On 7/9/20 8:00 AM, Christoph Hellwig wrote:

On Thu, Jul 09, 2020 at 07:58:04AM -0600, Jens Axboe wrote:

quoted

quoted

We don't actually need any new field at all.  By the time the write
returned ki_pos contains the offset after the write, and the res
argument to ->ki_complete contains the amount of bytes written, which
allow us to trivially derive the starting position.

Then let's just do that instead of jumping through hoops either
justifying growing io_rw/io_kiocb or turning kiocb into a global
completion thing.

Unfortunately that is a totally separate issue - the in-kernel offset
can be trivially calculated.  But we still need to figure out a way to
pass it on to userspace.  The current patchset does that by abusing
the flags, which doesn't really work as the flags are way too small.
So we somewhere need to have an address to do the put_user to.

Right, we're just trading the 'append_offset' for a 'copy_offset_here'
pointer, which are stored in the same spot...

-- 
Jens Axboe