kern/164793: 'write' system call violates POSIX standard

[Nicolas Bourdaud]

>Number:         164793
>Category:       kern
>Synopsis:       'write' system call violates POSIX standard
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Feb 05 11:50:08 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Nicolas Bourdaud
>Release:        FreeBSD 9.0-RELEASE
>Organization:
>Environment:
GNU/kFreeBSD debian-bsd-amd64 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Tue Jan  3 
07:46:30 UTC 2012     r...@farrell.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC 
x86_64 amd64 Intel(R) Core(TM)2 Duo CPU     E7500  @ 2.93GHz GNU/kFreeBSD
>Description:
When a write() cannot transfer as many bytes as requested (because of a file
limit), it fails instead of transferring as many bytes as there is room to
write.

This is a violation of the POSIX standard:
http://pubs.opengroup.org/onlinepubs/007904975/functions/write.html
>How-To-Repeat:
fsize-lim.c.txt (attached) illustrates the problem. With a freebsd kernel, the
output is:
failed when adding 27 bytes after 59994 bytes (error: File too large)

The expected output (like with a linux kernel) should be:
added 6 bytes instead of 27 bytes after 59994 bytes
failed when adding 27 bytes after 60000 bytes (error: File too large)
>Fix:


Patch attached with submission follows:

#include <unistd.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <signal.h>
#include <errno.h>
#include <string.h>

#define TARGETSIZE      80000
#define LIMSIZE         60000
#define PATTSIZE        27


int main(void)
{
        struct rlimit lim;
        int fd;
        ssize_t retc;
        size_t count = 0;
        const char pattern[PATTSIZE] = "Hello world!";
        
        signal(SIGXFSZ, SIG_IGN);
        lim.rlim_cur = LIMSIZE; 
        setrlimit(RLIMIT_FSIZE, &lim);

        fd = open("result.txt", O_WRONLY|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR);

        while (count < TARGETSIZE) {
                retc = write(fd, pattern, PATTSIZE);

                if (retc < PATTSIZE && retc > 0)
                        fprintf(stderr,
                                "added %zi bytes instead of %u bytes after %zu 
bytes\n",
                                retc, PATTSIZE, count);
                else if (retc < 0) {
                        fprintf(stderr,
                                "failed when adding %u bytes after %zu bytes 
(error: %s)\n",
                                PATTSIZE, count, strerror(errno));
                        break;
                }
                count += retc;
        }

        close(fd);

        return 0;
}


>Release-Note:
>Audit-Trail:
>Unformatted:
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