Re: [Xen-devel] [PATCH] libxc: Have xc_translate_foreign_address() set errno properly

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 03/03/2016 02:47 PM, Wei Liu wrote:
> On Wed, Mar 02, 2016 at 08:51:51AM +0200, Razvan Cojocaru wrote:
>> Currently it's possible for xc_translate_foreign_address() to fail
>> and errno still be set to success. This patch fixes the issue.
>> Based on the first half of Don Slutz' patch:
>> http://lists.xen.org/archives/html/xen-devel/2014-03/msg03720.html
>>
>> Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
>> ---
>>  tools/libxc/xc_pagetab.c | 36 +++++++++++++++++++++++++++++++++---
>>  1 file changed, 33 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/libxc/xc_pagetab.c b/tools/libxc/xc_pagetab.c
>> index ec97890..f7dc30b 100644
>> --- a/tools/libxc/xc_pagetab.c
>> +++ b/tools/libxc/xc_pagetab.c
>> @@ -34,9 +34,14 @@ unsigned long xc_translate_foreign_address(xc_interface 
>> *xch, uint32_t dom,
>>      int size, level, pt_levels = 2;
>>      void *map;
>>  
>> -    if (xc_domain_getinfo(xch, dom, 1, &dominfo) != 1 
>> +    if (xc_domain_getinfo(xch, dom, 1, &dominfo) != 1
>>          || dominfo.domid != dom)
>> +    {
>> +        if (errno == 0)
>> +            errno = EINVAL;
>> +
>>          return 0;
>> +    }
>>  
> 
> Shouldn't we look into fixing the libxc functions that fail to set errno?
> 
> With an approach like this you end up getting whatever errno set prior
> to calling xc_ function, which isn't very helpful in any case.

Yes, you're right. I took that part of Don's patch a while ago and ran
with it, but a better approach would be indeed to make sure that all
those functions do set errno properly - so I'll check to see if they do.

The only exception is the "if (!(pte & 1))" case, where errno should
just be set directly I think.

I'll see if I can spin this into a V2.


Thanks,
Razvan

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