Re: [Libguestfs] [nbdkit PATCH 0/2] bind .zero to more languages
On 01/24/2017 09:16 AM, Richard W.M. Jones wrote:
In Perl, old code to raise an error would look like:
sub pread
{
my $h = shift;
my $count = shift;
my $offset = shift;
my $ret;
read ($FH, $ret, $count, $offset) || die "read: $!"
return $ret;
}
(Note that die does not exit the program, it raises an exception which
is caught and turned into nbdkit_error in the Perl nbdkit plugin).
This would continue to work fine, but new code which cared about the
errno could do this instead:
sub pread
{
my $h = shift;
my $count = shift;
my $offset = shift;
my $ret;
read ($FH, $ret, $count, $offset) || {
nbdkit_set_errno (POSIX::errno ());
die "read: $!"
}
return $ret;
}
Except I can't even figure out how to expose nbdkit_set_error (hmm, I
named it set_error instead of set_errno in my v2 series) to the perl
code. In fact, with just this change to example.pl:
diff --git i/plugins/perl/example.pl w/plugins/perl/example.pl
index fcdac33..64f6de3 100644
--- i/plugins/perl/example.pl
+++ w/plugins/perl/example.pl
@@ -1,4 +1,5 @@
use strict;
+use POSIX ();
# Example Perl plugin.
#
@@ -80,6 +81,8 @@ sub pwrite
my $buf = shift;
my $count = length ($buf);
my $offset = shift;
+ my $err = POSIX::EPERM;
substr ($disk, $offset, $count) = $buf;
+ die "forced write failure";
}
I'm getting this failure:
$ ./src/nbdkit -e foo -fv plugins/perl/.libs/nbdkit-perl-plugin.so \
script=plugins/perl/example.pl
nbdkit: debug: registering plugins/perl/.libs/nbdkit-perl-plugin.so
nbdkit: debug: registered plugins/perl/.libs/nbdkit-perl-plugin.so (name
perl)
nbdkit: debug: plugins/perl/.libs/nbdkit-perl-plugin.so: load
nbdkit: debug: plugins/perl/.libs/nbdkit-perl-plugin.so: config
key=script, value=plugins/perl/example.pl
Can't load module Fcntl, dynamic loading not available in this perl.
(You may need to build a new perl executable which either supports
dynamic loading or has the Fcntl module statically linked into it.)
at /usr/lib64/perl5/POSIX.pm line 17.
Compilation failed in require at /usr/lib64/perl5/POSIX.pm line 17.
BEGIN failed--compilation aborted at /usr/lib64/perl5/POSIX.pm line 17.
Compilation failed in require at plugins/perl/example.pl line 2.
BEGIN failed--compilation aborted at plugins/perl/example.pl line 2.
nbdkit: error: plugins/perl/example.pl: one of the required callbacks
'open', 'get_size' or 'pread' is not defined by this Perl script.
nbdkit requires these callbacks.
So I'm not sure how anyone else is doing anything fancy in an NBD perl
script.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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