[PATCH v2] block/gluster: correctly set max_pdiscard

[PATCH v2] block/gluster: correctly set max_pdiscard

[Fabian Ebner]

On 64-bit platforms, SIZE_MAX is too large for max_pdiscard, which is
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@nongnu.org
Signed-off-by: Fabian Ebner <f.ebner@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);
 }
 
 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 */
 
     acb.size = 0;
     acb.ret = 0;
-- 
2.30.2

Re: [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@nongnu.org
>Signed-off-by: Fabian Ebner <f.ebner@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

Re: [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@nongnu.org
>>Signed-off-by: Fabian Ebner <f.ebner@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

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

[Fabian Ebner]

Am 12.05.22 um 18:05 schrieb 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.
>>

Yes, I should've stated that directly.

>>> 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@nongnu.org
>>> Signed-off-by: Fabian Ebner <f.ebner@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.
> 

Sorry for not mentioning the changes from v1.

> 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.
> 

I'll try and improve the commit message for v3.

> 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?
>>

Now I'm thinking that the assert is actually for checking that the value
can be passed to glfs_discard_async(), which takes a size_t for the
argument in question. So maybe it's best to keep assert(bytes <=
SIZE_MAX) as is?

>> Thanks,
>> Stefano
> 
> 
>