[GEDI] [PATCH v2] block/gluster: correctly set max_pdiscard

[Stefano Garzarella]

On Thu, May 12, 2022 at 12:30:48PM +0200, Fabian Ebner wrote:
>On 64-bit platforms, SIZE_MAX is too large for max_pdiscard, which is

The main problem is that SIZE_MAX for an int64_t is a negative value.

>int64_t, and the following assertion would be triggered:
>qemu-system-x86_64: ../block/io.c:3166: bdrv_co_pdiscard: Assertion
>`max_pdiscard >= bs->bl.request_alignment' failed.
>
>Fixes: 0c8022876f ("block: use int64_t instead of int in driver discard handlers")
>Cc: qemu-stable at nongnu.org
>Signed-off-by: Fabian Ebner <f.ebner at proxmox.com>
>---
> block/gluster.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/block/gluster.c b/block/gluster.c
>index 398976bc66..f711bf0bd6 100644
>--- a/block/gluster.c
>+++ b/block/gluster.c
>@@ -891,7 +891,7 @@ out:
> static void qemu_gluster_refresh_limits(BlockDriverState *bs, Error **errp)
> {
>     bs->bl.max_transfer = GLUSTER_MAX_TRANSFER;
>-    bs->bl.max_pdiscard = SIZE_MAX;
>+    bs->bl.max_pdiscard = MIN(SIZE_MAX, INT64_MAX);

What would be the problem if we use INT64_MAX?
(I guess the intention of the original patch was to set the maximum 
value in drivers that do not have a specific maximum).

Or we can set to 0, since in block/io.c we have this code:

     max_pdiscard = QEMU_ALIGN_DOWN(MIN_NON_ZERO(bs->bl.max_pdiscard, INT64_MAX),
                                    align);
     assert(max_pdiscard >= bs->bl.request_alignment);

Where `max_pdiscard` is set to INT64_MAX (and aligned) if 
bs->bl.max_pdiscard is 0.

> }
>
> static int qemu_gluster_reopen_prepare(BDRVReopenState *state,
>@@ -1304,7 +1304,7 @@ static coroutine_fn int qemu_gluster_co_pdiscard(BlockDriverState *bs,
>     GlusterAIOCB acb;
>     BDRVGlusterState *s = bs->opaque;
>
>-    assert(bytes <= SIZE_MAX); /* rely on max_pdiscard */
>+    assert(bytes <= MIN(SIZE_MAX, INT64_MAX)); /* rely on max_pdiscard */

Can we use bs->bl.max_pdiscard directly here?

Thanks,
Stefano