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Some semplification of the delta parity computation.

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There is no functional change in the code, only made explicit
some invariants.
This commit is contained in:
Andrea Mazzoleni 2014-09-17 21:48:23 +02:00
parent 3a798cb226
commit f21d86e999
1 changed files with 24 additions and 13 deletions
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37
raid/raid.c
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@ -205,8 +205,8 @@ void raid_zero(void *zero)
* @nd Number of data blocks
* @size Size of the blocks pointed by @v. It must be a multipler of 64.
* @v Vector of pointers to the blocks of data and parity.
* It has (@nd + #parities) elements. The starting elements are the blocks for
* data, following with the parity blocks.
* It has (@nd + #parities) elements. The starting elements are the blocks
* for data, following with the parity blocks.
* Each block has @size bytes.
*/
void (*raid_gen_ptr[RAID_PARITY_MAX])(int nd, size_t size, void **vv);
@ -275,8 +275,7 @@ void raid_invert(uint8_t *M, uint8_t *V, int n)
* Computes the parity without the missing data blocks
* and store it in the buffers of such data blocks.
*
* This is the parity expressed as Pa,Qa,Ra,Sa,Ta,Ua
* in the equations.
* This is the parity expressed as Pa,Qa,Ra,Sa,Ta,Ua in the equations.
*/
void raid_delta_gen(int nr, int *id, int *ip, int nd, size_t size, void **v)
{
@ -286,7 +285,8 @@ void raid_delta_gen(int nr, int *id, int *ip, int nd, size_t size, void **v)
int np;
void* latest;
/* number of parities used */
/* total number of parities we are going to process */
/* they are both the used and the unused ones */
np = ip[nr - 1] + 1;
/* latest missing data block */
@ -297,7 +297,7 @@ void raid_delta_gen(int nr, int *id, int *ip, int nd, size_t size, void **v)
/* keep a copy of the original parity vector */
p[i] = v[nd + i];
if (j < nr && ip[j] == i) {
if (ip[j] == i) {
/*
* Set used parities to point to the missing
* data blocks.
@ -306,6 +306,10 @@ void raid_delta_gen(int nr, int *id, int *ip, int nd, size_t size, void **v)
* to point to the "zero" buffer.
*/
/* the latest parity to use ends the for loop and */
/* then it cannot happen to process more of them */
BUG_ON(j >= nr);
/* buffer for missing data blocks */
pa[j] = v[id[j]];
@ -324,20 +328,27 @@ void raid_delta_gen(int nr, int *id, int *ip, int nd, size_t size, void **v)
* functions able to compute only a subset of
* parities.
*
* To avoid this, we use reuse parity buffers, assuming
* that all the parity functions write parities in order.
* To avoid this, we use reuse parity buffers,
* assuming that all the parity functions write
* parities in order.
*
* We assign the unused parity block to the same block of the
* latest used parity that we know it will be written.
* We assign the unused parity block to the same
* block of the latest used parity that we know it
* will be written.
*
* This means that this block will be written multiple times
* and only the latest write will contain the correct data.
* This means that this block will be written
* multiple times and only the latest write will
* contain the correct data.
*/
v[nd + i] = latest;
}
}
/* recompute the minimal parity required */
/* all the parities have to be processed */
BUG_ON(j != nr);
/* recompute the parity, note that np may be smaller than the */
/* total number of parities available */
raid_gen(nd, np, size, v);
/* restore data buffers as before */