O_DIRECT implementation misses statx(STATX_DIOALIGN) extension

[amotin]

To properly use O_DIRECT, applications need to know file system requirements for I/O and buffer alignments. As was mentioned in #16953 (comment), STATX_DIOALIGN extension to statx() (https://man7.org/linux/man-pages/man2/statx.2.html) seems to be the way to do it on Linux since kernel 6.1. Unfortunately it seems zpl_getattr_impl() code around here

zfs/module/os/linux/zfs/zpl_inode.c

Line 486 in 919bc4d

#ifdef STATX_BTIME

does not implement it, while it seems to be an easy change.

[robn]

I've actually been working on it this week. Hoping to post the PR today.