feature request: "--basedir" alike option to preserve filepaths for sourcefiles

[adabru]

Shamelessly copying the wording from the OP of https://unix.stackexchange.com/q/459284/218172 :

When I create a squashfs image from multiple directories such as:

• /bin/
• /usr/bin/
• /usr/local/bin/
• /some/other/random/folder/
• /another/long/path/

If I use command

mksquashfs /bin /usr/bin /usr/local/bin /some/other/random/folder /another/long/path MyNewImage.squashfs

It gives me an image with these top-level folders:

• bin/
• bin_1/
• bin_2/
• folder/
• path/

I want my image to contain the full paths from the original filesystem:

• bin/
• usr/bin/
• usr/local/bin/
• some/other/random/folder/
• another/long/path/

Currently as a workaround I'm using:

mksquashfs / MyNewImage.squashfs -wildcards -e \
  !(bin|usr|some|another) \
  usr/!(bin|local) \
  usr/local/!(bin) \
  some/!(other) \
  some/other/!(random) \
  some/other/random/!(folder) \
  another/!(long) \
  another/long/!(path)

This is rather cumbersome. A new feature like a basedir option that could be used like --basedir / or --basedir ~ would be very nice, for backing up only a smaller part of the filesystem.

[mars4science]

I find it inconvenient that man page is not up-to-date on that (Linux Mint 21).