Comments on: Fab tool: watch http://openquery.com/blog/fab-tool-watch About MySQL, Drizzle, MariaDB and more! Wed, 13 Jan 2010 12:40:20 +0000 http://wordpress.org/?v=2.8 hourly 1 By: Sergei Golubchik http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1564 Sergei Golubchik Mon, 29 Jun 2009 21:19:42 +0000 http://openquery.com/blog/?p=849#comment-1564 I wonder where you got it from. It sounded so unbelievable that I took the time to download the source of watch.c and look inside. Indeed, no crazy program counter manipulations. Pretty ordinary stuff - popen(), getc() until eof, pclose(), wait, repeat. Nothing too fancy. I wonder where you got it from. It sounded so unbelievable that I took the time to download the source of watch.c and look inside.

Indeed, no crazy program counter manipulations. Pretty ordinary stuff – popen(), getc() until eof, pclose(), wait, repeat. Nothing too fancy.

]]> By: Wayne http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1561 Wayne Mon, 29 Jun 2009 17:49:28 +0000 http://openquery.com/blog/?p=849#comment-1561 I'm not quite sure where you got that idea from, but watch(1) uses popen(3) so it execs a new process every time. I’m not quite sure where you got that idea from, but watch(1) uses popen(3) so it execs a new process every time.

]]> By: Eric Bergen http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1559 Eric Bergen Mon, 29 Jun 2009 16:51:39 +0000 http://openquery.com/blog/?p=849#comment-1559 Looking at the source it does a popen() pclose() for each iteration. I don't see any poking in the version from: cvs -d :pserver:anoncvs@sources.redhat.com:/cvs/procps co procps The man page also says it's just passed to a shell. Looking at the source it does a popen() pclose() for each iteration. I don’t see any poking in the version from:

cvs -d :pserver:anoncvs@sources.redhat.com:/cvs/procps co procps

The man page also says it’s just passed to a shell.

]]> By: Jeremy Cole http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1558 Jeremy Cole Mon, 29 Jun 2009 16:38:04 +0000 http://openquery.com/blog/?p=849#comment-1558 Hi Arjen, I'm sorry, but unless you're talking about a different 'watch' than the one that ships with, well probably every Linux out there, you're just wrong. Where did you get this idea? You didn't provide any reference whatsoever. http://procps.cvs.sourceforge.net/viewvc/procps/procps/watch.c?view=markup You can see quite clearly that it calls p = popen(...) ... getc(p) ... pclose(p) Compare the file available at the above URL to the one available in your operating system of choice. (Compared and matched to CentOS's myself.) Regards, Jeremy Hi Arjen,

I’m sorry, but unless you’re talking about a different ‘watch’ than the one that ships with, well probably every Linux out there, you’re just wrong. Where did you get this idea? You didn’t provide any reference whatsoever.

http://procps.cvs.sourceforge.net/viewvc/procps/procps/watch.c?view=markup

You can see quite clearly that it calls p = popen(…) … getc(p) … pclose(p)

Compare the file available at the above URL to the one available in your operating system of choice. (Compared and matched to CentOS’s myself.)

Regards,

Jeremy

]]> By: Holger Hoffstätte http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1557 Holger Hoffstätte Mon, 29 Jun 2009 16:23:39 +0000 http://openquery.com/blog/?p=849#comment-1557 I have no idea what version of watch you have been looking at, but the one from procps (on SourceForge) restarts the process after it terminates. I have no idea what version of watch you have been looking at, but the one from procps (on SourceForge) restarts the process after it terminates.

]]> By: Giuseppe Maxia http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1555 Giuseppe Maxia Mon, 29 Jun 2009 07:37:34 +0000 http://openquery.com/blog/?p=849#comment-1555 Arjen, care to share the evidence on your claim? Looking at watch source code, I could only see a "getc" on the child process pointer (created by popen). Where did you get the "poke" stuff? Giuseppe Arjen,
care to share the evidence on your claim? Looking at watch source code, I could only see a “getc” on the child process pointer (created by popen). Where did you get the “poke” stuff?

Giuseppe

]]> By: strcmp http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1554 strcmp Mon, 29 Jun 2009 07:25:11 +0000 http://openquery.com/blog/?p=849#comment-1554 If you have a 'some ... kernel bug', you have other problems than watch causing a segfault in the watched program... If all it does is using official interfaces, this is not different than using a debugger, etc. I have seen more database errors than watch errors, watch doesn't seem to be that problematic. I actually downloaded an read watch.c (from procps 3.2.7-9ubuntu2.1) to see how it works, if there are script interpreters, dynamic loading and initialization of global variables involved. In line 264 you have: if (!(p = popen(command, "r"))) { perror("popen"); do_exit(2); } Very hacky indeed :) Which (maybe prehistoric?) version of watch is you information about? If you have a ’some … kernel bug’, you have other problems than watch causing a segfault in the watched program… If all it does is using official interfaces, this is not different than using a debugger, etc. I have seen more database errors than watch errors, watch doesn’t seem to be that problematic.

I actually downloaded an read watch.c (from procps 3.2.7-9ubuntu2.1) to see how it works, if there are script interpreters, dynamic loading and initialization of global variables involved. In line 264 you have:

if (!(p = popen(command, “r”))) {
perror(”popen”);
do_exit(2);
}

Very hacky indeed :) Which (maybe prehistoric?) version of watch is you information about?

]]> By: figvam http://openquery.com/blog/fab-tool-watch/comment-page-1#comment-1553 figvam Mon, 29 Jun 2009 06:07:18 +0000 http://openquery.com/blog/?p=849#comment-1553 > That is, until you learn how it works. It does not re-load and run the program, oh no it’s much smarter than that: it goes in and resets the program counter. That’s right, it literally pokes into its child process! Where did you get that? Looking at the source, it uses nothing more than popen/pclose to run a child program: http://procps.cvs.sourceforge.net/viewvc/procps/procps/watch.c?revision=1.16&view=markup Indeed, if you check the process list while watch is running, you can see the pids of the child processes incrementing with each run. There's nothing suspicious here, and certainly no poking around the program counters. > That is, until you learn how it works. It does not re-load and run the program, oh no it’s much smarter than that: it goes in and resets the program counter. That’s right, it literally pokes into its child process!

Where did you get that? Looking at the source, it uses nothing more than popen/pclose to run a child program:
http://procps.cvs.sourceforge.net/viewvc/procps/procps/watch.c?revision=1.16&view=markup

Indeed, if you check the process list while watch is running, you can see the pids of the child processes incrementing with each run. There’s nothing suspicious here, and certainly no poking around the program counters.

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