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Re: Curious Behavior doing routine redirection of ping output to (selinux: message 2 of 12) file...



On Wednesday 04 January 2006 06:11, Gregory Maxwell <gmaxwell gmail com> 
wrote:
> Would it be inappropriate add a compile time flag to bash to cause
> such redirection to always bounce through the shell? Obviously there
> would be a performance hit... but the mysterious failure is probably
> worse...

Mysterious failures are a bad thing.  But the performance hit of proxying the 
data would also be bad.

Also note that there are some unusual features that some programs may rely on, 
for example when you see the following you may think that the file is 
append-only:

program > output

However that is not the case.  The program can seek in the file, EG it can 
seek back to 0 to re-write the file if it wishes.

program < input

The above command permits seeking in the input file to read from different 
locations.

Some programs rely on this type of functionality, for example the mpg123 
program to play MP3 files would do exactly that.  Commands such as
"zcat file.mp3.gz | mpg123 -" didn't work because seeks failed on the pipe.  I 
wrote a patch for mpg123 that used fopen() and fseek() as the stdio buffers 
were large enough to allow the 100 byte reverse seeks that mpg123 relied on.

Tracking down many programs that are similarly buggy and writing work-arounds 
for them would not be fun.

-- 
http://www.coker.com.au/selinux/   My NSA Security Enhanced Linux packages
http://www.coker.com.au/bonnie++/  Bonnie++ hard drive benchmark
http://www.coker.com.au/postal/    Postal SMTP/POP benchmark
http://www.coker.com.au/~russell/  My home page


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