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The Basics
Id: 91583
Status: open
Priority: 0/
Queue: ExtUtils-Install

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Owner: Nobody in particular
Requestors: victor [...] vsespb.ru
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Subject: syswrite return values in not checked in run_filter
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while (my $len = sysread(SRC, $buf, $sz)) { syswrite(CMD, $buf, $len); } in this code syswrite is writing to pipe, thus can return undef + $!{EINTR} or something less than $sz bytes. just found one old report http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/62216 where person sees files truncated after this.
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On Sun Dec 22 17:35:24 2013, vsespb wrote: Show quoted text
> while (my $len = sysread(SRC, $buf, $sz)) { > syswrite(CMD, $buf, $len); > } > > in this code syswrite is writing to pipe, thus can return undef + > $!{EINTR} or something less than $sz bytes. >
The documentation for 'syswrite' (perl-5.20.1) says that it: ##### Returns the number of bytes actually written, or "undef" if there was an error (in this case the errno variable $! is also set). If the LENGTH is greater than the data available in the SCALAR after the OFFSET, only as much data as is available will be written. ##### Now, suppose that we checked the return value of 'syswrite' at the location cited. What would be the appropriate action if it were 'undef'? Thank you very much. Jim Keenan
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> > Now, suppose that we checked the return value of 'syswrite' at the > location cited. What would be the appropriate action if it were > 'undef'? >
Probably die. But problem is not when it returns undef, but when it returns undef and $!{EINTR} is set, that means there is no error, and you should retry read. Otherwise file will be partially copied. I think $!{EINTR} could happen if there were signal handlers installed and signals received. So either this should be fixed, or documented that callers should not use signals.


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