Dear Suenaga,
Thanks for your reviewing. I will try to refine the patch.
For the argument length you mentioned, do you mean the "arg_length_max"
should be large enough to accept the max filename length?
IMHO, all the handling of the argument length is at receiver side in the
attachListener, such as
http://hg.openjdk.java.net/jdk/jdk/file/df3d253aaf81/src/hotspot/os/linux/attachListener_linux.cpp#l322,
for me it means that the VM side limits the argments length less than
arg_length_max, otherwise it will return NULL, which cause the sender side
(tools like jcmd and jmap) exits with error message. so I think there may be no
need to limit the argument size in tool side.
And from my experiment with jmap, the arguments send to sockets are not
arg0 only. as you can see in
http://hg.openjdk.java.net/jdk/jdk/file/df3d253aaf81/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java#l193
and
http://hg.openjdk.java.net/jdk/jdk/file/df3d253aaf81/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java#l133,
jmap can pass arg0 as "filename", and arg1 as "-live", and both of them can be
NULL. so <ver>0<cmd>0<arg>0<arg>0<arg>0 can be
<ver>0<jmap>0<filename>0<live>0, and file can be null. so 00 may not indicate
it reach the end.
BRs,
Lin
________________________________________
From: Yasumasa Suenaga <yasue...@gmail.com>
Sent: Wednesday, February 27, 2019 8:10:14 PM
To: 臧琳
Cc: David Holmes; serviceability-dev@openjdk.java.net
Subject: Re: Protocol version of Attach API
Hi Lin,
I think we need to research more about this.
IMHO we need to match length of arguments between
server (AttachListener) and client (serviceability tools) at least.
(please see previous email from me).
I have some comments for your change:
On 2019/02/27 18:22, 臧琳 wrote:
> Dear All,
> Here I have figured out one solution based on timeout. would you like
> help to see whether this is OK?
> --- a/src/hotspot/os/linux/attachListener_linux.cpp Tue Feb 26 14:57:23
> 2019 +0530
> +++ b/src/hotspot/os/linux/attachListener_linux.cpp Wed Feb 27 17:21:48
> 2019 +0800
> @@ -263,9 +263,29 @@
> int off = 0;
> int left = max_len;
>
> + memset(buf, 0, max_len);
> + // set timeout for read
> + struct timeval timeout;
> + timeout.tv_sec = 3;
> + timeout.tv_usec = 0;
I think timeout value should be configurable.
For example, we can introduce new flag in globals.hpp .
> + if(setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, (struct timeval*)&timeout,
> sizeof(timeout))) {
> + log_debug(attach)("Failed to set socket option SO_RCVTIMEO: %s\n",
> strerror(errorno));
> + printf("Warning: Failed to set socket option SO_RCVTIMEO: %s!!!\n",
> strerror(errno));
You should not use printf(), and do you need to pass '\n' to log_debug()?
> + }
> do {
> int n;
> - RESTARTABLE(read(s, buf+off, left), n);
> + log_debug(attach)("start reading data from socket....\n");
> + n = read(s, buf+off, left);
You should use RESTARTABLE macro.
read(2) might be interrupted by signal.
> + if (n < 0) {
> + if (errno == EWOULDBLOCK) {
According to man page, read(2) sets EWOULDBLOCK or EAGAIN.
So you should check both errno.
> + for (int i = str_count; i < expected_str_count; i++) {
> + //timeout, fill reminded arguments with \0;
> + buf[off+i] = '\0';
> + str_count++;
> + }
You set zero to buf[] in above.
So you can remove this loop, and set str_count to expected_str_count
without manipulating buf[].
In addition, I prefer to add log_debug() at this
to record NULL arguments are added.
> + break;;
> + }
> + }
> assert(n <= left, "buffer was too small, impossible!");
> buf[max_len - 1] = '\0';
> if (n == -1) {
Thanks,
Yasumasa
> Thanks.
> Lin
>
> ________________________________________
> From: Yasumasa Suenaga <yasue...@gmail.com>
> Sent: Wednesday, February 27, 2019 15:15
> To: David Holmes; 臧琳
> Cc: serviceability-dev@openjdk.java.net
> Subject: Re: Protocol version of Attach API
>
> On 2019/02/27 15:59, David Holmes wrote:
>> On 27/02/2019 4:10 pm, Yasumasa Suenaga wrote:
>>> Hi,
>>>
>>> Buffer size for receiving packets from client is determined at [1].
>>
>> Maximum buffer size, yes.
>>
>>> It defines length of command name and of argument.
>>> It is passed via Unix domain, so we fill '\0' to remaining bytes and
>>> might be able to assume all arguments are passed with empty string.
>>
>> Not sure what you mean.
>>
>> // The buffer is expected to be formatted as follows:
>> // <ver>0<cmd>0<arg>0<arg>0<arg>0
>>
>> so we can expect to read at least two things - the ver and cmd. If we
>> encounter 00 we can infer we reached the end. But we may not have read the
>> full data into the buffer, so can't tell if another call to read() is needed
>> yet - you only know after you've read the 00.
>>
>>> BTW length of arguments is defined to 1024 in [2].
>>> jcmd and jmap might pas file path - it might be JVM_MAXPATHLEN (4097 bytes).
