ADDITIONAL SYSTEM INFORMATION :
Ubuntu 22.04
Java 20 EA

A DESCRIPTION OF THE PROBLEM :
The error message thrown here, says "Current location of the bytebuffer ... is not a multiple of the block size"

https://github.com/openjdk/jdk/blob/861cc671e2e4904d94f50710be99a511e2f9bb68/src/java.base/share/classes/sun/nio/ch/Util.java#L505-L514

If you open a FileChannel in O_DIRECT mode and use ByteBuffers with it, an unaligned read gives a misleading error message:

Exception in thread "main" java.io.IOException: Current location of the bytebuffer (0) is not a multiple of the block size (512)
at java.base/sun.nio.ch.Util.checkBufferPositionAligned(Util.java:513)

This isn't true (you can do two reads, both with the buffer at location = 0, and the first might work while the second can fail)

It should more accurately say "Current location ... is not a multiple of the block size, or is not aligned"
and include the output of "bb.alignmentOffset(pos, alignment)" IMO