On 15/04/2025 18:34, Darrick J. Wong wrote:
+ /*
+ * Spanning multiple extents would mean that multiple BIOs would be
+ * issued, and so would lose atomicity required for REQ_ATOMIC-based
+ * atomics.
+ */
+ if (!imap_spans_range(imap, offset_fsb, end_fsb))
+ return false;
+
+ /*
+ * The ->iomap_begin caller should ensure this, but check anyway.
+ */
+ if (len > xfs_inode_buftarg(ip)->bt_bdev_awu_max)
+ return false;
This needs to check len against bt_bdev_awu_min so that we don't submit
too-short atomic writes to the hardware.
Right, let me check this.
I think that we should only support sane HW which can write 1x FS block
or more.
Let's say that the hardware
minimum is 32k and the fsblock size is 4k. XFS can perform an out of
place write for 4k-16k writes, but right now we'll just throw invalid
commands at the bdev, and it'll return EINVAL.
/me wonders if statx should grow a atomic_write_unit_min_opt field
too, unless everyone in block layer land is convinced that awu_min will
always match lbasize? (I probably missed that conversation)
Nothing states that it should (match lbasize), but again HW which can
only write >1 FS block is something which I don't want to support (yet).
Thanks,
John
