Scott Johnson wrote:
> I'm a little bit confused about how to determine whether Linux is
> installed for CS::Platform::GetPhysicalMemorySize().
> Since Linux/UNIX aren't distinguished at configuration time, I am
> probably going to need to tweak the configure.ac file to make sure it
> does a test for the memory checking functions, and apply the appropriate
> functionality. I was thinking about doing a check for the function
> sysinfo() using AC_CHECK_LIB, but I'm not 100% sure how I would go about
> doing this (I've never written a configure script before). I'm
> wondering if there's a way to have $host_os specify whether true unix
> (e.g. openbsd) or linux (e.g. redhat-linux, ubuntu, etc...) is being
> used. I guess my question is what AC_CANONICAL_HOST actually returns
> inside of $host_os.
There is no need to make a distinction either about the platform type
(Unix, Windows, etc.) nor about the particular flavor of Unix (Linux,
BSD, etc.). Instead, just test for sysinfo() and any other functions the
implementation may need. The test will either succeed or fail. If it
succeeds, then the implementation can utilize the function, else the
implementation should fall back to some other scheme. The csutil/unix
implementation shouldn't care if the platform is Linux (RedHat, Ubuntu,
etc.), BSD, or whatnot. Instead, it merely utilizes whichever
capabilities the configure script determines are present. Consequently,
there is no need to mess with AC_CANONICAL_HOST(), $host_os, etc.
AC_CHECK_LIB() is suitable for checking presence of a function in a
particular library, so it could be used for the sysinfo() check. On the
other hand, CS_CHECK_BUILD() is useful for checking if short code
fragments compile cleanly, and is therefore also suitable for sysinfo().
The configure.ac check for sysinfo() might look like this:
CS_CHECK_BUILD(
[for sysinfo()],
[cs_cv_sysinfo],
[AC_LANG_PROGRAM(
[[#include <sys/sysinfo.h>]],
[struct sysinfo x; sysinfo(&x);])],
[],[],
[CS_HEADER_PROPERTY([CS_HAVE_SYSINFO])])
This check will #define CS_HAVE_SYSINFO in csconfig.h, if the check
succeeds, which your implementation can then check with #ifdef. It is
safe for this configure test to run on non-Linux platforms, such as
Windows, Mac OS X, etc., so there is no need to conditionalize it.
Simply employ the result in your implementation.
Note also that you don't need to distinguish Linux versus other Unix
implementations for your run-time code attempting to retrieve memory
size. For instance, the fallback tests which attempt to query
/proc/meminfo, /dev/kmem, etc. can be made regardless of precise
platform. Just attempt each in turn until one succeeds or they all fail,
in which case you return 0 as an error indicator.
-- ES
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