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Re: problem when run tcp/udp probing script

From: fche at redhat dot com (Frank Ch. Eigler)
To: ch huang <justlooks at gmail dot com>
Cc: systemtap at sourceware dot org
Date: Mon, 19 Mar 2012 09:53:46 -0400
Subject: Re: problem when run tcp/udp probing script
References: <CACeqxwR3yeQMQZ7+eg0RXzK2bcaHspvrvWsBpJbZ3POq9FtX0g@mail.gmail.com>

ch huang <justlooks@gmail.com> writes:

> [...]
> probe tcp.recvmsg {
> printf("%s: TCP: Receiving message. Socket %d. Size %d\n", execname(),
> sock, size)
> }
> [...]
> but why the value of socket is negative?
>
> mysqld: TCP: Receiving message. Socket -131937697852800. Size 4
> mysqld: TCP: Receiving message. Socket -131937398508736. Size 16384
> mysqld: TCP: Receiving message. Socket -131938374336384. Size 1
> mysqld: TCP: Receiving message. Socket -131937398508736. Size 16384

Because sock is a pointer to a kernel structure.  If you print it as
%p, you'll see them as pretty reasonable values 0xffff8800b410c080
etc.

- FChE

References:
- problem when run tcp/udp probing script
  - From: ch huang

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