On 2025-08-23 11:27, Phillip Lougher wrote:
Yeah let's take the attitude everyone writes well written programs, and if they
don't it's their fault when they unexpectedly break in production. In reality
a lot of code in embedded Linux systems is dreadful, written by inexperienced
programmers.
Inexperienced programmers don't use SEEK_HOLE or SEEK_DATA.
Several commonly-used programs would benefit from proper support for
SEEK_HOLE and SEEK_DATA. What programs would be hurt? If nobody knows of
such programs, we should be skeptical of the argument that support would
be dangerous. To be honest I can't think of why it would hurt in
practical programs.
Anyway, my email was pointing out that the SEEK_HOLE behaviour being
complained about is the default Linux VFS behaviour. So this isn't
about Squashfs.
Yes it is. The default behavior is appropriate for simple file systems
that lack extents. However, Squashfs is not such a file system. If
Squashfs has extents but does not expose them to user code, user code
can be waaaaaayy less efficient.
And this isn't merely an efficiency issue. It can be a security issue,
as sparse files can be used for denial-of-service attacks. I assume
efficiency and security are of concern to Squashfs users, which is why I
press this point.
