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

[Sam Li]

Damien Le Moal <damien.lemoal@opensource.wdc.com> 于2022年6月28日周二 17:05写道：
>
> 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.

Can I just remove len argument and blk_check_byte_request() if it's not used?

>
> >
> >> 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 ?

I am not sure it is the case. Can you show me some way to find the problem?

Thanks for reviewing!


>
> >
> >>
> >>> +    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