file-posix: fix max_iov for /dev/sg devices

Even though it was only called for devices that have bs->sg set (which
must be character devices), sg_get_max_segments looked at /sys/dev/block
which only works for block devices.

On Linux the sg driver has its own way to provide the maximum number of
iovecs in a scatter/gather list, so add support for it.  The block device
path is kept because it will be reinstated in the next patches.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
1 file changed