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SubjectRe: Compatible fstat()
Parag Warudkar wrote:

>
> On Nov 8, 2005, at 5:57 PM, Bill Davidsen wrote:
>
>> Parag Warudkar wrote:
>>
>>> On Nov 8, 2005, at 2:39 PM, Bob Copeland wrote:
>>>
>>>> Isn't this just because the device size is > 2**32? What if you
>>>> use fseeko(3)
>>>> and #define _FILE_OFFSET_BITS 64?
>>>>
>>> Yep. I got it to return the correct hard disk size (17Gb) using
>>> lseek64 and
>>> #define _LARGEFILE64_SOURCE
>>> #define _FILE_OFFSET_BITS 64
>>> Here is what I did
>>> -------------------------------------------------
>>> #define _LARGEFILE64_SOURCE
>>> #define _FILE_OFFSET_BITS 64
>>> #include <stdio.h>
>>> #include <unistd.h>
>>> #include <fcntl.h>
>>> int main()
>>> {
>>> int f;
>>> off64_t off=0;
>>
>> Why is this initialized?
>>
>>> f = open("/dev/hda", O_RDONLY );
>>> if(f <= 0){
>>> perror("open");
>>> exit(0);
>>> }
>>> off = lseek64(f, 0, SEEK_SET);
>>
>> Why do this? it always returns zero.
>>
>>> off = lseek64(f, 0, SEEK_END);
>>> perror("llseek");
>>> printf ("Size %lld\n", off);
>>> close(f);
>>> return 0;
>>> }
>>
>> RETURN VALUE
>> Upon successful completion, lseek returns the resulting offset
>> location as measured in bytes from the beginning of the file.
>> Otherwise, a value of (off_t)-1 is returned and errno is
>> set to indicate the error.
>>
>
> You took it a little too seriously! It was from the scribble-and-
> shuffle-till-it-works department ;) Sole purpose was to figure out a
> way to print the disk size from the device - some how that is!
>
> But thanks for pointing out anyway - it doesn't hurt to be correct no
> matter what the purpose is.

You could look at how blockdev does it, the --getss (sector size) and
--getsize (size in sectors) seem to work, based on trying it on a total
of two machines ;-) Even gives correct size for software RAID arrays!

--
bill davidsen <davidsen@tmr.com>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979

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