Re: [RFC v3 1/5] block: add block layer APIs resembling Linux ZonedBlockDevice ioctls.

[Damien Le Moal]

On 6/28/22 17:05, Sam Li wrote:
> Stefan Hajnoczi <stefanha@redhat.com> 于2022年6月28日周二 14:52写道：
>>
>> On Mon, Jun 27, 2022 at 08:19:13AM +0800, Sam Li wrote:
>>> diff --git a/block/block-backend.c b/block/block-backend.c
>>> index e0e1aff4b1..786f964d02 100644
>>> --- a/block/block-backend.c
>>> +++ b/block/block-backend.c
>>> @@ -1810,6 +1810,62 @@ int blk_flush(BlockBackend *blk)
>>>      return ret;
>>>  }
>>>
>>> +/*
>>> + * Return zone_report from BlockDriver. Offset can be any number within
>>> + * the zone size. No alignment for offset and len.
>>
>> What is the purpose of len? Is it the maximum number of zones to return
>> in nr_zones[]?
> 
> len is actually not used in bdrv_co_zone_report. It is needed by
> blk_check_byte_request.

There is no IO buffer being passed. Only an array of zone descriptors and
an in-out number of zones. len is definitely not needed. Not sure what
blk_check_byte_request() is intended to check though.

> 
>> How does the caller know how many zones were returned?
> 
> nr_zones represents IN maximum and OUT actual. The caller will know by
> nr_zones which is changed in bdrv_co_zone_report. I'll add it in the
> comments.
> 
>>
>>> + */
>>> +int coroutine_fn blk_co_zone_report(BlockBackend *blk, int64_t offset,
>>> +                       int64_t len, int64_t *nr_zones,
>>> +                       BlockZoneDescriptor *zones)
>>> +{
>>> +    int ret;
>>> +    BlockDriverState *bs;
>>> +    IO_CODE();
>>> +
>>> +    blk_inc_in_flight(blk); /* increase before waiting */
>>> +    blk_wait_while_drained(blk);
>>> +    bs = blk_bs(blk);
>>> +
>>> +    ret = blk_check_byte_request(blk, offset, len);
>>> +    if (ret < 0) {
>>> +        return ret;
>>> +    }
>>> +
>>> +    bdrv_inc_in_flight(bs);
>>
>> The bdrv_inc/dec_in_flight() call should be inside
>> bdrv_co_zone_report(). See bdrv_co_ioctl() for an example.
>>
>>> +    ret = bdrv_co_zone_report(blk->root->bs, offset, len,
>>> +                              nr_zones, zones);
>>> +    bdrv_dec_in_flight(bs);
>>> +    blk_dec_in_flight(blk);
>>> +    return ret;
>>> +}
>>> +
>>> +/*
>>> + * Return zone_mgmt from BlockDriver.
>>
>> Maybe this should be:
>>
>>   Send a zone management command.
> 
> Yes, it's more accurate.
> 
>>
>>> @@ -216,6 +217,11 @@ typedef struct RawPosixAIOData {
>>>              PreallocMode prealloc;
>>>              Error **errp;
>>>          } truncate;
>>> +        struct {
>>> +            int64_t *nr_zones;
>>> +            BlockZoneDescriptor *zones;
>>> +        } zone_report;
>>> +        zone_op op;
>>
>> It's cleaner to put op inside a struct zone_mgmt so its purpose is
>> self-explanatory:
>>
>>   struct {
>>       zone_op op;
>>   } zone_mgmt;
>>
>>> +static int handle_aiocb_zone_report(void *opaque) {
>>> +    RawPosixAIOData *aiocb = opaque;
>>> +    int fd = aiocb->aio_fildes;
>>> +    int64_t *nr_zones = aiocb->zone_report.nr_zones;
>>> +    BlockZoneDescriptor *zones = aiocb->zone_report.zones;
>>> +    int64_t offset = aiocb->aio_offset;
>>> +    int64_t len = aiocb->aio_nbytes;

Since you have the zone array and number of zones (size of that array) I
really do not see why you need len.

