Some more perlio doc tweaks based on NI-S.

[p5sagit/p5-mst-13.2.git] / pod / perlrun.pod

diff --git a/pod/perlrun.pod b/pod/perlrun.pod
index d8ed107..81d4749 100644 (file)
--- a/pod/perlrun.pod
+++ b/pod/perlrun.pod
@@ -947,9 +947,23 @@ You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
 
 =item :crlf
 
-A layer that implements DOS/Windows like CRLF line endings.
-On read converts pairs of CR,LF to a single "\n" newline character.
-On write converts each "\n" to a CR,LF pair.
+A layer that implements DOS/Windows like CRLF line endings.  On read
+converts pairs of CR,LF to a single "\n" newline character.  On write
+converts each "\n" to a CR,LF pair.  Note that this layer likes to be
+one of its kind: it silently ignores attempts to be pushed into the
+layer stack more than once.
+
+(Gory details follow) To be more exact what happens is this: after
+pushing itself to the stack, the C<:crlf> layer checks all the layers
+below itself to find the first layer that is capable of being a CRLF
+layer but is not yet enabled to be a CRLF layer.  If it finds such a
+layer, it enables the CRLFness of that other deeper layer, and then
+pops itself off the stack.  If not, fine, use the one we just pushed.
+
+The end result is that a C<:crlf> means "please enable the first CRLF
+layer you can find, and if you can't find one, here would be a good
+spot to place a new one."
+
 Based on the C<:perlio> layer.
 
 =item :mmap
@@ -1125,12 +1139,26 @@ the pseudorandom seed supplied by the operating system and libraries.
 This means that each different run of Perl will have a different
 ordering of the results of keys(), values(), and each().
 
-See L<perlsec/"Algorithmic Complexity Attacks"> for more information.
+B<Please note that the hash seed is sensitive information>. Hashes are
+randomized to protect against local and remote attacks against Perl
+code. By manually setting a seed this protection may be partially or
+completely lost.
+
+See L<perlsec/"Algorithmic Complexity Attacks"> and
+L</PERL_HASH_SEED_DEBUG> for more information.
 
 =item PERL_HASH_SEED_DEBUG
 
-(Since Perl 5.8.1.)  Set to "1" to display (to STDERR) the value of
-the hash seed at the beginning of execution.
+(Since Perl 5.8.1.)  Set to one to display (to STDERR) the value of
+the hash seed at the beginning of execution.  This, combined with
+L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
+behavior caused by hash randomization.
+
+B<Note that the hash seed is sensitive information>: by knowing it one
+can craft a denial-of-service attack against Perl code, even remotely,
+see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
+B<Do not disclose the hash seed> to people who don't need to know it.
+See also hash_seed() of L<Hash::Util>.
 
 =item PERL_ROOT (specific to the VMS port)