Re: loop device broken in 2.4.6-pre5

Jari Ruusu (jari.ruusu@pp.inet.fi)
Tue, 26 Jun 2001 11:18:47 +0300


This patch fixes the problem. Please consider applying.

--- linux-2.4.6-pre5/drivers/block/loop.c Sat Jun 23 07:52:39 2001
+++ linux/drivers/block/loop.c Tue Jun 26 09:21:47 2001
@@ -653,7 +653,7 @@
bs = 0;
if (blksize_size[MAJOR(lo_device)])
bs = blksize_size[MAJOR(lo_device)][MINOR(lo_device)];
- if (!bs)
+ if (!bs || S_ISREG(inode->i_mode))
bs = BLOCK_SIZE;

set_blocksize(dev, bs);

Jari Ruusu wrote:
> Andries.Brouwer@cwi.nl wrote:
> > From: Jari Ruusu <jari.ruusu@pp.inet.fi>
> >
> > File backed loop device on 4k block size ext2 filesystem:
> >
> > # dd if=/dev/zero of=file1 bs=1024 count=10
> > 10+0 records in
> > 10+0 records out
> > # losetup /dev/loop0 file1
> > # dd if=/dev/zero of=/dev/loop0 bs=1024 count=10 conv=notrunc
> > dd: /dev/loop0: No space left on device
> > 9+0 records in
> > 8+0 records out
> > # tune2fs -l /dev/hda1 2>&1| grep "Block size"
> > Block size: 4096
> > # uname -a
> > Linux debian 2.4.6-pre5 #1 Thu Jun 21 14:27:25 EEST 2001 i686 unknown
> >
> > Stock 2.4.5 and 2.4.5-ac15 don't have this problem.
> >
> > I am not sure there is an error here.
> >
> > The default block size of a loop device is that of the underlying device.
> > There was a kernel bug that was recently fixed, where the block size
> > of a file backed loop device could be essentially random.
> > So, earlier you happened to get blocksize 1024, and you had room for
> > 10 blocks of size 1024.
> > Now you have blocksize 4096, and you have room for 2 blocks of size 4096.
> > There are no fractional blocks at the end of a block device.
>
> Why can't we keep the default at 1024 regardless of what the block size of
> underlying device is. There are some situations where all of loop device
> must be accessed before it is mounted (at which point the block size is set
> to desired value).

Regards,
Jari Ruusu <jari.ruusu@pp.inet.fi>
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