On 01/06/2012 02:02 AM, Maik Zumstrull wrote:

Hello list,

I hit a funny BIOS bug the other day where the BIOS suddenly sets a
HPA on a random hard disk, leaving only the first 33 MB accessible.
That disk had one device of a multi-device btrfs on it in my case.
(With dm-crypt/LUKS in between, no partitioning or LVM.)

The reason I'm writing to you is that btrfs apparently didn't care at
all. It didn't complain, and it certainly didn't consider "Uhm, maybe
I should stop writing to a file system that mostly doesn't exist
anymore." The only errors I saw in dmesg were from the lower block
device level: someone trying to read or write beyond the end of a
device. An error btrfs apparently didn't mind. It took me a while to
figure out what had happened, during which time btrfsck and the btrfs
kernel part worked together to pretty much totally trash the fs. (I'm
still trying a few things, but I'm not hopeful. Hold the default
backup rant, I can in fact recover anything that was on this from
elsewhere, I think.)

So, I think during mount, btrfs should check the reported size of the
block device, and if it's significantly smaller than fs metadata
implies it must be, mount degraded or read-only or not at all. And
mostly, complain. Loudly.

I also notice this, when we "mkfs.btrfs" with a "-b fssize", if "fssize" is
larger than dev size, it will not complain and get "beyond the end" errors.

so maybe we limit the mkfs size:

diff --git a/mkfs.c b/mkfs.c
index e3ced19..3ac8525 100644
--- a/mkfs.c
+++ b/mkfs.c

@@ -1282,6 +1282,8 @@ int main(int ac, char **av)
 		ret = btrfs_prepare_device(fd, file, zero_end, &dev_block_count, &mixed);
 		if (block_count == 0)
 			block_count = dev_block_count;
+		if (block_count > dev_block_count);
+			block_count = dev_block_count;
 	} else {
 		ac = 0;
 		file = av[optind++];

thanks,
liubo

This was on Debian's linux-image-3.1.0-1-amd6 at version 3.1.6-1.
Other ways this could happen than HPA are LVM or partitioning.


Maik
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