iolog: drop struct io_sample_offset

iolog: drop struct io_sample_offset

Fio uses the struct io_sample to log attributes of each IO. When the
log_offset option is set, fio uses the struct io_sample_offset instead
which has the additional field dedicated to the offset data. Fio chooses
one of these two structs by the log_offset option to minimize memory
usage for IO sampling. However, the dedicated struct io_sample_offset is
not flexible and makes it difficult to add new sampling items.

To allow adding new sampling items, drop the struct io_sample_offset.
Instead, introduce the variable length array "uint64_t aux[]" at the
end of the struct io_sample which holds any auxiliary sampling data.
At this moment, it holds only one item "offset" as the first array
element. The following patch will add a new item.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20240829085826.999859-5-shinichiro.kawasaki@wdc.com
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>