return value of lseek(fd, 0, SEEK_CUR) for O_APPEND files

[Martin Sebor <msebor@xxxxxxxxx>]

On the two implementations I've tried lseek(fd, 0, SEEK_CUR) returns
0 for files opened with the O_APPEND bit set. AFAICS, this violates
the requirements that:

  1) open(2): O_APPEND If set, the file offset shall be set to
     the end of the file prior to each write.

  2) lseek(2): "Upon successful completion, the resulting offset,
     as measured in bytes from the beginning of the file, shall be
     returned."

Am I missing something or are these implementations buggy? (E.g.,
does the "prior to each write" part in (1) above mean prior to
the OS writing to the actual file rather than "prior to the
application making the write() call?")

Thanks
Martin

PS Here's a test program along with its output on the two systems:

$ cat t.c && gcc t.c && ./a.out
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>

int main ()
{
    FILE *fp;
    int fd;

    fp = fopen (__FILE__, "a");
    fd = open (__FILE__, O_WRONLY | O_APPEND);

#define PRINT(A)   printf ("%s = %li\n", #A, (A))

    PRINT (lseek (fileno (fp), 0, SEEK_CUR));
    PRINT (ftell (fp));
    PRINT (lseek (fd, 0, SEEK_CUR));
}

lseek (fileno (fp), 0, SEEK_CUR) = 341
ftell (fp) = 341
lseek (fd, 0, SEEK_CUR) = 0