Re: strace write/read output

[Eric Bambach <eric@cisu.net>]

(forgot to cc the list)

On Tuesday 22 March 2005 12:16 pm, you wrote:
> > On Tuesday 22 March 2005 11:05 am, Fabio Miranda Hamburger wrote:
> > > hello,
> > >
> > > I am debugging a tcpip app on linux, I would like to use strace to show
> > > me *all* the data passed to read() and write() function to the sockets
> > > stream.
> > >
> > > thanks,
> >
> >       Does strace with the -e option do what you want? man strace. It
> > seems to do read and write. Prepare for big logfiles ;)
>
> I was trying to figure out how to do it. Can you provide an example?
> Usually strace shows few characters and at the end, the total length of
> what was received. Well, I need the entire string of characters.

Here is a quick and dirty example on a small text file. Notice I dont know 
what fd's cat uses so I just guessed 1-5. Below is the output of the example 
too. It outputs the ENTIRE file that was read in hex and ascii you just have 
to know what file desciptors you want to trace. To trace write calls this way 
just change -e read=1,2,3,4,5 to -e write=1,2,3,4,5 or you could even use 
them together.

command:
strace -e read=1,2,3,4,5 -o file.log cat unison.log

Outputs this to file.log (truncated for sake of the mailer and example):

read(3, "Fatal error: Lost connection wit"..., 131072) = 270
46 61 74 61 6c 20 65 72  72 6f 72 3a 20 4c 6f 73  Fatal er ror: Los |
74 20 63 6f 6e 6e 65 63  74 69 6f 6e 20 77 69 74  t connec tion wit |
68 20 74 68 65 20 73 65  72 76 65 72 0a 46 61 74  h the se rver.Fat |
61 6c 20 65 72 72 6f 72  3a 20 4c 6f 73 74 20 63  al error : Lost c |
6f 6e 6e 65 63 74 69 6f  6e 20 77 69 74 68 20 74  onnectio n with t |
68 65 20 73 65 72 76 65  72 0a 46 61 74 61 6c 20  he serve r.Fatal  |
65 72 72 6f 72 3a 20 4c  6f 73 74 20 63 6f 6e 6e  error: L ost conn |
65 63 74 69 6f 6e 20 77  69 74 68 20 74 68 65 20  ection w ith the  |
73 65 72 76 65 72 0a 46  61 74 61 6c 20 65 72 72  server.F atal err |
6f 72 3a 20 4c 6f 73 74  20 63 6f 6e 6e 65 63 74  or: Lost  connect |
69 6f 6e 20 77 69 74 68  20 74 68 65 20 73 65 72  ion with  the ser |
76 65 72 0a 46 61 74 61  6c 20 65 72 72 6f 72 3a  ver.Fata l error: |
20 4c 6f 73 74 20 63 6f  6e 6e 65 63 74 69 6f 6e   Lost co nnection |
20 77 69 74 68 20 74 68  65 20 73 65 72 76 65 72   with th e server |
0a 46 61 74 61 6c 20 65  72 72 6f 72 3a 20 4c 6f  .Fatal e rror: Lo |
73 74 20 63 6f 6e 6e 65  63 74 69 6f 6e 20 77 69  st conne ction wi |
 74 68 20 74 68 65 20 73  65 72 76 65 72 0a        th the s erver.   |

-- 
----------------------------------------
--EB

> All is fine except that I can reliably "oops" it simply by trying to read
> from /proc/apm (e.g. cat /proc/apm).
> oops output and ksymoops-2.3.4 output is attached.
> Is there anything else I can contribute?

The latitude and longtitude of the bios writers current position, and
a ballistic missile.

                --Alan Cox LKML-December 08,2000 

----------------------------------------
-
To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html