Re: [Qemu-devel] [PATCH] qemu-nbd: only send a limited number of errno codes on the wire

[Max Reitz <mreitz@redhat.com>]

On 08.05.2015 14:45, Max Reitz wrote:
> On 07.05.2015 17:26, Paolo Bonzini wrote:
>> Right now, NBD includes potentially platform-specific error values in
>> the wire protocol.
>>
>> Luckily, most common error values are more or less universal: in
>> particular, of all errno values <= 34 (up to ERANGE), they are all
>> the same on supported platforms except for 11 (which is EAGAIN on
>> Windows and Linux, but EDEADLK on Darwin and the *BSDs).
>>
>> So, in order to guarantee some portability, only keep a dozen
>> possible error codes and squash everything else to EINVAL.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>   nbd.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 47 insertions(+)
>>
>> diff --git a/nbd.c b/nbd.c
>> index eea8c51..1ad5b66 100644
>> --- a/nbd.c
>> +++ b/nbd.c
>> @@ -86,6 +86,37 @@
>>   #define NBD_OPT_ABORT           (2)
>>   #define NBD_OPT_LIST            (3)
>>   +/* NBD errors are based on errno numbers, so there is a 1:1 mapping,
>> + * but only a limited set of errno values is specified in the protocol.
>> + * Everything else is squashed to EINVAL.
>> + */
>> +static int system_errno_to_nbd_errno(int err)
>> +{
>> +    switch (err) {
>> +    case EPERM:
>> +        return 1;
>> +    case EIO:
>> +        return 5;
>> +    case ENXIO:
>> +        return 6;
>> +    case E2BIG:
>> +        return 7;
>> +    case ENOMEM:
>> +        return 12;
>> +    case EACCES:
>> +        return 13;
>> +    case EFBIG:
>> +        return 27;
>> +    case ENOSPC:
>> +        return 28;
>> +    case EROFS:
>> +        return 30;
>> +    case EINVAL:
>> +    default:
>> +        return 22;
>> +    }
>> +}
>> +
>>   /* Definitions for opaque data types */
>>     typedef struct NBDRequest NBDRequest;
>> @@ -856,6 +887,20 @@ ssize_t nbd_receive_reply(int csock, struct 
>> nbd_reply *reply)
>>       reply->error  = be32_to_cpup((uint32_t*)(buf + 4));
>>       reply->handle = be64_to_cpup((uint64_t*)(buf + 8));
>>   +    /* NBD errors should be universally equal to the corresponding
>> +     * errno values, check it here.
>> +     */
>> +    QEMU_BUILD_BUG_ON(EPERM != 1);
>> +    QEMU_BUILD_BUG_ON(EIO != 5);
>> +    QEMU_BUILD_BUG_ON(ENXIO != 6);
>> +    QEMU_BUILD_BUG_ON(E2BIG != 7);
>> +    QEMU_BUILD_BUG_ON(ENOMEM != 12);
>> +    QEMU_BUILD_BUG_ON(EACCES != 13);
>> +    QEMU_BUILD_BUG_ON(EINVAL != 22);
>> +    QEMU_BUILD_BUG_ON(EFBIG != 27);
>> +    QEMU_BUILD_BUG_ON(ENOSPC != 28);
>> +    QEMU_BUILD_BUG_ON(EROFS != 30);
>> +
>
> Why no nbd_errno_to_system_errno() function?

Oops, I missed v2. Sorry.

Max