Re: [Qemu-devel] [Qemu-ppc] [PATCH] spapr_vscsi: Fix REPORT_LUNS handling

[Alexander Graf]

On 02.01.2014, at 16:31, Alexander Graf <address@hidden> wrote:

> 
> On 18.10.2013, at 14:33, Nathan Whitehorn <address@hidden> wrote:
> 
>> Intercept REPORT_LUNS commands addressed either to SRP LUN 0 or the 
>> well-known
>> LUN for REPORT_LUNS commands. This is required to implement the SAM and SPC
>> specifications.
>> 
>> Since SRP implements only a single SCSI target port per connection, the SRP
>> target is required to report all available LUNs in response to a REPORT_LUNS
>> command addressed either to LUN 0 or the well-known LUN. Instead, QEMU was
>> forwarding such requests to the first QEMU SCSI target, with the result that
>> initiators that relied on this feature would only see LUNs on the first QEMU
>> SCSI target.
>> 
>> Behavior for REPORT_LUNS commands addressed to any other LUN is not specified
>> by the standard and so is left unchanged. This preserves behavior under Linux
>> and SLOF, which enumerate possible LUNs by hand and so address no commands
>> either to LUN 0 or the well-known REPORT_LUNS LUN.
>> 
>> Signed-off-by: Nathan Whitehorn <address@hidden>
> 
> This patch fails on checkpatch.pl. Please fix those warnings up :).
> 
> WARNING: braces {} are necessary for all arms of this statement
> #65: FILE: hw/scsi/spapr_vscsi.c:738:
> +        if (dev->channel == 0 && dev->id == 0 && dev->lun == 0)
> [...]
> 
> WARNING: braces {} are necessary for all arms of this statement
> #81: FILE: hw/scsi/spapr_vscsi.c:754:
> +        if (dev->id == 0 && dev->channel == 0)
> [...]
> +        else
> [...]
> 
> WARNING: line over 80 characters
> #108: FILE: hw/scsi/spapr_vscsi.c:781:
> +    if ((srp->cmd.lun == 0 || be64_to_cpu(srp->cmd.lun) == 
> SRP_REPORT_LUNS_WLUN)      && srp->cmd.cdb[0] == REPORT_LUNS) {
> 
> total: 0 errors, 3 warnings, 75 lines checked
> 
> Your patch has style problems, please review.  If any of these errors
> are false positives report them to the maintainer, see
> CHECKPATCH in MAINTAINERS.
> 
>> ---
>> hw/scsi/spapr_vscsi.c | 57 
>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 57 insertions(+)
>> 
>> diff --git a/hw/scsi/spapr_vscsi.c b/hw/scsi/spapr_vscsi.c
>> index 2a26042..87e0fb3 100644
>> --- a/hw/scsi/spapr_vscsi.c
>> +++ b/hw/scsi/spapr_vscsi.c
>> @@ -63,6 +63,8 @@
>> #define SCSI_SENSE_BUF_SIZE     96
>> #define SRP_RSP_SENSE_DATA_LEN  18
>> 
>> +#define SRP_REPORT_LUNS_WLUN    0xc10100000000000
>> +
>> typedef union vscsi_crq {
>>    struct viosrp_crq s;
>>    uint8_t raw[16];
>> @@ -720,12 +722,67 @@ static void vscsi_inquiry_no_target(VSCSIState *s, 
>> vscsi_req *req)
>>    }
>> }
>> 
>> +static void vscsi_report_luns(VSCSIState *s, vscsi_req *req)
>> +{
>> +    BusChild *kid;
>> +    int i, len, n, rc;
>> +    uint8_t *resp_data;
>> +    bool found_lun0;
>> +
>> +    n = 0;
>> +    found_lun0 = false;
>> +    QTAILQ_FOREACH(kid, &s->bus.qbus.children, sibling) {
>> +        SCSIDevice *dev = SCSI_DEVICE(kid->child);
>> +
>> +        n += 8;
>> +        if (dev->channel == 0 && dev->id == 0 && dev->lun == 0)
>> +            found_lun0 = true;
>> +    }
>> +    if (!found_lun0) {
>> +        n += 8;
>> +    }
>> +    len = n+8;
> 
> Let me try to grasp what you're doing here. You're trying to figure out how 
> many devices there are attached to the bus. For every device you reserve a 
> buffer block. Lun0 is mandatory, all others are optional.
> 
> First off, I think the code would be easier to grasp if you'd count "number 
> of entries" rather than "number of bytes". That way we don't have to mentally 
> deal with the 8 byte block granularity.
> 
> Then IIUC you're jumping through a lot of hoops to count lun0 if it's there, 
> but keep it reserved when it's not there. Why don't you just always reserve 
> entry 0 for lun0? In the loop where you're actually filling in data you just 
> skip lun0. Or is lun0 a terminator and always has to come last?
> 
> 
>> +
>> +    resp_data = malloc(len);
> 
> g_malloc0
> 
>> +    memset(resp_data, 0, len);
>> +    stl_be_p(resp_data, n);
>> +    i = found_lun0 ? 8 : 16;
>> +    QTAILQ_FOREACH(kid, &s->bus.qbus.children, sibling) {
>> +        DeviceState *qdev = kid->child;
>> +        SCSIDevice *dev = SCSI_DEVICE(qdev);
>> +
>> +        if (dev->id == 0 && dev->channel == 0)
>> +            resp_data[i] = 0;
>> +        else
>> +            resp_data[i] = (2 << 6);

Ah, I almost forgot this one. Please convert that into something more verbose 
through a define. Whatever that bit means ... :).

>> +        resp_data[i] |= dev->id;
>> +        resp_data[i+1] = (dev->channel << 5);
>> +        resp_data[i+1] |= dev->lun;

What are the other 6 bytes reserved for?


Alex