What is the Btrfs extended attribute 'm'?
I recently found one of my Virtual Machine images with the extended attribute 'm'. I tried to look it up, but I found no information. Is this an undocumented extended attribute?
$ lsattr usb2ubuntu.btrfs.img*
---------------------m usb2ubuntu.btrfs.img
---------------------- usb2ubuntu.btrfs.img.210810_15:02:49.bak
Notice the attribute doesn't exist on the backup file.
Solution 1:
The chattr manpage says:
m A file with the 'm' attribute is excluded from compression
on file systems that support per-file compression.