Re: Confused by sysread()

2012-04-09 Thread Roger Burton West 
On Mon, Apr 09, 2012 at 02:52:10PM -0700, Yitzchak Scott-Thoennes wrote:

>You've probably switched from perl using stdio to using perlio.

The perl I have certainly has USE_PERLIO set.

>You
>could compile 5.10.1 with usestdio to see if that makes a difference.
>Or you could try a newer perl and see if this is a bug that perhaps
>has been fixed?

Oh dear. I could, but it's rather a slog.

>Which strikes a vague bell...does it help to say: my $data = '';

No. Nor to initialise it to the size of the buffer.

R

Re: Confused by sysread()

2012-04-09 Thread Yitzchak Scott-Thoennes 
On Mon, Apr 9, 2012 at 2:52 PM, Yitzchak Scott-Thoennes
 wrote:
> Which strikes a vague bell...

Sorry, ring bells, strike chords.

Re: Confused by sysread()

2012-04-09 Thread Yitzchak Scott-Thoennes 
On Mon, Apr 9, 2012 at 2:32 PM, Roger Burton West  wrote:
> Under Linux amd64 and Perl 5.10.1, I'm trying to read from a pair of
> devices which will produce data in 16-byte blocks. (I can cat the device
> files - as the same user - and verify that they do this.)
>
> Under Perl 5.8 (and an earlier i386 Linux), this worked. Now sysread()
> is failing with an "Invalid argument".

You've probably switched from perl using stdio to using perlio.  You
could compile 5.10.1 with usestdio to see if that makes a difference.
Or you could try a newer perl and see if this is a bug that perhaps
has been fixed?

Which strikes a vague bell...does it help to say: my $data = '';

Confused by sysread()

2012-04-09 Thread Roger Burton West 
Under Linux amd64 and Perl 5.10.1, I'm trying to read from a pair of
devices which will produce data in 16-byte blocks. (I can cat the device
files - as the same user - and verify that they do this.)

Under Perl 5.8 (and an earlier i386 Linux), this worked. Now sysread()
is failing with an "Invalid argument".

I'm using an IO::Select thus, where @dev contains the device filenames:

my $s=IO::Select->new;
my @fh;
foreach my $device (@dev) {
  my $fh;
  open $fh,'<',$device;
  binmode $fh;
  $s->add(\*$fh);
  push @fh,$fh;
}

while (1) {
  my @ready=$s->can_read(0.5);
  foreach my $fh (@ready) {
my $data;
my $y=sysread $fh,$data,16;
die $! unless defined $y;
# do stuff with $data
  }
}

I can change the open to

sysopen $fh,$device,O_RDONLY;

with no change in the result; if I add O_DIRECT, the @ready list never
gets filled at all.

Have I missed something important somewhere?

Roger