Eddy Zhao wrote:
> Hello Eric:
>
>>
>> Well, the fact that you have 2 arches would have been highly relevant in
>> your first email. ;) Is this the old abi or the new? Guessing old,
>> based on the alignment issues.
>>
>
> ARM compiler is producing eabi. The problem lies in: "long long" on arm
> is 8 bytes aligned, on x86 is 4 bytes aligned. So 4 more bytes are
> padded before xfs_inode_log_format::ilf_ino on arm.
A tool that can be very helpful here is "pahole" found in the dwarves
package:
# pahole -C xfs_inode_log_format xfs-arm-eabi.ko
struct xfs_inode_log_format {
__uint16_t ilf_type; /* 0 2 */
__uint16_t ilf_size; /* 2 2 */
__uint32_t ilf_fields; /* 4 4 */
__uint16_t ilf_asize; /* 8 2 */
__uint16_t ilf_dsize; /* 10 2 */
/* XXX 4 bytes hole, try to pack */
__uint64_t ilf_ino; /* 16 8 */
union {
__uint32_t ilfu_rdev; /* 4 */
uuid_t ilfu_uuid; /* 16 */
} ilf_u; /* 24 16 */
__int64_t ilf_blkno; /* 40 8 */
__int32_t ilf_len; /* 48 4 */
__int32_t ilf_boffset; /* 52 4 */
/* size: 56, cachelines: 1, members: 10 */
/* sum members: 52, holes: 1, sum holes: 4 */
/* last cacheline: 56 bytes */
};
That was for an arm eabi xfs.ko from 2.6.25. Don't worry about the "try
to pack" message; as long as holes match everywhere it's ok ;)
...
>> To be honest, I am not certain that this is "worth fixing" - we already
>> have the requirement that log replay can only be done on an architecture
>> of the same endianness, and a further requirement that it can only be
>> done on architectures with similar alignment rules doesn't seem so bad.
>>
>
> Where is the official description of such requirment? The requirment is
> not obvious to new XFS users, and they should be warned :)
For the endian requirement ... not sure where it's doc'd to be honest.
if you don't find it in Documentation/filesystems/xfs.txt feel free to
send a patch ;)
> Why is such requirment? For backward compatibility?
The xfs log was done native-endian for performance reasons, I think.
> I think the requirment is bad. It inhibit user from exchanging data
> freely between systems, which is an obvious requirment for file system
> design.
No, it just means that you have to cleanly unmount on one filesystem
before you try to mount it on another different system.
>> The problem is, if you go off and "fix" this on arm now, you'll find
>> that logs created under older arm kernels can't be replayed on newer arm
>> kernels and vice versa...
>
> Compared with the above restriction("requirment"), we can afford this :)
>
> Do I miss any other log/metadata needs pack on 2.6.10?
I can't really speak to 2.6.10, I don't want to go back that far ;) I'm
afraid you're on your own there.
So just to be clear, on 2.6.28, arm eabi logs replay fine on x86_64?
-Eric
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