Re: [RFC v3 2/5] qemu-io: add zoned block device operations.

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 6/28/22 16:56, Stefan Hajnoczi wrote:
> On Mon, Jun 27, 2022 at 08:19:14AM +0800, Sam Li wrote:
>> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
>> index 2f0d8ac25a..3f2592b9f5 100644
>> --- a/qemu-io-cmds.c
>> +++ b/qemu-io-cmds.c
>> @@ -1706,6 +1706,122 @@ static const cmdinfo_t flush_cmd = {
>>      .oneline    = "flush all in-core file state to disk",
>>  };
>>  
>> +static int zone_report_f(BlockBackend *blk, int argc, char **argv)
>> +{
>> +    int ret;
>> +    int64_t offset, len, nr_zones;
>> +    int i = 0;
>> +
>> +    ++optind;
>> +    offset = cvtnum(argv[optind]);
>> +    ++optind;
>> +    len = cvtnum(argv[optind]);
>> +    ++optind;
>> +    nr_zones = cvtnum(argv[optind]);
>> +
>> +    g_autofree BlockZoneDescriptor *zones = g_new(BlockZoneDescriptor, nr_zones);
>> +    ret = blk_zone_report(blk, offset, len, &nr_zones, zones);
>> +    while (i < nr_zones) {
> 
> Does blk_zone_report() set nr_zones to 0 on failure or do we need to
> check if (ret < 0) here?

ret = 0 means "no zone reported" which happen only if nr_zones is 0 or the
start offset is past the end of the disk capacity. ret < 0 would mean that
a report zone operation was actually attempted and failed (EIO, ENOMEM etc).

> 
>> +        fprintf(stdout, "start: 0x%lx, len 0x%lx, cap 0x%lx, wptr 0x%lx, "
> 
> The rest of the source file uses printf() instead of fprintf(stdout,
> ...). That's usually preferred because it's shorter.
> 
>> +                        "zcond:%u, [type: %u]\n",
> 
> Please use PRIx64 instead of lx format specifiers for portability. On
> 32-bit hosts lx is 32-bit, not 64-bit. You can grep QEMU's code for
> examples of PRIx64.
> 
>> +                zones[i].start, zones[i].length, zones[i].cap, zones[i].wp,
>> +                zones[i].cond, zones[i].type);
>> +        ++i;
>> +    }
> 
> A for loop is more idiomatic:
> 
>   for (int i = 0; i < nr_zones; i++) {
>       ...
>   }
> 
>> +    return ret;
>> +}
>> +
>> +static const cmdinfo_t zone_report_cmd = {
>> +        .name = "zone_report",
>> +        .altname = "f",
>> +        .cfunc = zone_report_f,
>> +        .argmin = 3,
>> +        .argmax = 3,
>> +        .args = "offset [offset..] len [len..] number [num..]",
> 
> The arguments are "offset len number". This command does not accept
> optional offset/len/num arguments.

The arguments should be offset + len OR offset + number of zones. Having
the 3 of them does not make sense to me. The interface would then be:

(1) offset + len -> report all zones in the block range [offset .. offset
+ len - 1]

(2) offset + number of zones -> report at most "number of zones" from the
zone containing the block at "offset".

(2) matches the semantic used at the device command level. So I prefer to
approach (1).

> 
>> +        .oneline = "report a number of zones",
> 
> Maybe "report zone information".
> 
>> +};
>> +
>> +static int zone_open_f(BlockBackend *blk, int argc, char **argv)
>> +{
>> +    int64_t offset, len;
>> +    ++optind;
>> +    offset = cvtnum(argv[optind]);
>> +    ++optind;
>> +    len = cvtnum(argv[optind]);
>> +    return blk_zone_mgmt(blk, zone_open, offset, len);
> 
> Where is the error reported? When I look at read_f() I see:
> 
>     if (ret < 0) {
>         printf("read failed: %s\n", strerror(-ret));
> 
> I think something similar is needed because qemu-io.c does not print an
> error message for us. The same is true for the other commands defined in
> this patch.
> 
>> +}
>> +
>> +static const cmdinfo_t zone_open_cmd = {
>> +        .name = "zone_open",
>> +        .altname = "f",
>> +        .cfunc = zone_open_f,
>> +        .argmin = 2,
>> +        .argmax = 2,
>> +        .args = "offset [offset..] len [len..]",
> 
> There are no optional offset/len args. The same is true for the other
> commands below.


-- 
Damien Le Moal
Western Digital Research