Logical and physical block sizes in QEMU are limited to 32 KiB.

This appears unnecessary tight, and we've seen bigger block sizes handy
at times.

Lift the limitation up to 2 MiB which appears to be good enough for
everybody, and matches the qcow2 cluster size limit.

Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
---
v4 -> v5:
- split out into separate patch [Philippe]
- as this patch has changed significantly lose Eric's r-b

 hw/core/qdev-properties.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
index e7ccd4d276..ecd84262a9 100644
--- a/hw/core/qdev-properties.c
+++ b/hw/core/qdev-properties.c
@@ -784,9 +784,12 @@ const PropertyInfo qdev_prop_size32 = {
 /* lower limit is sector size */
 #define MIN_BLOCK_SIZE          512
 #define MIN_BLOCK_SIZE_STR      stringify(MIN_BLOCK_SIZE)
-/* upper limit is the max power of 2 that fits in uint16_t */
-#define MAX_BLOCK_SIZE          32768
-#define MAX_BLOCK_SIZE_STR      stringify(MAX_BLOCK_SIZE)
+/*
+ * upper limit is arbitrary, 2 MiB looks sufficient for all sensible uses, and
+ * matches qcow2 cluster size limit
+ */
+#define MAX_BLOCK_SIZE          (2 * MiB)
+#define MAX_BLOCK_SIZE_STR      "2 MiB"
 
 static void set_blocksize(Object *obj, Visitor *v, const char *name,
                           void *opaque, Error **errp)
-- 
2.26.2

On 5/27/20 7:45 AM, Roman Kagan wrote:
> Logical and physical block sizes in QEMU are limited to 32 KiB.
> 
> This appears unnecessary tight, and we've seen bigger block sizes handy

unnecessarily

> at times.
> 
> Lift the limitation up to 2 MiB which appears to be good enough for
> everybody, and matches the qcow2 cluster size limit.
> 
> Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
> ---

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org