Re: Compatible fstat()

[Bill Davidsen <davidsen@tmr.com>]

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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