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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">If I recall correctly from when we implemented liblustre, which hooked into userspace using LD_PRELOAD, we had to capture the __open() call instead of open() (or something similar) to ensure
that glibc didn't bypass our LD_PRELOAD from inside of fopen().<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">You might consider downloading the source for glibc to see what it is doing in fopen().<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Calibri;color:black">Cheers, Andreas<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Calibri;color:black">-- <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Calibri;color:black">Andreas Dilger<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Calibri;color:black">Lustre Principal Architect<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Calibri;color:black">Intel High Performance Data Division</span><span style="font-size:11.0pt;font-family:Calibri"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
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<p class="MsoNormal">On 2016/06/10, 10:04, "lustre-discuss on behalf of John Bauer" <<a href="mailto:lustre-discuss-bounces@lists.lustre.org">lustre-discuss-bounces@lists.lustre.org</a> on behalf of
<a href="mailto:bauerj@iodoctors.com">bauerj@iodoctors.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p>To confirm the point that you can not intercept the open called by fopen by using LD_PRELOAD, I have written a simple test case. Note that the runtime linker never looks for open(). Only fopen()<o:p></o:p></p>
<p><b><span style="font-family:"Courier New"">$ cat a.c</span></b><span style="font-family:"Courier New""><br>
#include <unistd.h><br>
#include <stdlib.h><br>
#include <fcntl.h><br>
#include <stdio.h><br>
<br>
int<br>
main(int argc, char ** argv ){<br>
FILE *f = fopen("a", "r" ) ;<br>
fprintf(stderr,"f=%p\n",f);<br>
fclose(f);<br>
}<br>
<b>$ file a</b><br>
a: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=dfe043b4ec8cf19d5fd3fab524d7c72ed1453574, not stripped<br>
<b>$ cat a.csh</b><br>
#!/bin/csh<br>
<span style="color:red">setenv LD_DEBUG all</span><br>
./a >&! a.cpr<br>
<b>$ ./a.csh</b><br>
<b>$ grep -i open a.cpr</b><br>
120584: symbol=fopen; lookup in file=./a [0]<br>
120584: symbol=fopen; lookup in file=/lib64/libc.so.6 [0]<br>
120584: binding file ./a [0] to /lib64/libc.so.6 [0]: normal symbol `fopen' [GLIBC_2.2.5]<br>
<b>$</b></span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On 6/10/2016 7:29 AM, Ashley Pittman wrote:<o:p></o:p></p>
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<p class="MsoNormal">On 22/05/16 02:56, John Bauer wrote:<o:p></o:p></p>
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<p>Oleg<o:p></o:p></p>
<p>I can intercept the fopen(), but that does me no good as I can't set the O_LOV_DELAY_CREATE bit. What I can not intercept is the open() downstream of fopen(). If one examines the symbols in libc you will see there are no unsatisfied externals relating
to open, which means there is nothing for the runtime linker to find concerning open's. I will have a look at the Lustre 1.8 source, but I seriously doubt that the open beneath fopen() was intercepted with LD_PRELOAD. I would love to find a way to do that.
I could throw away a lot of code. Thanks, John<o:p></o:p></p>
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Could you not intercept fopen() and implement it with calls to open() and fdopen() yourself which would give you full control over what you're looking for here?<br>
<br>
Ashley.<o:p></o:p></p>
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<br>
<o:p></o:p></p>
<pre>-- <o:p></o:p></pre>
<pre>I/O Doctors, LLC<o:p></o:p></pre>
<pre>507-766-0378<o:p></o:p></pre>
<pre><a href="mailto:bauerj@iodoctors.com">bauerj@iodoctors.com</a><o:p></o:p></pre>
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