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SubjectRe: Busy on BLKFLSBUF w/initrd
On Thu, 24 May 2001, Maciek Nowacki wrote:

> Problem seems to be solved. Here is what I did, for anyone who is interested
> in using a loopback file on a local disk as root:
[snip recipe]
> This method depends on the change_root() mechanism which I had assumed is
> becoming obsolete. It works, and there is no need to mess with
> /proc/sys/kernel/real_root_dev if the root is specified on the command line.
> Trying to use only pivot_root did not work as /dev/rd/0 could never be
> flushed (see previous messages in this thread).

I was having similiar problems a few months back. I was also trying
to pivot_root out of an initial ramdisk and then unmount it. I got it
working, but kept forgetting to post one of the fixes that I found
necessary to make it work when using auto-mounted devfs.

Here it is (exported from BitKeeper, hence the a and b):

diff -Nru a/init/main.c b/init/main.c
--- a/init/main.c Fri May 25 00:31:25 2001
+++ b/init/main.c Fri May 25 00:31:25 2001
@@ -273,6 +273,9 @@
#ifdef CONFIG_NFTL
{ "nftla", 0x5d00 },
#endif
+#ifdef CONFIG_DEVFS_MOUNT
+ { "rd/", 0x0100 },
+#endif
{ NULL, 0 }
};

What this does is make /dev/rd/* parseable by name_to_kdev_t, with
the result that ROOT_DEV gets set correctly in root_dev_setup and
the initrd logic at the bottom of do_basic_setup doesn't automatically
trigger the change_root. The same effect can be achieved by setting
real_root_dev in proc in your ramdisk, but since that's not required
for non-devfs ramdisks, it takes some digging for the uninitiated to
figure out why things don't work.
With this fix and the fix for the missing bldev_put in drivers/block/rd.c
(which has been in Alan's tree for ages), the pivot_root instructions
given in the file Documentation/initrd.txt have been working fine for me.

Scott


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Scott Murray email: scott@spiteful.org
http://www.spiteful.org (coming soon) ICQ: 10602428
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