From: Roger Pack <rogerpack2005@...>
Date: 2009-11-17T05:04:20+09:00
Subject: Re: Errno::ENOMEM reading a device in Ruby, not in Java thou


> |irb(main):005:0> a.sysread 64*1024
> |IOError: sysread for buffered IO
...
> rewind it first to clear buffering.

Interesting.  It seems to indeed allow for it.

I was unable to actually test it on a tape devicesince it appears that 
eof? calls a read of size 8192:

read(3, 0x6c9ba90, 8192)                = -1 ENOMEM (Cannot allocate 
memory)

which would be smaller than what I would need [which is ok I can live 
without eof].

Also as a note, it ends up that, with tape drives the trick is to read 
from a device into a buffer that's at least as large as the largest 
"block" of data written onto the tape, or else you'll get ENOMEM.

ex:
write 1000 bytes
File.open('tape_device like /dev/nst2', 'w') do |f| f.syswrite 'a*1000; 
end
now read
File.open('tape_device', 'r') do |f| f.sysread 100; end # fails
File.open('tape_device', 'r') do |f| f.sysread 1000; end # succeeds

Nothing to do with ruby itself, but thought I'd mention it for 
followers.
-r
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