Write attempt to file in ZFS snapshot dir causes panic

[krad]

2009/10/19 Carl Chave <online at chave.us>

> I'm new to FreeBSD.  Been experimenting with 8.0-RC1 and zfs in a VM.
> Really haven't even installed it yet, just getting familiar with zfs
> usage from the fixit environment.  I experienced some strange behavior
> and was wondering if this would warrant a bug report:
>
> 1. load zfs from bootloader prompt and then boot.
> 2. enter fixit environment.
> 3. import zpool (in this case a 2 disk vmware mirror named sodpool)
> 4. cd to previously created snapshot at sodpool/test/myfs/.zfs/snapshot/one
> 5. attempting to create a new file here results in:
>
> Fixit# echo hello > hello.txt
> cannot create hello.txt: Read-only file system
>
> 6. That seems like the desired response.  Next, attempt to modify a
> file that already exists in the snapshot:
>
> Fixit# echo hello >> test.txt
> panic: dirtying snapshot!
>
> I know I'm not supposed to be modifying a snapshot file, but a panic
> doesn't seem like the best response to this situation.
>
> I'm using DVD iso named 8.0-RC1-amd64-dvd1.iso
>
> This bug report has the same panic but the scenario is different:
> http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/138764
>
> Is there someplace else I should check for existing issues?
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I dont see these issues

$ echo i > o
bash: o: Read-only file system
$ pwd
/usr/local/.zfs/snapshot/20090816
$ echo i >> o
bash: o: Read-only file system
$ uname -a
FreeBSD X 8.0-RC1 FreeBSD 8.0-RC1 #71: Sun Oct 18 07:05:25 BST 2009
root at X:/usr/obj/usr/src/sys/me  amd64