Re: [Qemu-devel] [PATCH 2/4] scsi: build qemu-pr-helper

[Paolo Bonzini]

On 19/09/2017 15:33, Daniel P. Berrange wrote:
> On Tue, Sep 19, 2017 at 12:24:32PM +0200, Paolo Bonzini wrote:
>> Introduce a privileged helper to run persistent reservation commands.
>> This lets virtual machines send persistent reservations without using
>> CAP_SYS_RAWIO or out-of-tree patches.  The helper uses Unix permissions
>> and SCM_RIGHTS to restrict access to processes that can access its socket
>> and prove that they have an open file descriptor for a raw SCSI device.
>>
>> The next patch will also correct the usage of persistent reservations
>> with multipath devices.
>>
>> It would also be possible to support for Linux's IOC_PR_* ioctls in
>> the future, to support NVMe devices.  For now, however, only SCSI is
>> supported.
>>
>> Signed-off-by: Paolo Bonzini <address@hidden>
>> ---
> 
> 
>> +
>> +#define PR_HELPER_CDB_SIZE     16
>> +#define PR_HELPER_SENSE_SIZE   96
>> +#define PR_HELPER_DATA_SIZE    8192
>> +
>> +typedef struct PRHelperResponse {
>> +    int32_t result;
>> +    int32_t sz;
>> +    uint8_t sense[PR_HELPER_SENSE_SIZE];
>> +} PRHelperResponse;
> 
> Should we annotate this with 'packed' to ensure its immune to compiler
> padding ?

Yes...

> 
>> +typedef struct PRHelperRequest {
>> +    int fd;
>> +    size_t sz;
>> +    uint8_t cdb[PR_HELPER_CDB_SIZE];
>> +} PRHelperRequest;
> 
> Same q here ?

... and no since this one is not the wire format (which is just a
16-byte cdb, plus fd in ancillary data).

> 
>> +static int coroutine_fn prh_write_response(PRHelperClient *client,
>> +                                           PRHelperRequest *req,
>> +                                           PRHelperResponse *resp, Error 
>> **errp)
>> +{
>> +    ssize_t r;
> 
> Can just be int
> 
>> +    size_t sz;
>> +
>> +    if (req->cdb[0] == PERSISTENT_RESERVE_IN && resp->result == GOOD) {
>> +        assert(resp->sz <= req->sz && resp->sz <= sizeof(client->data));
>> +    } else {
>> +        assert(resp->sz == 0);
>> +    }
>> +
>> +    sz = resp->sz;
>> +
>> +    resp->result = cpu_to_be32(resp->result);
>> +    resp->sz = cpu_to_be32(resp->sz);
>> +    r = qio_channel_write_all(QIO_CHANNEL(client->ioc),
>> +                              (char *) resp, sizeof(*resp), errp);
>> +    if (r < 0) {
>> +        return r;
>> +    }
>> +
>> +    r = qio_channel_write_all(QIO_CHANNEL(client->ioc),
>> +                              (char *) client->data,
>> +                              sz, errp);
>> +    return r < 0 ? r : 0;
> 
> Just return 'r' directly, its only ever -1 or 0

Ok, thanks, will adjust all of these.

Paolo