Dereferencing pointers returned by syscall

[tad.bochan]

Hi,

I'm using 'syscall' in ruby to access the 'mmap' function in Unix (HPUX),
to try to read/write a memory-mapped file.
The 'mmap' function returns a pointer to the mapped file.
I can't figure out how I am supposed to be able to use
this pointer to access the data from ruby.

PROT-NONE = 0
PROT-USER = 0
PROT-READ = 1
PROT-WRITE = 2
MAP-SHARED = 1
prot=PROT_READ | PROT_WRITE
flags=MAP_SHARED
len=1024
ofs=0
mmfptr=syscall(71, 0, prot, flags, filedes, ofs)

mmfptr is now a pointer to a 1024 byte structure.

How can I get ruby to access this structure ?

Regards,

Tad. (ruby,perl,unix newbie)





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[Florian Gross]

Hi,
Moin!

I'm using 'syscall' in ruby to access the 'mmap' function in Unix (HPUX),
to try to read/write a memory-mapped file.
The 'mmap' function returns a pointer to the mapped file.
I can't figure out how I am supposed to be able to use
this pointer to access the data from ruby.

Have a look at Ruby/DL which is part of Standard Ruby. With
DL::Importable you can create a struct like this:

Foo = struct [
"long foo",
"int bar",
...
]

And later you can do Foo.new(DL:trData.new(ptr)).

Regards,
Florian Gross

 

[nobu.nokada]

Hi,

At Fri, 27 Aug 2004 04:05:35 +0900,
Florian Gross wrote in [ruby-talk:110570]:

And later you can do Foo.new(DL:trData.new(ptr)).

munmap(2) takes two arguments, but DL:trData passes to its
free functions just one argument.