Understanding a triggered assertion

[etiennemlb]

What could possibly lead to errno being set to 7 at the following line:

https://github.com/hpc/mpifileutils/blob/0a4c530bca5dc2476418a3833a15ab812d636e78/src/common/mfu_io.c#L1051

This is triggered when making a Tio sized copy of many small files on a recent Luster FS.