Message-ID: <428230C2.5050406@ocre.cea.fr>
Date: Wed, 11 May 2005 18:20:18 +0200
From: Aurelien Degremont - Stagiaire <degremont@ocre.cea.fr>
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To: linux-xfs@oss.sgi.com, Dean Roehrich <roehrich@sgi.com>
Subject: [DMAPI] code error in dm_ip_to_handle()
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Hello,

I'm still working on DMAPI code and I found a problem in 
dm_ip_to_handle() function. In fact, the problem is not specific to this 
function, I just found it here.

To sum up, I found, in the XFS+DMAPI code, along all the different 
calls, you successively cast some structures and recopy data without 
verifying their content. With XFS, all is ok because 2 errors fix each 
others, but, when i try adding dmapi support to ext3, the problem appears.

In order to create a dmapi handle, you must call dm_ip_to_handle().
This function will fill a dm_handle_t structure. The data recopied came 
from a dm_fsfid structure which do not have the same fields.

ex: memcpy( &[DM_HANDLE_T], &[DM_FSID_T], ...)

This copy the content of the len field without errors.
**But the first byte of the fid_data buffer will be recopied in the 
padding field (dm_fid_pad) of the dm_fid structure !** (which is not 
what is expected)
When DMAPI will try to extract the inode number, it will be wrong !

This code works correctly with XFS because XFS uses the same kind of 
structure as DMAPI, and so, when the datas are copied, the padding is ok.
XFS will copied the data from :

xfs_fid2_t --> fid_t -//pad error//-> dm_fsfid_t -//pad error//-> dm_fid_t

Their 2 errors with byte alignement when data are cast and copied, but 
the first is the opposite of the second, so the data are correct at the end.

This is not true when you correctly fill the dm_fsfid_t structure :)

________________________________________________________
#define MAXDMFSFIDSZ	46

typedef struct dm_fsfid {
	__u16		fid_len;		/* length of data in bytes */
	unsigned char	fid_data[MAXDMFSFIDSZ];	/* data (fid_len worth)  */
} dm_fsfid_t;

struct dm_fid {
	__u16	dm_fid_len;		/* length of remainder	*/
	__u16	dm_fid_pad;
	__u32	dm_fid_gen;		/* generation number	*/
	__u64	dm_fid_ino;		/* 64 bits inode number */
};
typedef struct dm_fid dm_fid_t;


struct dm_handle {
	union {
		__s64	    align;	/* force alignment of ha_fid	 */
		dm_fsid_t  _ha_fsid;	/* unique file system identifier */
	} ha_u;
	dm_fid_t	ha_fid;		/* file system specific file ID	 */
};
typedef struct dm_handle dm_handle_t;
________________________________________________________


Aurélien