Re: O_DIRECT foolish question

[Chris Wedgwood <cw@f00f.org>]

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On Wed, Feb 12, 2003 at 06:33:23PM -0500, Bruno Diniz de Paula wrote:

> But your code doesn't use O_DIRECT:

Sorry, you need to edit it (see my previous email).  A better version
(appended) gives the following results.

cw:3@tapu(cw)$ cp od.c test
cw:3@tapu(cw)$ gcc -Wall od.c
cw:3@tapu(cw)$ ./a.out
read 503 bytes
read 0 bytes

> Let me know whether including O_DIRECT the test worked.

Seems to.  I get 0 the 2nd time about,  presumably this is EOF but
arguably it should return something else.

  --cw

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#define _GNU_SOURCE

#include <unistd.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
    int h;
    int ps;
    char *buf;
    ssize_t n;

    ps = getpagesize();
    if (!(buf = valloc(ps)))
	return 1;
    if ((h = open("test", O_RDONLY|O_DIRECT)) < 0)
	return 1;
    do {
	n = read(h, buf, ps);
	if (n == -1) {
	    perror("read");
	    break;
	}
	printf("read %d bytes\n", n);
    } while(n);

    close(h);

    return 0;
}