000) | ((rd >> 8) & 0x00000fff)) as u32;
+ rminor = (((rd >> 12) & 0xffffff00) | (rd & 0x000000ff)) as u32;
  }
 
  if ftype.is_file() {