Re: [Qemu-devel] [PATCH v2 20/20] scsi-disk: correctly implement WRITE SAME

[ronnie sahlberg]

That means the initiator will do the "split into smaller manageable
chunks" for you and you get a 1-to-1 mapping between WS10/16 that the
initiator issues to qemu and the write-same calls that qemu generates.

On Tue, Nov 19, 2013 at 9:23 AM, ronnie sahlberg
<address@hidden> wrote:
> +#define SCSI_WRITE_SAME_MAX         524288
> ...
> +    data->iov.iov_len = MIN(data->nb_sectors * 512, SCSI_WRITE_SAME_MAX);
>
> I don't  think you should just clamp the data to 512k, instead I think
> you should report the 512k max write same size through
> BlockLimitsVPD/MaximumWriteSameLength to the initiator.
> Then instead of clamping the write to MIN()  you return a check
> condition if the initiator sends too much.
>
> On Tue, Nov 19, 2013 at 9:07 AM, Paolo Bonzini <address@hidden> wrote:
>> Fetch the data to be written from the input buffer.  If it is all zeroes,
>> we can use the write_zeroes call (possibly with the new MAY_UNMAP flag).
>> Otherwise, do as many write cycles as needed, writing 512k at a time.
>>
>> Strictly speaking, this is still incorrect because a zero cluster should
>> only be written if the MAY_UNMAP flag is set.  But this is a bug in qcow2
>> and the other formats, not in the SCSI code.
>>
>> Signed-off-by: Paolo Bonzini <address@hidden>
>> ---
>>  hw/scsi/scsi-disk.c | 140 
>> +++++++++++++++++++++++++++++++++++++++++++---------
>>  1 file changed, 116 insertions(+), 24 deletions(-)
>>
>> diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
>> index 0640bb0..4cc6a28 100644
>> --- a/hw/scsi/scsi-disk.c
>> +++ b/hw/scsi/scsi-disk.c
>> @@ -41,6 +41,7 @@ do { printf("scsi-disk: " fmt , ## __VA_ARGS__); } while 
>> (0)
>>  #include <scsi/sg.h>
>>  #endif
>>
>> +#define SCSI_WRITE_SAME_MAX         524288
>>  #define SCSI_DMA_BUF_SIZE           131072
>>  #define SCSI_MAX_INQUIRY_LEN        256
>>  #define SCSI_MAX_MODE_LEN           256
>> @@ -634,6 +635,8 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, 
>> uint8_t *outbuf)
>>              buflen = 0x40;
>>              memset(outbuf + 4, 0, buflen - 4);
>>
>> +            outbuf[4] = 0x1; /* wsnz */
>> +
>>              /* optimal transfer length granularity */
>>              outbuf[6] = (min_io_size >> 8) & 0xff;
>>              outbuf[7] = min_io_size & 0xff;
>> @@ -1589,6 +1592,111 @@ invalid_field:
>>      scsi_check_condition(r, SENSE_CODE(INVALID_FIELD));
>>  }
>>
>> +typedef struct WriteSameCBData {
>> +    SCSIDiskReq *r;
>> +    int64_t sector;
>> +    int nb_sectors;
>> +    QEMUIOVector qiov;
>> +    struct iovec iov;
>> +} WriteSameCBData;
>> +
>> +static void scsi_write_same_complete(void *opaque, int ret)
>> +{
>> +    WriteSameCBData *data = opaque;
>> +    SCSIDiskReq *r = data->r;
>> +    SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
>> +
>> +    assert(r->req.aiocb != NULL);
>> +    r->req.aiocb = NULL;
>> +    bdrv_acct_done(s->qdev.conf.bs, &r->acct);
>> +    if (r->req.io_canceled) {
>> +        goto done;
>> +    }
>> +
>> +    if (ret < 0) {
>> +        if (scsi_handle_rw_error(r, -ret)) {
>> +            goto done;
>> +        }
>> +    }
>> +
>> +    data->nb_sectors -= data->iov.iov_len / 512;
>> +    data->sector += data->iov.iov_len / 512;
>> +    data->iov.iov_len = MIN(data->nb_sectors * 512, data->iov.iov_len);
>> +    if (data->iov.iov_len) {
>> +        bdrv_acct_start(s->qdev.conf.bs, &r->acct, data->iov.iov_len, 
>> BDRV_ACCT_WRITE);
>> +        r->req.aiocb = bdrv_aio_writev(s->qdev.conf.bs, data->sector,
>> +                                       &data->qiov, data->iov.iov_len / 512,
>> +                                       scsi_write_same_complete, r);
>> +        return;
>> +    }
>> +
>> +    scsi_req_complete(&r->req, GOOD);
>> +
>> +done:
>> +    if (!r->req.io_canceled) {
>> +        scsi_req_unref(&r->req);
>> +    }
>> +    g_free(data->iov.iov_base);
>> +    g_free(data);
>> +}
>> +
>> +static void scsi_disk_emulate_write_same(SCSIDiskReq *r, uint8_t *inbuf)
>> +{
>> +    SCSIRequest *req = &r->req;
>> +    SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, req->dev);
>> +    uint32_t nb_sectors = scsi_data_cdb_length(r->req.cmd.buf);
>> +    WriteSameCBData *data;
>> +    uint8_t *buf;
