Bug#570603: libc6: fallocate and posix_fallocate do weird system calls

[Drake Wilson <drake@begriffli.ch>]

Quoth Aurelien Jarno <aurelien@aurel32.net>, on 2010-02-20 11:38:22 +0100:
> On Fri, Feb 19, 2010 at 08:35:59PM -0600, Drake Wilson wrote:
> > Two C source files are attached.  One of them uses Linux fallocate()
> 
> They are not.

D'oh.  Sorry!  *brown paper bag*

Let's try that again, then.  *attach*

> Your filesystem does not support fallocate, so the glibc is emulating it
> with a pwrite.

That makes a certain amount of sense in this context; I originally
assumed I couldn't trust the return value of the syscall due to the
strange parameters (and didn't think ext2 might not have fallocate).

> Reassigning.

Thank you for the attention, and sorry for the initial incorrectness.

   ---> Drake Wilson

#define _GNU_SOURCE
#include <unistd.h>
#include <fcntl.h>

int 
main(int argc, char *argv[])
{
	int const fd = open("file", O_WRONLY | O_CREAT | O_TRUNC, 0666);
	if (fd == -1) return 1;
	int const err = fallocate(fd, 0, 0, (off_t)(1 << 20));
	if (err == -1) return 1;
	return 0;
}

#define _XOPEN_SOURCE 600
#include <unistd.h>
#include <fcntl.h>

int 
main(int argc, char *argv[])
{
	int const fd = open("file", O_WRONLY | O_CREAT | O_TRUNC, 0666);
	if (fd == -1) return 1;
	int const err = posix_fallocate(fd, 0, (off_t)(1 << 20));
	if (err == -1) return 1;
	return 0;
}