Writes to Hard Disk Going Beyond Capacity

[Patrick Donnelly]

On Sat, Jul 10, 2010 at 2:38 PM, C. P. Ghost <cpghost at cordula.ws> wrote:
>> Are you aware of short writes?
>>
>> static int write_buf (int fd, const char *buf, size_t s)
>> {
>>  ssize_t r = write(fd, buf, s);
>>  if (r == -1)
>>    fprintf(stderr, "write error: %s\n", strerror(errno));
>>  return r >= 0;
>> }
>>
>> What if write(2) returns less than s, but not -1?
>
> Or, to be more precise, is it possible that write(2) returns 0 for
> some reason, perhaps because the device isn't ready and can't
> accept more data, so it says that it wrote 0 bytes, but that you
> are free to try again?
>
> On Solaris, the write(2) man page says:
>
>  If a write() requests that more bytes be written than there is room
>  for—for example, if the write would exceed the process file size
>  limit (see getrlimit(2) and ulimit(2)), the system file size limit,
>  or the free space on the device—only as many bytes as there is room
>  for will be written. For example, suppose there is space for 20
>  bytes more in a file before reaching a limit. A write() of 512-bytes
>  returns 20. The next write() of a non-zero number of bytes gives a
>  failure return (except as noted for pipes and FIFO below).
>
> http://docs.sun.com/app/docs/doc/816-5167/write-2?l=en&n=1&a=view
>
> Have you tried your program on [Open]Solaris too? What happens there?
> Perhaps our write(2) isn't entirely IEEE Std 1003.1 compliant? Because
> write(2) there says:
>
>  If a write() requests that more bytes be written than there is room
>  for (for example, [XSI] [Option Start] the process' file size limit
>  or [Option End] the physical end of a medium), only as many bytes as
>  there is room for shall be written. For example, suppose there is
>  space for 20 bytes more in a file before reaching a limit. A write
>  of 512 bytes will return 20. The next write of a non-zero number of
>  bytes would give a failure return (except as noted below). (...)
>
> http://www.opengroup.org/onlinepubs/000095399/functions/write.html
>
> Hmmm... any C/POSIX standards lawyers/specialists here?

write returning 0 appears to be the problem. That is indeed strange
and I would guess it may be a bug?

-- 
- Patrick Donnelly