Re: [PATCH 1/2] file-posix: Correctly read max_segments of SG nodes

[Paolo Bonzini]

On 17/09/20 15:16, Max Reitz wrote:
> So is this path ever taken, or can we just replace it all with the ioctl?
> 
> (Before 867eccfed84, this function was used for all host devices, which
> might explain why the code even exists.)

Because 867eccfed84 is wrong.  If you use /dev/sda* with SG_IO you do
need to take into account the hardware max segment size/max segment count.

Probably ->sg needs to be set by the front-end, not by the back-end.  An
even better way (but for which I'd leave the task to you and Kevin)
could be to have a new permission BLK_PERM_WRITE_BYPASS and to reduce
the limits to the hardware limits if anybody has requested that
permission.  I tried to implement that a couple years ago but I just
couldn't wrap my mind around the permission code.

Paolo