On Mon, Apr 27 2009, Boaz Harrosh wrote:
> > +static struct bio *bio_chain_clone(struct bio *old_chain, gfp_t gfpmask)
> > +{
> > + struct bio *tmp, *new_chain = NULL, *tail = NULL;
> > +
> > + while (old_chain) {
> > + tmp = bio_clone(old_chain, gfpmask);
> > + if (!tmp)
> > + goto err_out;
> > +
> > + tmp->bi_next = NULL;
> > + if (!new_chain)
> > + new_chain = tail = tmp;
> > + else {
> > + tail->bi_next = tmp;
> > + tail = tmp;
> > + }
> > +
> > + old_chain = old_chain->bi_next;
> > + }
> > +
> > + return new_chain;
> > +
> > +err_out:
> > + bio_chain_put(new_chain);
> > + return NULL;
> > +}
> > +
>
> NOTE-TO-ME:
> blk_bio_clone()
Note to Boaz - this is illegal, unless gfp_mask is GFP_ATOMIC (in which
case you should not pass it in). The only way to make this work is to:
1) Have a private bio pool, and
2) Make sure it has enough reserved entries to populate the chain, and
3) Ensure only a single caller at the time, or entries enough for the N
users that are allowed. It has to be controlled either way, whether N
is 1 or larger.
> > +static void osdblk_rq_fn(struct request_queue *q)
> > +{
> > + struct osdblk_device *osdev = q->queuedata;
> > + struct request *rq;
> > + struct osdblk_request *orq;
> > + struct osd_request *or;
> > + struct bio *bio;
> > + int do_write, do_flush;
> > +
> > + while (1) {
> > + /* peek at request from block layer */
> > + rq = elv_next_request(q);
> > + if (!rq)
> > + break;
> > +
> > + /* filter out block requests we don't understand */
> > + if (!blk_fs_request(rq) && !blk_barrier_rq(rq)) {
> > + end_request(rq, 0);
> > + continue;
> > + }
> > +
> > + /* deduce our operation (read, write, flush) */
> > + /* I wish the block layer simplified cmd_type/cmd_flags/cmd[]
> > + * into a clearly defined set of RPC commands:
> > + * read, write, flush, scsi command, power mgmt req,
> > + * driver-specific, etc.
> > + */
> > +
> > + do_flush = (rq->special == (void *) 0xdeadbeefUL);
>
> That's for real? or it needs a "FIXME" next to it?
>
> > + do_write = (rq_data_dir(rq) == WRITE);
> > +
> > + /* a bio clone to be passed down to OSD request */
> > + bio = bio_chain_clone(rq->bio, GFP_ATOMIC);
> > + if (!bio)
> > + break;
>
> does blk_barrier_rq() have a rq->bio?
It may or may not.
--
Jens Axboe
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