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Subject[PATCH] sysinfo fix for 2.2.x binary compatability
On Mon Aug 21, 2000 at 11:37:36AM -0600, Erik Andersen wrote:
> >
> > (More detail: for a sum of n terms, it breaks (for example) for equal
> > terms between max/(n-1) as lower and 2*max/n as upper bound. For n=2, this
> > is empty; for n=3, it's between 1/2*max and 2/3*max, for n=4 it'd be
> > between 1/3*max and 1/2*max, and so on.)
>
> Sigh. And it seemed like such a good heuristic at the time. I even spent 5
> whole minutes trying to find cases that broke it. Missed that one. Oh well.
> Guess I'll have to check for overflow the hard way... Patch soon follows,

This updated patch now correctly checks for overflow, where the previous
patch missed some cases,

-Erik

--
Erik B. Andersen email: andersee@debian.org
--This message was written using 73% post-consumer electrons--



--- linux-2.4.0-test6.virgin/kernel/info.c Mon Aug 23 12:15:53 1999
+++ linux/kernel/info.c Mon Aug 21 11:03:14 2000
@@ -32,6 +32,42 @@
si_meminfo(&val);
si_swapinfo(&val);

+ {
+ /* If the sum of all the available memory (i.e. ram + swap +
+ * highmem) is less then can be stored in a 32 bit unsigned long
+ * then we can be binary compatable with 2.2.x kernels. If not,
+ * well, who cares since in that case 2.2.x was broken anyways...
+ *
+ * -Erik Andersen <andersee@debian.org> */
+
+ unsigned long mem_total = val.totalram + val.totalswap;
+ if ( !(mem_total < val.totalram || mem_total < val.totalswap)) {
+ unsigned long mem_total2 = mem_total + val.totalhigh;
+ if (!(mem_total2 < mem_total || mem_total2 < val.totalhigh))
+ {
+ /* If mem_total did not overflow. Divide all memory values by
+ * mem_unit and set mem_unit=1. This leaves things compatable with
+ * 2.2.x, and also retains compatability with earlier 2.4.x
+ * kernels... */
+
+ int bitcount = 0;
+ while (val.mem_unit > 1)
+ {
+ bitcount++;
+ val.mem_unit >>= 1;
+ }
+ val.totalram <<= bitcount;
+ val.freeram <<= bitcount;
+ val.sharedram <<= bitcount;
+ val.bufferram <<= bitcount;
+ val.totalswap <<= bitcount;
+ val.freeswap <<= bitcount;
+ val.totalhigh <<= bitcount;
+ val.freehigh <<= bitcount;
+ }
+ }
+ }
+
if (copy_to_user(info, &val, sizeof(struct sysinfo)))
return -EFAULT;
return 0;
-
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