>>> +
>>> +    struct blk_zone *blkz;
>>> +    int64_t rep_size, nrz;
>>> +    int ret, n = 0, i = 0;
>>> +
>>> +    nrz = *nr_zones;
>>> +    if (len == -1) {
>>> +        return -errno;
>>
>> Where is errno set? Should this be an errno constant instead like
>> -EINVAL?
> 
> That's right! Noted.
> 
>>
>>> +    }
>>> +    rep_size = sizeof(struct blk_zone_report) + nrz * sizeof(struct 
>>> blk_zone);
>>> +    g_autofree struct blk_zone_report *rep = g_new(struct blk_zone_report, 
>>> nrz);
>>
>> g_new() looks incorrect. There should be 1 struct blk_zone_report
>> followed by nrz struct blk_zone structs. Please use g_malloc(rep_size)
>> instead.
> 
> Yes! However, it still has a memory leak error when using g_autofree
> && g_malloc.

That may be because you are changing the value of the rep pointer while
parsing the report ?

> 
>>
>>> +    offset = offset / 512; /* get the unit of the start sector: sector 
>>> size is 512 bytes. */
>>> +    printf("start to report zone with offset: 0x%lx\n", offset);
>>> +
>>> +    blkz = (struct blk_zone *)(rep + 1);
>>> +    while (n < nrz) {
>>> +        memset(rep, 0, rep_size);
>>> +        rep->sector = offset;
>>> +        rep->nr_zones = nrz;
>>
>> What prevents zones[] overflowing? nrz isn't being reduced in the loop,
>> so maybe the rep->nr_zones return value will eventually exceed the
>> number of elements still available in zones[n..]?
> 
> I suppose the number of zones[] is restricted in the subsequent for
> loop where zones[] copy one zone at a time as n increases. Even if
> rep->zones exceeds the available room in zones[], the extra zone will
> not be copied.
> 
>>
>>> +static int handle_aiocb_zone_mgmt(void *opaque) {
>>> +    RawPosixAIOData *aiocb = opaque;
>>> +    int fd = aiocb->aio_fildes;
>>> +    int64_t offset = aiocb->aio_offset;
>>> +    int64_t len = aiocb->aio_nbytes;
>>> +    zone_op op = aiocb->op;
>>> +
>>> +    struct blk_zone_range range;
>>> +    const char *ioctl_name;
>>> +    unsigned long ioctl_op;
>>> +    int64_t zone_size;
>>> +    int64_t zone_size_mask;
>>> +    int ret;
>>> +
>>> +    ret = ioctl(fd, BLKGETZONESZ, &zone_size);
>>
>> Can this value be stored in bs (maybe in BlockLimits) to avoid calling
>> ioctl(BLKGETZONESZ) each time?
> 
> Yes, zone_size is in the zbd_dev field. I'll update BlockLimits after
> I think through the configurations. In addition, it's a temporary
> approach. It is substituted by get_sysfs_long_val now.
> 
>>
>>> +    if (ret) {
>>> +        return -1;
>>
>> The return value should be a negative errno. -1 is -EPERM but it's
>> probably not that error code you wanted. This should be:
>>
>>   return -errno;
>>
>>> +    }
>>> +
>>> +    zone_size_mask = zone_size - 1;
>>> +    if (offset & zone_size_mask) {
>>> +        error_report("offset is not the start of a zone");
>>> +        return -1;
>>
>> return -EINVAL;
>>
>>> +    }
>>> +
>>> +    if (len & zone_size_mask) {
>>> +        error_report("len is not aligned to zones");
>>> +        return -1;
>>
>> return -EINVAL;
>>
>>> +static int coroutine_fn raw_co_zone_report(BlockDriverState *bs, int64_t 
>>> offset,
>>> +        int64_t len, int64_t *nr_zones,
>>> +        BlockZoneDescriptor *zones) {
>>> +    BDRVRawState *s = bs->opaque;
>>> +    RawPosixAIOData acb;
>>> +
>>> +    acb = (RawPosixAIOData) {
>>> +        .bs         = bs,
>>> +        .aio_fildes = s->fd,
>>> +        .aio_type   = QEMU_AIO_IOCTL,
>>> +        .aio_offset = offset,
>>> +        .aio_nbytes = len,
>>> +        .zone_report    = {
>>> +                .nr_zones       = nr_zones,
>>> +                .zones          = zones,
>>> +                },
>>
>> Indentation is off here. Please use 4-space indentation.
> Noted!
> 
> Thanks for reviewing!
> 
> Sam


-- 
Damien Le Moal
Western Digital Research