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
