From: Roger Pack <rogerpack2005@...>
Date: 2009-01-29T05:27:13+09:00
Subject: Errno::ENOMEM reading a device in Ruby, not in Java though

Question on how to avoid an Errno::ENOMEM

Currently if I open a tape device from my machine [/dev/st2]
in ruby reading the second file from it results in:

read.rb:2:in `read': Cannot allocate memory - /dev/st2 (Errno::ENOMEM)
        from read.rb:2

Java to do the same works, however.

the "cat" command [i.e. cat </dev/st2] also fails with "Not enough
memory"

Here is an strace of the two:

ruby:

open("/dev/st2", O_RDONLY)              = 3
fstat(3, {st_mode=S_IFCHR|0660, st_rdev=makedev(9, 2), ...}) = 0
fstat(3, {st_mode=S_IFCHR|0660, st_rdev=makedev(9, 2), ...}) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0x7fff5721d900) = -1 EINVAL
(Invalid argument)
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
= 0x2b5b53902000
read(3, 0x2b5b53902000, 4096)           = -1 ENOMEM (Cannot allocate
memory)


java:

[pid 25476] open("/dev/nst2", O_RDONLY) = 4
[pid 25476] fstat(4, {st_mode=S_IFCHR|0660, st_rdev=makedev(9, 130),
...}) = 0
[pid 25476] mprotect(0x2aab3409b000, 65536, PROT_READ|PROT_WRITE) = 0
[pid 25476] read(4, "<familysearch-format>\n<type name"..., 65536) = 116

Anybody know if the difference between mmap and mprotect might be
causing this?
Thanks!
-=r
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