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Re: [PATCH 04/17] block/nvme: Be explicit we share NvmeIdCtrl / NvmeIdNs
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH 04/17] block/nvme: Be explicit we share NvmeIdCtrl / NvmeIdNs structures |
Date: |
Fri, 26 Jun 2020 14:45:45 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 |
On 6/26/20 1:19 PM, Stefan Hajnoczi wrote:
> On Thu, Jun 25, 2020 at 08:48:25PM +0200, Philippe Mathieu-Daudé wrote:
>> We allocate an unique chunk of memory then use it for two
>> different structures. Introduce the 'idsz_max' variable to
>> hold the maximum size, to make it clearer the size is enough
>> to hold the two structures.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>> FIXME: reword with something that makes more sense...
>> ---
>> block/nvme.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/nvme.c b/block/nvme.c
>> index 71f8cf27a8..ffda804a8e 100644
>> --- a/block/nvme.c
>> +++ b/block/nvme.c
>> @@ -438,6 +438,7 @@ static void nvme_identify(BlockDriverState *bs, int
>> namespace, Error **errp)
>> BDRVNVMeState *s = bs->opaque;
>> NvmeIdCtrl *idctrl;
>> NvmeIdNs *idns;
>> + size_t idsz_max;
>> NvmeLBAF *lbaf;
>> uint8_t *resp;
>> uint16_t oncs;
>> @@ -448,14 +449,15 @@ static void nvme_identify(BlockDriverState *bs, int
>> namespace, Error **errp)
>> .cdw10 = cpu_to_le32(0x1),
>> };
>>
>> - resp = qemu_try_blockalign0(bs, sizeof(NvmeIdCtrl));
>> + idsz_max = MAX_CONST(sizeof(NvmeIdCtrl), sizeof(NvmeIdNs));
>> + resp = qemu_try_blockalign0(bs, idsz_max);
>> if (!resp) {
>> error_setg(errp, "Cannot allocate buffer for identify response");
>> goto out;
>> }
>> idctrl = (NvmeIdCtrl *)resp;
>> idns = (NvmeIdNs *)resp;
>> - r = qemu_vfio_dma_map(s->vfio, resp, sizeof(NvmeIdCtrl), true, &iova);
>> + r = qemu_vfio_dma_map(s->vfio, resp, idsz_max, true, &iova);
>
> _nvme_check_size() has compile-time asserts that check
> sizeof(NvmeIdCtrl) == sizeof(NvmeIdNs) == 4096.
>
> I suggest the following cleanup:
>
> union {
> NvmeIdCtrl ctrl;
> NvmeIdNs ns;
> } *id;
> ...
> id = qemu_try_blockalign0(bs, sizeof(*id));
> ...
> r = qemu_vfio_dma_map(s->vfio, resp, sizeof(*id), true, &iova);
>
> and accesses to idctl are replaced with id->ctrl and idns with id->ns.
>
> This eliminates the casts, makes it clear that this data is overlapping,
> and avoids the need for idsz_max.
Clever idea, thanks!
- Re: [PATCH 01/17] block/nvme: Avoid further processing if trace event not enabled, (continued)
[PATCH 02/17] block/nvme: Let nvme_create_queue_pair() fail gracefully, Philippe Mathieu-Daudé, 2020/06/25
[PATCH 03/17] block/nvme: Define QUEUE_INDEX macros to ease code review, Philippe Mathieu-Daudé, 2020/06/25
[PATCH 05/17] block/nvme: Replace qemu_try_blockalign0 by qemu_try_blockalign/memset, Philippe Mathieu-Daudé, 2020/06/25
[PATCH 04/17] block/nvme: Be explicit we share NvmeIdCtrl / NvmeIdNs structures, Philippe Mathieu-Daudé, 2020/06/25
[PATCH 06/17] block/nvme: Replace qemu_try_blockalign(bs) by qemu_try_memalign(pg_sz), Philippe Mathieu-Daudé, 2020/06/25
[PATCH 07/17] block/nvme: Move code around, Philippe Mathieu-Daudé, 2020/06/25
[PATCH 08/17] block/nvme: Use correct type void*, Philippe Mathieu-Daudé, 2020/06/25
[PATCH 09/17] block/nvme: Remove unused argument from nvme_free_queue_pair(), Philippe Mathieu-Daudé, 2020/06/25