[CRIU] [PATCH 3/3] lib: add criu_check() to libcriu

[Ruslan Kuprieiev]

On 22.11.2013 14:18, Andrew Vagin wrote:
> On Fri, Nov 22, 2013 at 01:50:29PM +0400, Pavel Emelyanov wrote:
>> On 11/22/2013 01:24 PM, Andrew Vagin wrote:
>>> On Fri, Nov 22, 2013 at 12:50:58PM +0400, Pavel Emelyanov wrote:
>>>> On 11/22/2013 12:41 PM, Andrew Vagin wrote:
>>>>> On Fri, Nov 22, 2013 at 05:20:37AM +0400, Ruslan Kuprieiev wrote:
>>>>>> Signed-off-by: Ruslan Kuprieiev <kupruser at gmail.com>
>>>>>> ---
>>>>>>   lib/criu.c | 128 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>   1 file changed, 128 insertions(+)
>>>>>>
>>>>>> diff --git a/lib/criu.c b/lib/criu.c
>>>>>> index 2bd224e..f154a88 100644
>>>>>> --- a/lib/criu.c
>>>>>> +++ b/lib/criu.c
>>>>>> @@ -1,3 +1,131 @@
>>>>>>   #include "version.h"
>>>>>> +#include <sys/socket.h>
>>>>>> +#include <sys/un.h>
>>>>>> +#include <limits.h>
>>>>>> +#include <stdio.h>
>>>>>> +#include <unistd.h>
>>>>>> +#include <stdlib.h>
>>>>>> +
>>>>>> +#include "rpc.pb-c.h"
>>>>>> +
>>>>>> +#define MAX_MSG_SIZE 1024
>>>>>> +#define CR_DEFAULT_SERVICE_ADDRESS "/var/run/criu_service.socket"
>>>>>>   
>>>>>>   const char *criu_lib_version = CRIU_VERSION;
>>>>>> +
>>>>>> +static char *service_address = CR_DEFAULT_SERVICE_ADDRESS;
>>>>>> +
>>>>>> +void criu_set_service_address(char *path)
>>>>>> +{
>>>>>> +	if (path)
>>>>>> +		service_address = path;
>>>>>> +	else
>>>>>> +		service_address = CR_DEFAULT_SERVICE_ADDRESS;
>>>>>> +}
>>>>>> +
>>>>>> +static CriuResp *recv_resp(int socket_fd)
>>>>>> +{
>>>>>> +	unsigned char buf[MAX_MSG_SIZE];
>>>>>> +	int len;
>>>>>> +	CriuResp *msg = 0;
>>>>>> +
>>>>>> +	len = read(socket_fd, buf, MAX_MSG_SIZE);
>>>>>> +	if (len == -1) {
>>>>>> +		perror("Can't read response");
>>>>>> +		return NULL;
>>>>>> +	}
>>>>>> +
>>>>>> +	msg = criu_resp__unpack(NULL, len, buf);
>>>>>> +	if (!msg) {
>>>>>> +		perror("Failed unpacking response");
>>>>>> +		return NULL;
>>>>>> +	}
>>>>>> +
>>>>>> +	return msg;
>>>>>> +}
>>>>>> +
>>>>>> +static int send_req(int socket_fd, CriuReq *req)
>>>>>> +{
>>>>>> +	unsigned char buf[MAX_MSG_SIZE];
>>>>>> +	int len;
>>>>>> +
>>>>>> +	len = criu_req__get_packed_size(req);
>>>>>> +
>>>>>> +	if (criu_req__pack(req, buf) != len) {
>>>>>> +		perror("Failed packing request");
>>>>>> +		return -1;
>>>>>> +	}
>>>>>> +
>>>>>> +	if (write(socket_fd, buf, len)  == -1) {
>>>>>> +		perror("Can't send request");
>>>>>> +		return -1;
>>>>>> +	}
>>>>>> +
>>>>>> +	return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int criu_connect(void)
>>>>>> +{
>>>>>> +	int fd, ret;
>>>>>> +	struct sockaddr_un addr;
>>>>>> +	socklen_t addr_len;
>>>>>> +
>>>>>> +	fd = socket(AF_LOCAL, SOCK_SEQPACKET, 0);
>>>>>> +	if (fd < 0) {
>>>>>> +		perror("Can't create socket");
>>>>>> +		return -1;
>>>>>> +	}
>>>>>> +
>>>>>> +	memset(&addr, 0, sizeof(addr));
>>>>>> +	addr.sun_family = AF_LOCAL;
>>>>>> +
>>>>>> +	strcpy(addr.sun_path, service_address);
>>>>>> +
>>>>>> +	addr_len = strlen(addr.sun_path) + sizeof(addr.sun_family);
>>>>>> +
>>>>>> +	ret = connect(fd, (struct sockaddr *) &addr, addr_len);
>>>>>> +	if (ret < 0) {
>>>>>> +		perror("Can't connect to socket");
>>>>>> +		close(fd);
>>>>>> +	}
>>>>>> +
>>>>>> +	return fd;
>>>>>> +}
>>>>>> +
>>>>>> +int criu_check(void)
>>>>> I'm not sure that a stateless approach is good here. First of all you
>>>>> will need to connect and disconnect each time.
>>>> Why is it bad?
>>> I don't know yet.
>>>
>>>>> Can we create interface similar with dynamic linking loader (man
>>>>> dlopen).
> The correct question is:
> Why do you prefer state-less over state-full?
>
>>>>> struct criu_handle *h;
>>>>>
>>>>> h = criu_open()
>>>>> criu_check(h);
>>>>> ...
>>>>> criu_smth(h);
>>>>> ...
>>>>> criu_close(h);
>>>> We can. What are the benefits of state-full approach?
>>> * don't need to connect/disconnect each time
>> Why is it good?
> It works faster for example.

I agree with Andrew. It is easy to implement "one connection - multiple 
requests" logic, and will be much faster for set of requests.  I may 
just add one more cycle, that will process requests and fork workers.

>
>>> * asynchronous operations and iterative operations
>> We don't have async operations.
> yet
>
>>> And one more example when state-less approach doesn't work
>>>
>>> * criu_check(h) returns true
>>> * yum update criu; service criu restart
>>> * criu_dump() returns a error
>>> .
>> If updated criu fails it's a bug ;)
> I want to say, that criu_check() may start to fail after updating criu.

Should we add libcriu version(!= criu version), so if we make some 
serious changes lib will tell user to update smth?