Re: Compatible fstat()

[Theodore Ts'o]

On Tue, Nov 08, 2005 at 05:22:44PM +0000, Al Viro wrote:
> On Tue, Nov 08, 2005 at 12:10:25PM -0500, Parag Warudkar wrote:
> > 
> > On Nov 8, 2005, at 10:48 AM, linux-os ((Dick Johnson)) wrote:
> > 
> > >The Linux fstat() doesn't return any information number of blocks,
> > >or the byte-length of a physical hard disk.
> > 
> > I don't think (f)stat returns size and blocks information about a  
> > block device on any UNIX platform.
> > 
> > But I don't know for sure how to get it - perhaps ioctl on the  
> > device? BLKGETSIZE?
> 
> 	fd = open(bdev, O_RDONLY);
> 	lseek(fd, SEEK_END, 0);
> 	size = lseek(fd, SEEK_SET, 0);
> 	close(fd);
> 
> i.e. same as for regular files.  Won't be portable, though...

As I recall, this didn't always work; e2fsprogs falls back to using a
binary search using SEEK_SET to find the device size.  Folks who need
to do this should look at lib/ext2fs/getsize.c in the e2fsprogs
sources; it has ioctl's and other procedures for determining block
device size for Linux, *BSD, MacOSX, as well a generalized binary
search algorithm.

						- Ted

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