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

[Stefano Garzarella]

On Thu, May 12, 2022 at 05:44:13PM +0200, Stefano Garzarella wrote:
>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?

Okay, I just saw Eric's answer to v1 and I think this is right.

Please explain it in the commit message and also the initial problem 
that is SIZE_MAX on a 64-bit platform is a negative number for int64_t, 
so the assert fails.

Thanks,
Stefano

>(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