Re: [PATCH] UBIFS: endian handling fixes and annotations

Adrian Hunter
2008-11-24T14:11:07Z

Sebastian Andrzej Siewior wrote:
> * Artem Bityutskiy | 2008-11-21 19:19:24 [+0200]:
>
>> index 9ee6508..3f1f16b 100644
>> --- a/fs/ubifs/key.h
>> +++ b/fs/ubifs/key.h
>> @@ -345,7 +345,7 @@ static inline int key_type_flash(const struct ubifs_info *c, const void *k)
>> {
>> const union ubifs_key *key = k;
>>
>> - return le32_to_cpu(key->u32[1]) >> UBIFS_S_KEY_BLOCK_BITS;
>> + return le32_to_cpu(key->j32[1]) >> UBIFS_S_KEY_BLOCK_BITS;
>
> If you would change such references to something like
> |return le32_to_cpup(&key->j32[1]) >> UBIFS_S_KEY_BLOCK_BITS;
> then on powerpc
>
> text data bss dec hex filename
> 155384 1284 24 156692 26414 ubifs-b4.ko
> 155372 1284 24 156680 26408 ubifs-after.ko
>
> because now it is possible to load the value as LE from memory instead
> of loading it BE and swapping it afterwads.

Wouldn't that be true for every le32_to_cpu of an lvalue? Shame you can't
do:

is_lvalue(x) ? le32_to_cpup(&(x)) : le32_to_cpu(x)

>> }
>>
>> /**
>> @@ -416,7 +416,7 @@ static inline unsigned int key_block_flash(const struct ubifs_info *c,
>> {
>> const union ubifs_key *key = k;
>>
>> - return le32_to_cpu(key->u32[1]) & UBIFS_S_KEY_BLOCK_MASK;
>> + return le32_to_cpu(key->j32[1]) & UBIFS_S_KEY_BLOCK_MASK;
>> }
>
> This and the previous change look like a bugfix for something that
> should trigger during recovery or something? Shouldn't I fail in
> ubifs_validate_entry() during recovery?

This is just about casting. key->u32[1] and key->j32[1] are the same object.
There is no "real" bug in these two cases - just compilation warnings.

>> /**
>> diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c
>> index 77d26c1..bed9742 100644
>> --- a/fs/ubifs/recovery.c
>> +++ b/fs/ubifs/recovery.c
>> @@ -168,12 +168,12 @@ static int write_rcvrd_mst_node(struct ubifs_info *c,
>> struct ubifs_mst_node *mst)
>> {
>> int err = 0, lnum = UBIFS_MST_LNUM, sz = c->mst_node_alsz;
>> - uint32_t save_flags;
>> + __le32 save_flags;
>>
>> dbg_rcvry("recovery");
>>
>> save_flags = mst->flags;
>> - mst->flags = cpu_to_le32(le32_to_cpu(mst->flags) | UBIFS_MST_RCVRY);
>> + mst->flags |= cpu_to_le32(UBIFS_MST_RCVRY);
>
> another micro optimisation would be to use __constant_cpu_to_le32()

As per Harvey's reply.