Re: [v5][PATCH 11/16] tools/libxl: detect and avoid conflicts with RDM

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 2015/7/7 19:57, Ian Jackson wrote:
> Tiejun Chen writes ("[v5][PATCH 11/16] tools/libxl: detect and avoid conflicts with RDM"):
>> While building a VM, HVM domain builder provides struct hvm_info_table{}
>> to help hvmloader. Currently it includes two fields to construct guest
>> e820 table by hvmloader, low_mem_pgend and high_mem_pgend. So we should
>> check them to fix any conflict with RDM.
> ...
>> +    *nr_entries = 0;
>> +    rc = xc_reserved_device_memory_map(CTX->xch, flag, seg, bus, devfn,
>> +                                       NULL, nr_entries);
>> +    assert(rc <= 0);
>> +    /* "0" means we have no any rdm entry. */
>> +    if (!rc)
>> +        goto out;
>
> I think the error handling here is wrong.  Certainly `rc' should not
> be used for a libxc return.

Nope, we don't return rc directly. In any case of error, rc is reset as 
"ERROR_FAIL" finally.

>
> See tools/libxl/CODING_STYLE.  I know that much of the existing code
> uses rc for libxc returns but this is deprecated, and please don't
> make more of it.
>
>> +    if (errno == ENOBUFS) {
>> +        *xrdm = libxl__malloc(gc,
>> +                              *nr_entries *
>> +                              sizeof(xen_reserved_device_memory_t));
>> +        rc = xc_reserved_device_memory_map(CTX->xch, flag, seg, bus, devfn,
>> +                                           *xrdm, nr_entries);
>
> This might be less code, and a bit clearer, if it were a loop rather
> than two calls with the second in an if.

Sorry I can't understand completely what you want to do. But I really 
agree we should improve this chunk of codes, what about this?

     if (errno != ENOBUFS) {
         rc = ERROR_FAIL;
         goto out;
     }

     *xrdm = libxl__malloc(gc,
                           *nr_entries * 
sizeof(xen_reserved_device_memory_t));
     rc = xc_reserved_device_memory_map(CTX->xch, flag, seg, bus, devfn,
                                        *xrdm, nr_entries);
     if (rc)
         rc = ERROR_FAIL;

  out:
     if (rc) {
         *nr_entries = 0;
         *xrdm = NULL;
         LOG(ERROR, "Could not get reserved device memory maps.\n");
     }
     return rc;

I think this make more readable and clear.

>
> ...
>> +        if(d_config->rdms[i].flag == LIBXL_RDM_RESERVE_FLAG_STRICT) {
>               ^
> Missing space.
>

Fixed.

Thanks
Tiejun