>>> Buffer size which is used in AttachListener seems not to be enough.
>>
>> One has to assume/hope that the code sending the data is working to the same
>> protocol rules as the receiver! Otherwise this is just completely broken.
>
> On Linux, client (VirtualMachineImpl) seems not to check length of arguments:
>
> http://hg.openjdk.java.net/jdk/jdk/file/df3d253aaf81/src/jdk.attach/linux/classes/sun/tools/attach/VirtualMachineImpl.java#l168
>
> In case of jcmd, all options are passed to arg #1. It seems not to check the
> length:
>
> http://hg.openjdk.java.net/jdk/jdk/file/df3d253aaf81/src/jdk.jcmd/share/classes/sun/tools/jcmd/JCmd.java#l111
>
>
> I guess other tools (jstack, jmap, etc) which connect to AttachListener are
> same.
> So we can fix both Attach API and AttachListener (it will be big change!),
> but I concern we can keep protocol version...
>
>
> Thanks,
>
> Yasumasa
>
>
>> David
>> -----
>>
>>> We might have to change more.
>>>
>>>
>>> Thanks,
>>>
>>> Yasumasa
>>>
>>>
>>> [1]
>>> http://hg.openjdk.java.net/jdk/jdk/file/df3d253aaf81/src/hotspot/os/linux/attachListener_linux.cpp#l254
>>> [2]
>>> http://hg.openjdk.java.net/jdk/jdk/file/df3d253aaf81/src/hotspot/share/services/attachListener.hpp#l106
>>>
>>>
>>> On 2019/02/27 15:00, 臧琳 wrote:
>>>> Another solution I can figure out is try to add timeout for socket read. I
>>>> will also investigate whether is works.
>>>>
>>>> Cheers,
>>>> Lin
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: 臧琳
>>>>> Sent: Wednesday, February 27, 2019 1:52 PM
>>>>> To: 'David Holmes' <david.hol...@oracle.com>; Yasumasa Suenaga
>>>>> <yasue...@gmail.com>
>>>>> Cc: serviceability-dev@openjdk.java.net
>>>>> Subject: RE: Protocol version of Attach API
>>>>>
>>>>> Dear David, Yasumasa,
>>>>> I think it is hard to know how long the buffer is passed from
>>>>> socket
>>>>> without changing the info of the message from the receiver side.
>>>>> So how about when str_count reach to 3, we test it with
>>>>> non_blocking
>>>>> read?
>>>>>
>>>>>
>>>>> Cheers,
>>>>> Lin
>>>>>> -----Original Message-----
>>>>>> From: David Holmes <david.hol...@oracle.com>
>>>>>> Sent: Wednesday, February 27, 2019 1:44 PM
>>>>>> To: Yasumasa Suenaga <yasue...@gmail.com>; 臧琳 <zangl...@jd.com>
>>>>>> Cc: serviceability-dev@openjdk.java.net
>>>>>> Subject: Re: Protocol version of Attach API
>>>>>>
>>>>>> Hi Yasumasa,
>>>>>>
>>>>>> On 27/02/2019 1:05 pm, Yasumasa Suenaga wrote:
>>>>>>> Hi Lin,
>>>>>>>
>>>>>>> My proposal is a just idea, so you need to tweak it.
>>>>>>>
>>>>>>> AttachListener receives raw command.
>>>>>>> For example, jcmd is `jcmd\0<arg strings>`. Please see
>>>>>>> HotSpotVirtualMachine and extended classes.
>>>>>>>
>>>>>>> In case of jcmd, I guess AttachListener will receive message
>>>>>>> `<version>\0jcmd\0<args>\0\0\0` (I did not check it well).
>>>>>>> So I guess we can add '\0' when `str_count` does not reach to maximum.
>>>>>>
>>>>>> I don't see how this approach can work. You have to know how many
>>>>>> arguments are coming in the "packet", but that information is not
>>>>>> available in the current Linux implementation.Without it you can't
>>>>>> know when to stop calling read().
>>>>>>
>>>>>> The protocol would need to be changed to send the "packet" size, but
>>>>>> that's not compatible with older JDKs.
>>>>>>
>>>>>> Otherwise I think we have no choice but to use a non-blocking read ...
>>>>>> though I'm still unsure if you can know for certain that you've
>>>>>> reached the end of the "packet" ...
>>>>>>
>>>>>> Thanks,
>>>>>> David
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Yasumasa
>>>>>>>
>>>>>>>
>>>>>>> On 2019/02/27 11:50, zangl...@jd.com wrote:
>>>>>>>> Dear Yasumasa,
>>>>>>>> The fix you mentioned seems not work as expected.
>>>>>>>> I have done an experiment that use jdk1.8's "jcmd <pid> help" to
>>>>>>>> attach to latest jdk.
>>>>>>>> it seem the whole "jcmd <pid> help" buffer is not
>>>>>>>> read completely at one time. in my case it is "jcmd", "<pid>",
>>>>>>>> "help", and then block at while().
>>>>>>>> After applied your change, it seems only the "jcmd" is
>>>>>>>> processed, the "<pid>", "help" is replaced by '\0'.
>>>>>>>>
>>>>>>>> BRs,
>>>>>>>> Lin
>>>>>>>>
