On Tue, 2013-05-28 at 22:10 -0400, Greg Smith wrote:
> I was just thinking of something to run in your test program, not
> another build time check. Just run the new allocation sequence, and
> then check the resulting WAL file for a) correct length, and b) 16K of
> zero bytes. I would like to build some confidence that posix_fallocate
> is operating correctly in this context on at least one platform. My
> experience with Linux handling this class of functions correctly has
> left me skeptical of them working until that's proven to be the case.
As I understand it, you are basically asking if posix_fallocate() works
at all anywhere.
Simple test program attached, which creates two files and fills them:
one by 2048 8KB writes; and another by 1 posix_fallocate of 16MB. Then,
I just cmp the resulting files (and also "ls" them, to make sure they
are 16MB).
Passes on my workstation:
$ uname -a
Linux jdavis 3.5.0-34-generic #55-Ubuntu SMP Thu Jun 6 20:18:19 UTC 2013
x86_64 x86_64 x86_64 GNU/Linux
Regards,
Jeff Davis
#include <fcntl.h>
char buf[8192] = {0};
int main()
{
int i;
int fda = open("/tmp/afile", O_CREAT | O_EXCL | O_WRONLY, 0600);
int fdb = open("/tmp/bfile", O_CREAT | O_EXCL | O_WRONLY, 0600);
for(i = 0; i < 2048; i++)
{
write(fda, buf, 8192);
}
posix_fallocate(fdb, 0, 16*1024*1024);
close(fda);
close(fdb);
return 0;
}
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