bin/48183: Example in man write(2) causes endless loop

[manuel%bsdstammtisch.at@localhost]

>Number:         48183
>Category:       bin
>Synopsis:       Example in man write(2) causes endless loop
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          doc-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 04 23:30:00 +0000 2013
>Originator:     Manuel Wiesinger
>Release:        6.99.23
>Organization:
>Environment:
NetBSD scampi 6.99.23 NetBSD 6.99.23 (GENERIC) #0: Fri Jul 19 21:47:43 CEST 
2013  manuel@scampi:/usr/obj/sys/arch/amd64/compile/GENERIC amd64

>Description:
The manpage of pread says:

Proper loops should use
while ((nr = write(fd, buf, sizeof(buf))) != -1 && nr != 0)

which is clearly an endless loop. Say nr = 512 and the write is successful, 
then 512 != -1 && n1 !=0  is true.
>How-To-Repeat:
Compile this C program:

#include <fcntl.h>

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>


int
main()
{
    off_t blk, new_blk;
    ssize_t w;
    char buf[] = "heydo";

    int fd = open("/tmp/test", O_WRONLY | O_CREAT);

    while ((w = write(fd, buf, sizeof(buf))) != -1 && w != 0)
        printf("w: %ld\n", w);

    return 1;
}

>Fix:
Suggest something like the following.

When zero bytes have been written, or the write has failed error handling is 
necessary.

#include <fcntl.h>

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>


int
main()
{
    off_t blk, new_blk;
    ssize_t w;
    char buf[] = "heydo";

    int fd = open("/tmp/test", O_WRONLY | O_CREAT);

    while ((w = write(fd, buf, sizeof(buf))) != sizeof(buf)) {
        if(w == 0 || w == -1) 
            errx(EXIT_FAILURE, "could not write\n");
    }   

    return 1;
}