Re: [PATCH 1/8] Scaling msgmni to the amount of lowmem

From: Michael Kerrisk
Date: Tue May 20 2008 - 10:28:38 EST


Hello Nadia,

Regarding your:

[PATCH 1/8] Scaling msgmni to the amount of lowmem
http://article.gmane.org/gmane.linux.kernel/637849/
which I see has made its way in 2.6.26-rc

Your patch has the following change:

-#define MSGPOOL (MSGMNI*MSGMNB/1024) /* size in kilobytes of message pool */
+#define MSGPOOL (MSGMNI * MSGMNB) /* size in bytes of message pool */

Since this constitutes a kernel-userland interface change, so please
do CC me, so that I can change the man pages if needed.

The man page (http://www.kernel.org/doc/man-pages/online/pages/man2/msgctl.2.html)
does indeed say that msgpool is "unused". But that meant "unused by
the kernel" (sorry -- I probably should have worded that text better).
And, as you spotted, the page also wrongly said the value is in
bytes.

However, making this change affects the ABI. A userspace application
that was previously using msgctl(IPC_INFO) to retrieve the msgpool
field will be affected by the factor-of-1024 change. I strongly
suspect that there no such applications, or certainly none that care
(since this value is unused by the kernel). But was there a reason
for making this change, aside from the fact that the code and the man
page didn't agree?

Cheers,

Michael

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/