On 10/24/2012 03:23 PM, Dan Mick wrote:
'segment' is better than 'chunk', but as these are RADOS objects, I really prefer just "object" here to make that clear. Maybe we can add a small block comment explaining the terminology just to make it crystal-clear? rbd_object would be fine with me too. The problem with "segment" is it tends to make me think I'm missing a subdivision of the RADOS objects that make up an rbd image that I didn't know about.
I agree about the naming.
Otherwise, Reviewed-by: Dan Mick <dan.mick@xxxxxxxxxxx> On 10/22/2012 09:51 AM, Alex Elder wrote:The aim of this patch is to make what's going on rbd_merge_bvec() a bit more obvious than it was before. This was an issue when a recent btrfs bug led us to question whether the merge function was working correctly. Use "seg" rather than "chunk" to indicate the units whose boundaries we care about we call "segments." Signed-off-by: Alex Elder <elder@xxxxxxxxxxx> --- drivers/block/rbd.c | 51 +++++++++++++++++++++++++++++++++++---------------- 1 file changed, 35 insertions(+), 16 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 4858d92..4ccce4d 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -1566,22 +1566,41 @@ static int rbd_merge_bvec(struct request_queue *q, struct bvec_merge_data *bmd, struct bio_vec *bvec) { struct rbd_device *rbd_dev = q->queuedata; - unsigned int chunk_sectors; - sector_t sector; - unsigned int bio_sectors; - int max; - - chunk_sectors = 1 << (rbd_dev->header.obj_order - SECTOR_SHIFT); - sector = bmd->bi_sector + get_start_sect(bmd->bi_bdev); - bio_sectors = bmd->bi_size >> SECTOR_SHIFT; - - max = (chunk_sectors - ((sector & (chunk_sectors - 1)) - + bio_sectors)) << SECTOR_SHIFT; - if (max < 0) - max = 0; /* bio_add cannot handle a negative return */ - if (max <= bvec->bv_len && bio_sectors == 0) - return bvec->bv_len; - return max; + sector_t sector_offset; + sector_t sectors_per_seg; + sector_t seg_sector_offset; + int ret; + + /* + * Find how far into its rbd segment the partition-relative + * bio start sector is to offset relative to the enclosing + * device. + */ + sector_offset = get_start_sect(bmd->bi_bdev) + bmd->bi_sector; + sectors_per_seg = 1 << (rbd_dev->header.obj_order - SECTOR_SHIFT); + seg_sector_offset = sector_offset & (sectors_per_seg - 1); + + /* + * Compute the number of bytes from that offset to the end + * of the segment. Account for what's already used by the bio. + */ + ret = (int) (sectors_per_seg - seg_sector_offset) << SECTOR_SHIFT; + if (ret >= bmd->bi_size) + ret -= bmd->bi_size; + else + ret = 0; + + /* + * Don't send back more than was asked for. And if the bio + * was empty, let the whole thing through because: "Note + * that a block device *must* allow a single page to be + * added to an empty bio." + */ + rbd_assert(bvec->bv_len <= PAGE_SIZE); + if (ret > (int) bvec->bv_len || !bmd->bi_size) + ret = (int) bvec->bv_len; + + return ret; } static void rbd_free_disk(struct rbd_device *rbd_dev)
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