Decompression success/failure dependent on PAGE_SIZE?

["Marek Behún" <marek.behun@nic.cz>]

Hello,

so I've been studying the linux btrfs code and have come across this:

in inode.c function uncompress_inline the max_size size variable is set
to min(max_size, PAGE_SIZE) and only max_size of output data are
decompressed.

The code for compression (in lzo.c for example) uses PAGE_SIZEd chunks
to compress an inline extent.

If I understand it correctly, then if the filesystem is created and used
on a computer with PAGE_SIZE for example 16KB, and an extent of size
16KB is compressed to (for example 9KB) and stored as inline extent,
and then the filesystem is mounted on a computer with PAGE_SIZE = 4KB,
reading the extent will result in a failure or incomplete read.

Is this a bug, or is this behaviour a feature?

Thank you.

Marek