vmsplice complains bad address

[Yi Yang <yang.y.yi@gmail.com>]

Hi, Jens

When I tested vmsplice syscall, it always complains bad address, I don't
understand why, does vmsplice have a special reqiurement for address
alignment?

The following file is a test program which is extracted from your patch
and modified in order to adapt to the latest interface. its output is:

getpagesize = 4096
page size: 4096 bytes
vmsplice: Bad address
here: len = 4096, written = -1


/*
* Use vmsplice to fill some user memory into a pipe. vmsplice writes
* to stdout, so that must be a pipe.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/poll.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <error.h>
#include <errno.h>

//#include "splice.h"
#if defined(__i386__)
#define __NR_splice 313
#define __NR_tee 315
#define __NR_vmsplice 316
#elif defined(__x86_64__)
#define __NR_splice 275
#define __NR_tee 276
#define __NR_vmsplice 277
#elif defined(__powerpc__) || defined(__powerpc64__)
#define __NR_splice 283
#define __NR_tee 284
#define __NR_vmsplice 285
#else
#error unsupported arch
#endif

#define SPLICE_SIZE 4096
#ifndef F_SETPSZ
#define F_SETPSZ 15 /* for pipes. */
#define F_GETPSZ 16 /* for pipes. */
#endif

#define ALIGN_BUF

#ifdef ALIGN_BUF
#define ALIGN_MASK (65535) /* 64k-1, should just be PAGE_SIZE - 1 */
#define ALIGN(buf) (void *) (((unsigned long) (buf) + ALIGN_MASK) &
~ALIGN_MASK)
#else
#define ALIGN_MASK (0)
#define ALIGN(buf) (buf)
#endif

#define min(a,b) (((a)>(b))?(b):(a))

static inline int xerror(const char * str)
{
int err = errno;
perror(str);
return err;
}

static inline long vmsplice(int fd, const struct iovec *iov,
unsigned long nr_segs, unsigned int flags)
{
return syscall(__NR_vmsplice, fd, iov, nr_segs, flags);
}

int do_vmsplice(int fd, void *buffer, int len)
{
struct pollfd pfd = { .fd = fd, .events = POLLOUT, };
int written;
struct iovec v;

v.iov_base = buffer;
v.iov_len = len;

while (len) {
/*
* in a real app you'd be more clever with poll of course,
* here we are basically just blocking on output room and
* not using the free time for anything interesting.
*/
if (poll(&pfd, 1, -1) < 0)
return xerror("poll");

written = vmsplice(fd, &v, 1, 0);
printf("here: len = %d, written = %d\n", len, written);

if (written <= 0)
return xerror("vmsplice");
printf("dajdsajkdskj\n");
fprintf(stderr, "written len = %d\n", written);

len -= written;
}

return 0;
}

int main(int argc, char *argv[])
{
unsigned char *buffer;
struct stat sb;
long page_size;
int i, ret;

if (fstat(STDOUT_FILENO, &sb) < 0)
return xerror("stat");
if (!S_ISFIFO(sb.st_mode)) {
fprintf(stderr, "stdout must be a pipe\n");
return 1;
}

page_size = sysconf(_SC_PAGESIZE);
if (page_size < 0)
return xerror("_SC_PAGESIZE");

fprintf(stderr, "getpagesize = %d\n", getpagesize());
fprintf(stderr, "page size: %d bytes\n", page_size);

buffer = malloc(2 * 65536);
buffer[0]='A';
for (i = 1; i < 2 * SPLICE_SIZE; i++)
buffer[i] = (i & 0xff);

do {
/*
* vmsplice the first half of the buffer into the pipe
*/
if (do_vmsplice(STDOUT_FILENO, buffer, SPLICE_SIZE))
break;

/*
* first half is now in pipe, but we don't quite know when
* we can reuse it.
*/

/*
* vmsplice second half
*/
//if (do_vmsplice(STDOUT_FILENO, buffer + SPLICE_SIZE, SPLICE_SIZE))
// break;

/*
* We still don't know when we can reuse the second half of
* the buffer, but we do now know that all parts of the first
* half have been consumed from the pipe - so we can reuse that.
*/
} while (0);

free(buffer);

return 0;
}