Subject: bug#79267: cp --sparse=auto heuristic fails on a squashfs mounted drive.

From: Phillip Lougher <[email-masked]>
Date: Sat, 23 Aug 2025 05:26:26 +0100

Padraig Brady wrote:

 > with --sparse=always. squashfs is giving the wrong info here after 
all, right?

No Squashfs is not giving the wrong information here.

Support for SEEK_HOLE/SEEK_DATA is not mandated, and no Linux filesystem 
is required to support it.

What you are seeing here is the default Linux VFS behaviour.

See 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/read_write.c#n102

Phillip

---
Squashfs author and maintainer