JFFS2/xattr problems.

[KaiGai Kohei]

Hi, David.

I fixed the problem when xdatum/xref was removed, and so on.

[1/2] jffs2-xattr-v6-01-delete_marker.patch
[2/2] jffs2-xattr-v6-02-fix_posixacl_bug.patch

This correction uses 'delete marker' instead of filling an
existing node by 0xff. It is written when we remvoe xdatum/xref.

Any nodes indicates xdatum/xref includes 'delete marker' are
chained with xd->node or ref->node.
# In the previous implementation, xd->node and ref->node have
# only one node.
Then the garbage collector tries to remove those nodes except
the latest one.

If the latest one is delete marker and any other nodes are not chained
this list, the garbage collector remove the delete marker and in-memory
object (xattr_datum, xattr_ref).
# In previous implementation, deletion of nodes and in-memory objects
# are done immediately

- A xdatum with 'version' equals 0xffffffff means delete marker.
- A xref with odd-numbered 'xseqno' means delete marker.
  It increases 4-byte additional consumption per xref. :(

And the second patch fixes posix-acl bug when we try to replace
null-xattr by null-acl.
Those have been commited into jffs2-xattr-2.6.git.

Thanks,

KaiGai Kohei wrote:
> Hello, David.
> 
> David Woodhouse wrote:
>> I created a user xattr on JFFS2, then attempted to remove it. On NAND
>> flash I get the following BUG():
>>
>> jffs2_flash_writev(): Non-contiguous write to 004ca000
>> wbuf was previously 004ca000-004ca040
>> ------------[ cut here ]------------
>> kernel BUG at /root/jffs2/wbuf.c:672!
>>
>> Call Trace:
>>  [<c8222aad>] jffs2_flash_writev+0x616/0x6ac [jffs2]
>>  [<c823eadb>] nand_read_ecc+0x29/0x2f [nand]     [<c823eadb>] nand_read_ecc+0x29/0x2f [nand]
>>  [<c8221a6a>] jffs2_flash_read+0x8a/0x22b [jffs2]     [<c8222b8b>] jffs2_flash_write+0x48/0x51 [jffs2]
>>  [<c822364d>] delete_xattr_datum_node+0xcc/0x144 [jffs2]     [<c8223dea>] delete_xattr_datum+0x2c/0x3c [jffs2]
>>  [<c8223ed2>] delete_xattr_ref+0x32/0x3b [jffs2]     [<c8224e37>] do_jffs2_setxattr+0x1a9/0x5aa [jffs2]
>>  [<c01c1462>] _atomic_dec_and_lock+0x22/0x2c     [<c82254fc>] jffs2_user_setxattr+0x3c/0x47 [jffs2]
>>  [<c016e9e8>] generic_removexattr+0x37/0x3d     [<c016ef78>] vfs_removexattr+0x78/0xc8
>>
>> What is delete_xattr_datum_node() trying to do? It seems to be writing
>> for a second time to an area of flash which has _already_ been written.
>> You can't do that.
> 
> delete_xattr_datum_node() try to write invalid data to ensure the target
> node was already deleted. I was worried about that a xdatum already removed
> may be reused as a effective xdatum on next mounting.
> But it's purely design problem that should be changed.
> 
> Alternatively, I plan to write a delete marker on new node allocated by
> jffs2_reserve_space() when xdatum is removed.
> I intend to be dealt with a xdatum with 0xffffffff of version number
> as a delete marker for xdatum. This node will be ignored on next mounting.
> 
> There is a same issue on deletion of xattr_ref, I also plan to implement
> with same method.
> 
> Some days will be necessary to change it.
> Would you wait for a while?
> 
>> Also, just 'cp -av /lib/libc.so.6 /mnt/jffs2' is failing to set the
>> POSIX ACL, with -EINVAL. This happens because posix_acl_equiv_mode()
>> returns zero, because the ACL is entirely equivalent to normal modes. So
>> the 'value' passed to do_jffs2_setxattr() is NULL, which should _delete_
>> the corresponding xattr.
>>
>> But because the xattr is not found, the code returns -EINVAL. Shouldn't
>> that error be -ENOATTR? And shouldn't the ACL code then convert it to a
>> more appropriate return value?
> 
> I agree, I'll fix it.
> 
> Thanks,
-- 
Open Source Software Promotion Center, NEC
KaiGai Kohei <kaigai at ak.jp.nec.com>
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