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Re: [libvirt] [PATCH] libxl: Check for regcomp failure



On 04.09.2013 22:18, Eric Blake wrote:
> On 09/04/2013 02:03 PM, Jim Fehlig wrote:
>>>
>>> Yeah, good question.  I found a few occurrences of regcomp() and friends
>>> throughout the sources and most seem to do regfree() even when regcomp()
>>> fails.  The man page is not very clear, but the notes on regfree()
>>> suggest it is not necessary
>>>
>>>   POSIX Pattern Buffer Freeing
>>>     Supplying regfree() with a precompiled pattern buffer, preg will
>>>     free the memory allocated to the pattern buffer by the compiling
>>>     process, regcomp().
>>>
>>> But does the pattern buffer contain any allocated memory when regcomp()
>>> fails?  The notes on regcomp() are not clear about this.
> 
> Thankfully, we can read the source :)
> 
> In glibc, regcomp assigns into preg, but is careful to undo any
> allocation on failure; it is also careful to make regfree() a no-op on
> an already-freed buffer (whether by calling regfree() twice in a row, or
> using it on preg after a failed regcomp).  Gnulib copies this behavior.
>  But it is not universally standard:

Question then is: if regcomp(&reg, ...) fails, reg == NULL, right? But
passing the @reg to regerror: regerror(errcode, &reg, ...) doesn't make
much sense then. It can make, if regcomp would free all mem allocated,
but set @reg to different values (each of them representing different
cause of error). If that is the case, <irony>this is what I call the
design!</irony>

Michal


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