On 03/06/21 19:33, Eric Blake wrote:
+/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero
*/
+uint64_t blk_get_max_hw_transfer(BlockBackend *blk)
+{
+ BlockDriverState *bs = blk_bs(blk);
+ uint64_t max = INT_MAX;
This is an unaligned value; should we instead round it down to the
request_alignment granularity?
See below...
+++ b/include/block/block_int.h
@@ -695,6 +695,13 @@ typedef struct BlockLimits {
* clamped down. */
uint32_t max_transfer;
+ /* Maximal hardware transfer length in bytes. Applies whenever
Leading /* on its own line, per our style.
The whole file still uses this style, I can change it if desired or do
it later for the whole file or even the whole block subsystem.
+ * transfers to the device bypass the kernel I/O scheduler, for
+ * example with SG_IO. If larger than max_transfer or if zero,
+ * blk_get_max_hw_transfer will fall back to max_transfer.
+ */
Should we mandate any additional requirements on this value such as
multiple of request_alignment or even power-of-2?
Certainly not power of 2. Multiple of request_alignment probably makes
sense, but max_transfer doesn't have that limit.
Paolo
+ uint64_t max_hw_transfer;
+
/* memory alignment, in bytes so that no bounce buffer is needed */
size_t min_mem_alignment;