>> +    int i;
>> +
>> +    /* Fail if PBDATA=1 or LBDATA=1 or ANCHOR=1.  */
>> +    if (nb_sectors == 0 || (req->cmd.buf[1] & 0x16)) {
>> +        scsi_check_condition(r, SENSE_CODE(INVALID_FIELD));
>> +        return;
>> +    }
>> +
>> +    if (bdrv_is_read_only(s->qdev.conf.bs)) {
>> +        scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
>> +        return;
>> +    }
>> +    if (!check_lba_range(s, r->req.cmd.lba, nb_sectors)) {
>> +        scsi_check_condition(r, SENSE_CODE(LBA_OUT_OF_RANGE));
>> +        return;
>> +    }
>> +
>> +    if (buffer_is_zero(inbuf, s->qdev.blocksize)) {
>> +        int flags = (req->cmd.buf[1] & 0x8) ? BDRV_REQ_MAY_UNMAP : 0;
>> +
>> +        /* The request is used as the AIO opaque value, so add a ref.  */
>> +        scsi_req_ref(&r->req);
>> +        bdrv_acct_start(s->qdev.conf.bs, &r->acct, nb_sectors * 
>> s->qdev.blocksize,
>> +                        BDRV_ACCT_WRITE);
>> +        r->req.aiocb = bdrv_aio_write_zeroes(s->qdev.conf.bs,
>> +                                             r->req.cmd.lba * 
>> (s->qdev.blocksize / 512),
>> +                                             nb_sectors * 
>> (s->qdev.blocksize / 512),
>> +                                             flags, scsi_aio_complete, r);
>> +        return;
>> +    }
>> +
>> +    data = g_new0(WriteSameCBData, 1);
>> +    data->r = r;
>> +    data->sector = r->req.cmd.lba * (s->qdev.blocksize / 512);
>> +    data->nb_sectors = nb_sectors * (s->qdev.blocksize / 512);
>> +    data->iov.iov_len = MIN(data->nb_sectors * 512, SCSI_WRITE_SAME_MAX);
>> +    data->iov.iov_base = buf = g_malloc(data->iov.iov_len);
>> +    qemu_iovec_init_external(&data->qiov, &data->iov, 1);
>> +
>> +    for (i = 0; i < data->iov.iov_len; i += s->qdev.blocksize) {
>> +        memcpy(&buf[i], inbuf, s->qdev.blocksize);
>> +    }
>> +
>> +    scsi_req_ref(&r->req);
>> +    bdrv_acct_start(s->qdev.conf.bs, &r->acct, data->iov.iov_len, 
>> BDRV_ACCT_WRITE);
>> +    r->req.aiocb = bdrv_aio_writev(s->qdev.conf.bs, data->sector,
>> +                                   &data->qiov, data->iov.iov_len / 512,
>> +                                   scsi_write_same_complete, data);
>> +}
>> +
>>  static void scsi_disk_emulate_write_data(SCSIRequest *req)
>>  {
>>      SCSIDiskReq *r = DO_UPCAST(SCSIDiskReq, req, req);
>> @@ -1612,6 +1720,10 @@ static void scsi_disk_emulate_write_data(SCSIRequest 
>> *req)
>>          scsi_disk_emulate_unmap(r, r->iov.iov_base);
>>          break;
>>
>> +    case WRITE_SAME_10:
>> +    case WRITE_SAME_16:
>> +        scsi_disk_emulate_write_same(r, r->iov.iov_base);
>> +        break;
>>      default:
>>          abort();
>>      }
>> @@ -1854,30 +1966,10 @@ static int32_t scsi_disk_emulate_command(SCSIRequest 
>> *req, uint8_t *buf)
>>          break;
>>      case WRITE_SAME_10:
>>      case WRITE_SAME_16:
>> -        nb_sectors = scsi_data_cdb_length(r->req.cmd.buf);
>> -        if (bdrv_is_read_only(s->qdev.conf.bs)) {
>> -            scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
>> -            return 0;
>> -        }
>> -        if (!check_lba_range(s, r->req.cmd.lba, nb_sectors)) {
>> -            goto illegal_lba;
>> -        }
>> -
>> -        /*
>> -         * We only support WRITE SAME with the unmap bit set for now.
>> -         * Reject UNMAP=0 or ANCHOR=1.
>> -         */
>> -        if (!(req->cmd.buf[1] & 0x8) || (req->cmd.buf[1] & 0x10)) {
>> -            goto illegal_request;
>> -        }
>> -
>> -        /* The request is used as the AIO opaque value, so add a ref.  */
>> -        scsi_req_ref(&r->req);
>> -        r->req.aiocb = bdrv_aio_discard(s->qdev.conf.bs,
>> -                                        r->req.cmd.lba * (s->qdev.blocksize 
>> / 512),
>> -                                        nb_sectors * (s->qdev.blocksize / 
>> 512),
>> -                                        scsi_aio_complete, r);
>> -        return 0;
>> +        DPRINTF("WRITE SAME %d (len %lu)\n",
>> +                req->cmd.buf[0] == WRITE_SAME_10 ? 10 : 16,
>> +                (long)r->req.cmd.xfer);
>> +        break;
>>      default:
>>          DPRINTF("Unknown SCSI command (%2.2x)\n", buf[0]);
>>          scsi_check_condition(r, SENSE_CODE(INVALID_OPCODE));
>> --
>> 1.8.4.2
>>
>>