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

[Sam Li]

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.

> 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;
> > +
> > +    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.

>
> > +    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