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Re: [PATCH v3] block/gluster: correctly set max_pdiscard

From: Stefano Garzarella
Subject: Re: [PATCH v3] block/gluster: correctly set max_pdiscard
Date: Wed, 25 May 2022 11:12:36 +0200

On Fri, May 20, 2022 at 09:59:22AM +0200, Fabian Ebner wrote:
On 64-bit platforms, assigning SIZE_MAX to the int64_t max_pdiscard
results in a negative value, and the following assertion would trigger
down the line (it's not the same max_pdiscard, but computed from the
other one):
qemu-system-x86_64: ../block/io.c:3166: bdrv_co_pdiscard: Assertion
`max_pdiscard >= bs->bl.request_alignment' failed.

On 32-bit platforms, it's fine to keep using SIZE_MAX.

The assertion in qemu_gluster_co_pdiscard() is checking that the value
of 'bytes' can safely be passed to glfs_discard_async(), which takes a
size_t for the argument in question, so it is kept as is. And since
max_pdiscard is still <= SIZE_MAX, relying on max_pdiscard is still

Fixes: 0c8022876f ("block: use int64_t instead of int in driver discard 
Cc: qemu-stable@nongnu.org
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>

v2 -> v3:
   * Keep assertion in qemu_gluster_co_pdiscard() as is.
   * Improve commit message.

v1 -> v2:
   * Use an expression that works for both 64-bit and 32-bit platforms.

block/gluster.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

diff --git a/block/gluster.c b/block/gluster.c
index 398976bc66..b60213ab80 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);

static int qemu_gluster_reopen_prepare(BDRVReopenState *state,

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