klibc - Jul 2004 - getpagesize / libsysfs broken with 0.148

On Thu, 2004-07-15 at 01:51, Hannes Reinecke wrote:
> Hi all,
> 
> the implementation of getpagesize() is broken in klibc.
> 
> klibc uses sysinfo.mem_unit, which linux interpretes as the memory unit 
> all other memory values returned are to be multiplied with.
> So it's perfectly ok for the linux sysinfo() to return a mem_unit of 
> '1', which is does if the memory available for this machine fits
into
> the counter.
> For the unbelievers, have a look in kernel/timer.c:sys_sysinfo().
> 
> As a quick hack I've added a check for mem_unit==1 and reset the 
> page_size to 4096 on those cases.
> 
> Naturally, this is not the right fix. The right fix would be to get the 
> values from the kernel headers and/or some magic juju for those machines 
> with variable pagesize.
> 
> It probably would not have been noticed, but as libsysfs insists on 
> doing all reads from sysfs attributes with a length of pagesize, the 
> failures were ... interesting.

Libsysfs reads with length of pagesize because that was a sysfs
limitation. Has sysfs changed? 

There use to be an ifdef klibc around the getpagesize() call but that
seems to have been removed at some point. 

Thanks, 

Dan



> So in short, udev does _not_ work with klibc until that (or an 
> equivalent) patch is applied.
> 
> Cheers,
> 
> Hannes

Hi all,

the implementation of getpagesize() is broken in klibc.

klibc uses sysinfo.mem_unit, which linux interpretes as the memory unit 
all other memory values returned are to be multiplied with.
So it's perfectly ok for the linux sysinfo() to return a mem_unit of 
'1', which is does if the memory available for this machine fits into 
the counter.
For the unbelievers, have a look in kernel/timer.c:sys_sysinfo().

As a quick hack I've added a check for mem_unit==1 and reset the 
page_size to 4096 on those cases.

Naturally, this is not the right fix. The right fix would be to get the 
values from the kernel headers and/or some magic juju for those machines 
with variable pagesize.

It probably would not have been noticed, but as libsysfs insists on 
doing all reads from sysfs attributes with a length of pagesize, the 
failures were ... interesting.

So in short, udev does _not_ work with klibc until that (or an 
equivalent) patch is applied.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke			hare@suse.de
SuSE Linux AG				S390 & zSeries
Maxfeldstra?e 5				+49 911 74053 688
90409 N?rnberg				http://www.suse.de
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Hannes Reinecke wrote:
 >
> Hi all,
> 
> the implementation of getpagesize() is broken in klibc.
> 
> klibc uses sysinfo.mem_unit, which linux interpretes as the memory unit 
> all other memory values returned are to be multiplied with.
> So it's perfectly ok for the linux sysinfo() to return a mem_unit of 
> '1', which is does if the memory available for this machine fits
into
> the counter.
> For the unbelievers, have a look in kernel/timer.c:sys_sysinfo().
> 
> As a quick hack I've added a check for mem_unit==1 and reset the 
> page_size to 4096 on those cases.
> 
*SIGH* So much for the claim that there actually existed a sane way to 
get the page size across platforms.  This is particularly nasty because 
of the definition of mmap2().

The kernel headers don't work very well since page size is a 
kernel-compile-time option on some platforms, e.g. MIPS, and dynamic on 
some platforms.

	-hpa