On Fri, Jul 24, 2020 at 09:19:20PM +0530, Kanchan Joshi wrote:

For zoned block device, opt in for zone-append by setting
FMODE_ZONE_APPEND during open. Make direct IO submission path use
IOCB_ZONE_APPEND to send bio with append op. Make direct IO completion
return written-offset, in bytes, to upper layer via ret2 of
kiocb->ki_complete interface.
Write with the flag IOCB_ZONE_APPEND are ensured not be be short.
Prevent short write and instead return failure if appending write spans
beyond end of device.
Return failure if write is larger than max_append_limit and therefore
requires formation of multiple bios.

We should support reporting the append offset for all block devices
and all file systems support by iomap at least.  There is nothing that
requires actual zone append support here.