I have recently posted a patch to remove the small ipc message queue
limitations from the linux kernel. As part of those changes the kernel
msqid_ds structure had to be altered. Specifically, the msg_cbytes and
msg_qbyte parameters were from changed from unsigned short to unsigned
int's to remove the 64K restriction imposed. This changes aren't in the
kernel images yet, but are in Alan Cox's current patch set (patch-2.1.131-ac5).
The kernel will now pass back the "large" msg_cbytes and msg_qbytes info
in the fields that were formerly __wwait, and __rwait -- structures used
only in the kernel. Only the msgctl function is effected, since that is
the only one that passes the msqid_ds structure.
I have prepared some libc changes to allow the use of the new fields on
kernels that have the large message support. The msg_qbytes and msg_cbytes
fields have been renamed with a __old prefix, and the 32 bit fields have
replaced them. If the underlying kernel at run time does not have the large
message support (ie: old) then the msg_[qc]bytes fields are copied into the
old locations before the syscall.
I am appending the changes I have prepared, but I believe there are a couple
things to be addressed before they could be included into libc, and I wanted
to ask you to take a look at them.
1) I think symbol versioning would be needed for the new msgctl call, since
old libraries and executables linked against glibc 2.0 would expect the
msg_[cq]bytes fields to be at the old offsets, and be only 16 bits wide.
2) In msq.h I have put in two temporary ifdef __alpha__ where a test is needed
to check if the (Linux) platform is 64 bit (ie: alpha, sparc64, ...) -- I
presume that you have a "proper" macro for this in libc. I found
_XBS5_LP64_OFF32 in sysdeps/wordsize-64/bits/environments.h, but I don't
think unistd.h can be included in msq.h without namespace pollution -- correct?
Peeter
-- Peeter Joot peeterj@ca.ibm.comMessage-ID: <714.913185906@peeterj.torolab.ibm.com> Mime-Version: 1.0 Subject: libc support for large message queues (Linux) Content-Type: multipart/mixed; boundary="-"
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